Astronomy

What is the highest angle the moon ever makes above the horizon at the North Pole?

What is the highest angle the moon ever makes above the horizon at the North Pole?


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The question is in the title. I'd like to find out the maximum angle the moon ever makes above the horizon at the North Pole. By "the horizon at the North Pole," I mean the tangent plane to the earth at that point.

Note that I'm not asking for the highest angle that the moon ever appears to make above the horizon. Appearances are distorted by refraction, etc., although I'm not sure by how many degrees. Though I'd be interested in the exact distortion: is there a data repository where I can look up the highest observed angle?

I would make the following prediction. The moon's orbital plane is inclined to the earth's equatorial plane at about $23.5+5approx 28.5$ degrees. Let $R_e$ denote the radius of the earth and $R$ denote the radius of the moon's orbit around the moon. A little geometry for the highest point suggests

$$ heta_{ ext{max}}= an^{-1}left(frac{Rsin(28.5^{circ})-R_e}{Rcos(28.5^{circ})} ight)$$

But because $R>>R_e$ (about 385,000 compared to 6300 km), $ heta_{ ext{max}}$ should be just a little less than $28.5^{circ}$.

Is this right?


${R_e}/{R}$ is about 0.017 radian or 1°. Using your trigonometry and these values:

  • Lunar orbit inclination = 5.15° (varies between 5.0° and 5.3°)
  • Lunar perigee = 362600 km, apogee = 405400 km
  • Earth polar radius = 6357 km
  • Ecliptic obliquity = 23.44°

I get 27.7° at perigee and 27.8° at apogee. At that altitude, atmospheric refraction is only about 0.03°. The highest apparent altitude I found with JPL HORIZONS was 27.91° on 1987-09-15 around 17:15 UT.

Due to nodal precession, the Moon doesn't reach ±28.6° geocentric declination every year, only near a major lunar standstill every 18 or 19 years, e.g. in 2006 or 2025. Near a minor lunar standstill, e.g. in 2015, the Moon's declination is limited to ±18.3°.


One should consider the problem as relative position between EARTH and MOON only, irrespective of EARTH's tilt w.r.t. ecliptic. I am not able to put up a sketch here but would explain as-- Thus if we consider the geometry between EARTH and MOON, then as per my calculation as : The C to C distance = 383,000 km @ 5.145 deg inclined, Horizontal distance will be = 383000 x COS( 5.145) = 381,452 km. AND the vertical distance above north pole = 383,000 x SIN ( 5.145)- 6317 (radius of EARTH)- 1737 (radius of MOON) = 26,338 km. Thus highest inclination above NORTH POLE tangent plane is Arc TAN ( 26338 / 381452 ) = 3.944 deg.


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5 Facts Everyone Must Know Now That The Solstice Is Over

From the northern hemisphere, the winter solstice marks the lowest, shortest path that the Sun takes . [+] throughout the sky.

Danilo Pivato of http://www.danilopivato.com/

As the year draws to a close, we approach a very special time of year, at least from an astronomical perspective. This past Thursday, December 21st, marked the Winter Solstice in the Northern Hemisphere, or the date where the Earth’s axis is tilted its maximal amount away from the Sun, as viewed from an observer north of the equator. Sure, it’s pretty common knowledge that the Earth’s revolution around the Sun in conjunction with its axial tilt is the reason for the seasons. But the December solstice — one of the two days where the Earth’s tilt is maximally inclined with respect to the Sun — brings a number of special things along with it that are unique to this time of year. Here are the top 5.

No one has ever taken a 360-degree star trail photo from Earth before. This photo was actually a . [+] 12-hour exposure, on a mount scheduled to rotate at a rate of 15-degrees-per-hour to create the almost 360-degree effect.

Earl Moser, via http://www.astro-tom.com/

1.) A dedicated astrophotographer living North of the Arctic Circle could take the first-ever 360-degree star trail photo!

Never-yet-accomplished, Lewin’s Challenge requires 24 hours of consecutive darkness, something that happens for six continuous months, centered on the solstices, at each of the poles. As we cycle through our orbit, the equinoxes mark a time when every location on Earth receives 12 hours of daylight and 12 hours of night. Subsequently, one of the poles plunges into darkness, with progressively lower and lower (numbered) latitudes surrounding that pole joining the party. This reaches its peak on the Solstice, where all latitudes within 23.5 degrees of the pole-in-darkness (so everyone north of 66.5 degrees on Saturday’s Solstice) will receive 24 hours of sunless skies. If you're far enough north, you'll spend that entire time with stars visible, and in darkness, as well.

If you can get inside the Arctic circle, have clear skies, and leave your shutter open, properly centered on the North Pole, you could be the first one! Anyone in (or north of) Cornwallis Island, Canada, Longyearbyen, Norway, or Qaanaaq, Greenland, willing to give it a shot?

During the winter solstice, the farther north you are, the lower the Sun appears at every moment, . [+] including at its highest, above the horizon. From Fairbanks, AK, as shown here, it never gets more than a few degrees above the horizon.

2.) Anyone living north of the 43rd parallel will, on the Winter Solstice, never have the Sun rise higher in the sky than it appears all day at the South Pole!

That’s right, the South Pole — one of our favorite metaphors for a cold, dark, remote place — will have the Sun be higher above the horizon all day than locations like Madison, WI, Portland, OR, all of Germany, Poland, England and nearly all of Russia will see at any time during the day! In fact, for a modest location like Portland, OR, with a latitude of 45.6 degrees N, it will take around a week for the Sun to reach an angle above the horizon that exceeds what you’d see at the South Pole, while for an observer in Anchorage, AK, that won’t happen for another six weeks!

Just 800 years ago, perihelion and the winter solstice aligned. Due to the precession of Earth's . [+] orbit, they are slowly drifting apart, completing a full cycle every 21,000 years.

Greg Benson at Wikimedia Commons

3.) The Winter Solstice now occurs very close to perihelion, or the Earth’s closest position to the Sun, but that is slowly changing over time!

The Earth’s orbit around the Sun makes an almost perfect ellipse, making a complete revolution every year. Well, kind of. You see, there are two types of year: the tropical year, which we define as 365 (or sometimes 366) days, and is the amount of time it takes the Sun to return to the same position it was in the sky approximately one revolution ago, and the sidereal year, which is the amount of time it takes the Earth to return to the same location in space, relative to the background of stars, that it was exactly one revolution ago.

These two measurements of years are slightly different from one another, by one part in about 26,000 combined with the smaller intrinsic precession of Earth’s orbit with respect to the stars (mostly due to the other planets), we get that the Winter Solstice cycles through an entire orbit every 21,000 years. The Winter Solstice coincided with perihelion — which now occurs just a couple of weeks later — just a short 800 years ago, and has been progressively migrating away from it in about 10,000 years, it will be coincident with aphelion, or the point of farthest distance from the Sun! This past Thursday's Winter Solstice was the closest solstice to the Sun you’ll ever experience for the rest of your life!

When the Earth's north pole is maximally tilted away from the Sun, it's maximally tilted towards the . [+] full Moon, on the opposite side of the Earth.

National Astronomical Observatory ROZHEN

4.) The low position of the Sun in the sky means that the full Moon closest to the Solstice, at its highest, will be the highest full Moon above the horizon all year!

Think about it when the Earth’s axis is maximally tilted towards the Sun and the Moon is full — as in, on the other side of the Earth from the Sun — that means the Earth’s axis will be maximally tilted away from the Moon. (To within a maximum error of just 5 degrees, the amount that the Earth-Moon orbital plane is inclined to the Earth-Sun plane.) That means, in a broad sense, that just as the Sun appears to carve its lowest paths through the sky, the full Moons closest to your Winter Solstice carve their highest paths through the sky, and vice versa during the Summer Solstice!

This also means the new Moons closest to the Winter Solstice carve their lowest paths through the sky, and since the new Moon falls close to the Solstice this year, it will be just as low on the horizon as the Sun. Of course, those of you in the Southern Hemisphere will find quite high new Moons and low full Moons as a result at this time of year: exactly the opposite of what those of us in the north will see!

So while Australians are enjoying the Sun riding its highest paths through the sky, here in the north — both two weeks ago and two weeks past the solstice — we’ll enjoy the full Moon, which happens to be a supermoon, doing the same thing!

The observed path that the Sun takes through the sky can be tracked, from solstice to solstice, . [+] using a pinhole camera. That lowest path is the winter solstice, where the Sun reverses course from dropping lower to rising higher with respect to the horizon.

Regina Valkenborgh / www.reginavalkenborgh.com

5.) It's called the "solstice" because the Sun literally "stands still" in the sky.

For approximately a week in each direction around both solstices, the path of the Sun through the sky barely changes at all for all observers in both hemispheres. As such, our word for solstice marks exactly that occurrence, and explains why, if you track the Sun’s path on a daily basis over the course of a year, you’ll see nearly identical tracks near the bottom (marking the Winter Solstice) and the top (marking the Summer Solstice) of all such images.

The Sun's apparent path through the sky on the solstice is vastly different near the equator, at 20 . [+] degrees latitude (left) versus far from the equator, at 70 degrees latitude (right).

Wikimedia Commons user Tauʻolunga

There is a theory that the whole idea of celebrating the new year only began as humans migrated away from the equator, where the difference between the Sun’s path through the sky — and the seasonal climates — became incredibly different. As the Winter Solstice approaches, the Sun’s path dips lower and lower each day. Perhaps you’d fear, if you didn’t know any better, that it might drop below the horizon entirely and disappear forever. But the Solstice marks its minimum point, and then a few days afterwards, it noticeably begins to rise again. Hence, the Sun would return to its dazzling spring-and-summer heights, and a new year would begin. Perhaps that’s where rituals such as New Year’s, Christmas, and other just-post-solstice “rebirth” celebrations owe their origins to!

And there's a special solstice bonus for those of you who care about humanity's ventures to journey into space.

On the winter solstice, 1968, the Apollo 8 crew was launched, bringing the first humans into orbit . [+] around the Moon.

NASA’s Apollo Image Gallery / NASA image S68–56050

6.) It was on the Winter Solstice in 1968 that humans, for the first time, were launched to the Moon!

The Apollo 8 mission, the first manned mission to reach and orbit the Moon, was launched on the Winter Solstice in 1968, exactly 46 years ago this Sunday. The first humans to ever see the Earth from such a great distance, Frank Borman, Jim Lovell and Bill Anders began their journey away from Earth on the Winter Solstice, the darkest evening of the year.

Three days later, they plunged behind the Moon, and both the Sun and the Earth became invisible for a few hours. When those few hours passed, first the Sun and then the Earth re-emerged over the limb of the Moon. This was what they saw.

The first view with human eyes of the Earth rising over the limb of the Moon. This was perhaps the . [+] greatest moment in education / public outreach for NASA until the first moon landing.

As Bill Anders said almost immediately,

“We came all this way to explore the Moon, and the most important thing is that we discovered the Earth.”

So enjoy the solstice however you see fit, and as you do, try and remember this: whether you’re bathed in the longest day or the longest night of the year, there are some things that we all have in common and can bring us all together. The story of where we are and how we came to be here — on Earth, in the Solar System and in the Universe — just might be the most omnipresent of them all.


What is the highest angle the moon ever makes above the horizon at the North Pole? - Astronomy

Exploring the Heavens: all
Chapter 1: 1.1,1.2
Chapter 2: 2.1,2.2,2.3
Chapter 3: all

Using your calculator / Unit Conversions

Reason for the Seasons (Where is the Sun?)

Phases of the Moon and Eclipses

Parallax: angle = baseline/distance

Electromagnetic Spectrum: wavelength x frequency = velocity

Answers are at the end of each section, so scroll down carefully if you don't want to see them right away.

In addition to the questions, you should know the speed of light, and how to calculate the distance of an object if you know your baseline and the parallax angle between your two observing locations.

Using your calculator / Unit Conversions

how many minutes is 3.50° (answer 210')

how many degrees is 7.00' (answer .117°)

how many minutes is 5.30" (answer 0.0883' = 8.83x10 -2 ')

how many degrees is 5.30" (answer 1.47x10 -3 ° this one requires 2 steps)

how many degrees is 1.00 radian (answer 57.3°)

how many radians is 4.00° (answer 6.98x10 -2 rad)

how many radians is 23.5' (answer 6.84x10 -3 rad this one requires 2 steps)

how many radians is 16.3" (answer 7.90x10 -5 rad this one requires 3 steps))

General View of the Sky (6 questions)

1) Durango&rsquos latitude is +37.275° N. What is the southernmost Declination observable from Durango?

2) The angle that the North Star (Polaris) makes with the horizon (its&rsquo height above the horizon) changes noticeably

A) as hours go by during the night

B) as months go by during the year

C) as you change latitude on Earth

D) as you change longitude on Earth

3) About how many stars can you see at one time from Durango with your naked eye?

4) About how many constellations can you see at one time?

5) Which coordinate is measured in degrees north and south of the equator?

E) Both A and B are correct.

6) From the horizon to the observer's zenith is an angle of:

A) 23.5 degrees for observers at the Tropics of Cancer and Capricorn.

B) 30 degrees for observers in north Florida, at a latitude of 30 degrees north.

C) 47 degrees over the course of the entire year.

D) 57 degrees for everyone on the earth.

E) 90 degrees for everyone on the earth.

Science/History of Astronomy (4 questions)

1) Is it possible to prove or disprove a scientific theory?

2) In Ptolemy's geocentric model, the retrograde motion occurs when the planet is closest to us, on the inside portion of the:

3) A fatal flaw with Ptolemy's model is its inability to predict the observed phases of:

B) the Sun during an eclipse.

C) the Moon in its monthly cycle.

4) Which of these was NOT a telescopic discovery of Galileo?

A) the craters and mare of the Moon

C) sunspots and the rotation of the Sun

D) the four largest moons of Jupiter

Reason for the Seasons (Where is the Sun?) (7 questions)

1) Why is it cold at the North Pole, even during northern hemisphere summer?

A) Because the "pole" itself doesn&rsquot point very close to the direction of the Sun

B) Because there are fewer daylight hours at the pole than at lower latitudes (e.g., Durango)

C) Because of the high altitude at the pole

D) Because the pole is further away from the Sun than lower latitudes are (e.g., Durango)

2) Observing from a latitude of 25° North

A) The star Polaris appears about 65° above the horizon.

B) The celestial equator has a maximum height of 65° above the horizon.

C) The star Polaris appears about 25° north of the zenith point.

D) The celestial equator has a maximum height of 25° above the horizon.

3) Northern spring (March 21 to June 21) and autumn (Sept 21 to Dec 21) are the hottest seasons of the year at

C) The tropic of capricorn.

4) A sidereal day on Earth is:

B) About four minutes shorter than a solar day.

C) About four minutes longer than a solar day.

D) The time between full moons.

5) In Paris, France (50 degrees north latitude), what is the longest day of the year?

6) Where along the horizon does the Sun rise on June 21 in Sydney, Australia?

D) Can&rsquot tell with information given

7) You are in Paris, France (50 degrees north latitude), on June 21. What is the highest angle above the horizon that the Sun achieves?

A) 16.5° above the Southern horizon

B) 26.5° above the Southern horizon

C) 63.5° above the Southern horizon

D) 73.5° above the Southern horizon

Phases of the Moon and Eclipses (6 questions)

A) The new moon rises at noon.

B) The first quarter moon rises at noon.

C) The full moon rises at noon.

D) The third quarter moon rises at noon.

2) On December 21, in Durango, if there is a full moon, where does it rise?

B) Almost due east (within 5 degrees)

C) South of east (by more than 5 degrees)

D) North of east (by more than 5 degrees)

3) Assume that the Sun rises at 6:00 A.M. What time does the third quarter Moon rise?

4) If new Moon fell on March 2nd, what is the Moon's phase on March 14th?

5) If the Moon appears half lit, and is almost overhead about 6:00 AM, its phase is:

6) What conditions are needed to produce a total lunar eclipse?

A) full Moon on the equator at perigee

B) new Moon on equator at apogee

C) new Moon on ecliptic at perigee

D) any time the Moon crosses the ecliptic, the path of eclipses

E) full Moon on the ecliptic

Parallax: angle = baseline/distance (4 questions)

1) Star A has a parallax shift of 0.4 arc seconds. Star B has a parallax shift of 0.6 arc seconds

A) B is 1.5 times as far away as A

B) Star A is at a distance of 4 parsecs (pc)

C) Star B is at a distance of 1.66 parsecs (pc)

D) Star A is 0.4 times as far away as B

2) The parallax angle becomes:

A) larger as the distance to the object increases.

B) larger as the separation between the two observing sites increases.

C) smaller as the distance to the object increases

D) Both A and B are correct.

E) Both B and C are correct.

3) Star A has a parallax shift of 0.3 arc seconds. Star B has a parallax shift of 0.9 arc seconds.

A) Star B is three times as far as star A

B) Star A is at a distance of 1.5 pc

C) Star B is at a distance of 9 pc

D) Star B is three times closer than star A

4) You observe a classmate walking in the distance. He appears to subtend a vertical angle of 0.017 radians. You know that he is 1.7 meters tall. How far away is he?

Electromagnetic Spectrum: wavelength x frequency = velocity (4 questions)

A) wavelength / velocity = frequency

B) wavelength / velocity = period

C) wavelength * frequency = period

D) wavelength * velocity = frequency

2) The speed of light in a vacuum is written as:

A) v = 186,000 miles per hour.

3) The period of a wave in a large crowd at a football game is 3.0 seconds. The wavelength of this wave is 45 meters. The speed of the wave is:

4) Which list is in the correct order of electromagnetic radiation wavelength, going from shortest to longest?

A) infrared, ultraviolet, gamma, radio

B) gamma, x-ray, ultraviolet, visible

C) radio, infrared, visible, ultaviolet

D) radio, x-ray, ultraviolet, visible

A) gathers 5 times as much light as a 1 m telescope

B) gathers 1/2 as much light as a 10 m telescope

C) gathers 4 times as much light as a 2.5 m telescope

D) gathers 5/2 as much light as a 2 m telescope

2) The resolving power of a telescope is

A) Its ability to see very faint objects

B) Its ability to distinguish two adjacent object close together in the sky

C) Its ability to make distant objects appear much closer to us

D) Its ability to separate light into its component colors for analysis

E) Its ability to focus more than just visible light for imaging

3) What is the primary purpose of a telescope?

A) to magnify distant objects

B) to separate light into its component wavelengths

C) to measure the brightness of stars very accurately

D) to collect a large amount of light and bring it into focus

E) to make distant objects appear nearby

4) The design of modern x-ray telescopes depends on:

A) lenses made of germanium

B) the prime focus design, with mirrors made of iron

C) grazing incidence optics

D) achromatic lenses to keep the x-rays in focus

E) the Cassegrain design, with mirrors made of lead

5) A telescope has an 8 inch diameter primary mirror. Which of the following is true:

A) It gathers twice as much light as a telescope with a 4 inch diameter mirror

B) It gathers four times as much light as a telescope with a 4 inch diameter mirror

C) It gathers half as much light as a telescope with a 16 inch diameter mirror

D) It gathers 2.54 times as much light as a telescope with an 8 cm diameter mirror

E) It gathers more light than an eight inch refractor.

6) A telescope has an 8 inch diameter primary mirror. Which of the following is true:

A) It resolves details twice as small as a telescope with a 4 inch diameter mirror

B) It resolves details four times as small as a telescope with a 4 inch diameter mirror

C) It resolves details almost as small as a telescope with a 16 inch diameter mirror

D) It can resolve details as small as 0.01 arc seconds

E) It can see the Apollo 11 flag on the Moon.

1) Which statement about planetary orbits is incorrect?

A) All planets orbit the Sun counterclockwise.

B) Most stay close to the earth's equator in the sky.

C) Most orbits are almost circular, with low eccentricities.

D) All have the Sun at one focus of their elliptical orbits.

E) Most also rotate counterclockwise on their axes as well.

2) Two planets have orbits with the same sized semi-major axis. Which is true?

A) The planet with the most eccentric orbit moves faster all the time.

B) The planet with the most eccentric orbit moves faster some of the time.

C) The planet with the most eccentric orbit never moves faster.

D) Not enough information to answer.

3) A planet orbit could be circular.

4) Assume a planet orbits exactly three times as far from the Sun as the Earth.

A) It&rsquos period is 3 years exactly.

B) It&rsquos period is between 3 and 5 years

C) It&rsquos period is between 5 and 7 years

D) It&rsquos period is 7 years or more.

5) Assume a planet orbits exactly twice as far from the Sun as the Earth does.

A) It&rsquos period is 2 years exactly.

B) It&rsquos period is between 2 and 3 years

C) It&rsquos period is between 3 and 4 years

D) It&rsquos period is 4 years exactly.

7) Two planets have orbits with the same periods. Which is true?

A) Their velocities must be the same.

B) They must have the same eccentricity.

C) They must have the same semi-major axis.

D) Their orbits must be identical.

1) A brick hits a glass window. The brick breaks the glass, so the magnitude of the force of the brick on the glass is

A) is greater than the magnitude of the force of the glass on the brick

B) is smaller than the magnitude of the force of the glass on the brick

C) is equal to the magnitude of the force of the glass on the brick

D) none of the preceding

2) An iron weight and a styrofoam ball are dropped from the same height at the same time.

Which hits the ground first?

A) The iron weight

B) The styrofoam ball

C) They hit at the same time

3) Which has the most kinetic energy?

A) A 1 kg Mass with velocity 4 m /s.

B) A 2 kg Mass with velocity 3 m /s.

C) A 3 kg Mass with velocity 2 m /s.

D) A 4 kg Mass with velocity 1 m /s.

4) A net force of 15 N is applied to an object with mass 5 kg. According to Newton&rsquos 2 nd Law&hellip

A) The acceleration is 3 m/s 2

B) The acceleration is 45 m/s 2

C) The acceleration is 15 m/s 2

D) The acceleration is .25 m/s 2

5) Which mass pair has the greatest gravitational force between them?

A) A 5Msolar mass and a 4Msolar mass separated by 4 AU.

B) A 4Msolar mass and a 3Msolar mass separated by 3 AU.

C) A 3Msolar mass and a 2Msolar mass separated by 2 AU.

D) A 2Msolar mass and a 1Msolar mass separated by 1 AU.

6) On top of a very high mountain, you would "weigh"&hellip

A) Less than at sea level

B) The same as at sea level

C) More than at sea level.


What is the highest angle the moon ever makes above the horizon at the North Pole? - Astronomy

I am an artist who is very interested in Astronomy but does not know very much about it. I very much enjoyed reading your extremely helpful website.

I would like to know, as precisely as possible, when the moon will shine at its brightest through the hole in the Pantheon in Rome. The Pantheon has a circular hole of 9m across at the centre of it's dome as shown here.

As your website suggests I have visited the U.S. Naval Observatory Data Services website but the closest I can get is Rome, Italy. What will I need to do to be 100% certain that the date and time given on this website will allow the bright moon to be seen through this narrow opening in the Pantheon roof?

Thanks for your question to . What follows is a rather lengthy and technical answer. I guess I got interested in figuring out the best answer to your problem (presumably that's why I am an Astronomer!), although as a caveat I want to note that it's actually not that easy of a question to answer, so I don't promise to have thought of all the best solutions. Anyway here goes.

Rome has a latitude of 41.9 degrees North (longitude 12.45 W). An object which passes through the zenith at this location therefore must have a declination of 41.9N (right acsension and declination are a co-ordinate system used for objects in the sky which is referenced to the equator and poles of the Earth). This declination is not possible for the Moon, which can only ever have declinations between 28.5S and 28.5N. The highest the Moon will ever get in the sky above Rome is therefore 13.5 deg off zenith, at which point it would illuminate part of the Pantheon, just at an oblique angle (ie. part would be in "Moon shadow").

A Google search gives 43.3m as the height of the interior of the Pantheon dome. A person standing directly below the hole therefore can see an area of the sky around the zenith of radius 5.9 deg (arctan(4.5/43.3)) So the full Moon (diameter 0.5 deg) can be seen in full from the floor of the Pantheon directly below the hole if it has an altitude between 84.3 and 90 degrees (ie. within 5.7 deg of directly overhead). As described above this cannot happen. However, when the Moon reaches 13.5 degrees off Zenith (ie. ALT=76.5) moonlight will fall on a spot about 6m from the centre of the Pantheon. At lower altitudes the moonlight will fall further and further from the centre until it starts falling on the walls and finally cannot be seen directly through the hole in the roof at all.

The highest position of the Full Moon occurs in the winter months when the Sun is at it's lowest in the sky - the Full Moon is exactly opposite the Sun in the sky.

Date of Full Moons in 2006:

Highest point of Moon
Local Time ALT AZ
Jan 14: 0:00 74.9 179.4
Dec 4: 23:50 74.9 176.7
Dec 5: 0:00 74.9 185.0
Jan 2 (2007): 23:40 76.1 179.5
Jan 3: 0:00 75.6 197.0

You'll notice that these high points all happen in the middle of the night - perhaps not ideal for an art exhibition. This is because the Full Moon always rises at sunset, therefore reaches its highest point in the middle of the night. You'll also notice that the altitudes are not equal to the theoretical maximum. That's because none of these dates fall exactly on the winter solstice.

For the Moon to be at it's highest in the evening, it has to be First quarter. In this phase, the Moon reaches its highest points at the Spring Equinox.

First quarter Moons in 2006

Highest point of Moon
Local Time ALT AZ Percent illuminated
Feb 5: 18:20 69.7 178.2 0.55
Mar 6: 18:20 74.9 194.5 0.49
Apr 5: 18:40 75.1 181.9 0.52

Which date/time will give the best illumiation is not something which is very easy to answer. You need to reach a comprimise between the amount of the Moon which is illuminated verses how late at night it reaches it's highest point. Also note that the Full Moon doesn't fall exactly on the winter solstice in 2006, neither does the First quarter Moon fall exactly on the Spring equinox.

In summary:

  1. The Moon never passes directly overhead in Rome, Italy.
  2. The Full Moon reaches its highest point at

I think I would pick a Moon in a phase between Full and First quarter, in early Spring, for example Feb 9th or March 10th when the Moon is about 70% illuminated and reaches its highest point around 9pm local time. If you're OK with an exhibition at midnight you can do it on a Full Moon in the middle of winter.

As a final note, Azimuth refers to the angle around the horizon. 180 degs is due South, so to be in "direct moonlight" on these nights, you need to be on the Northern side of the Pantheon, about 6-8m from the central point.

Good luck with the exhibition.

This page was last updated on July 18, 2015.

About the Author

Karen Masters

Karen was a graduate student at Cornell from 2000-2005. She went on to work as a researcher in galaxy redshift surveys at Harvard University, and is now on the Faculty at the University of Portsmouth back in her home country of the UK. Her research lately has focused on using the morphology of galaxies to give clues to their formation and evolution. She is the Project Scientist for the Galaxy Zoo project.


Contents

The Earth's axis of rotation – and hence the position of the North Pole – was commonly believed to be fixed (relative to the surface of the Earth) until, in the 18th century, the mathematician Leonhard Euler predicted that the axis might "wobble" slightly. Around the beginning of the 20th century astronomers noticed a small apparent "variation of latitude", as determined for a fixed point on Earth from the observation of stars. Part of this variation could be attributed to a wandering of the Pole across the Earth's surface, by a range of a few metres. The wandering has several periodic components and an irregular component. The component with a period of about 435 days is identified with the eight-month wandering predicted by Euler and is now called the Chandler wobble after its discoverer. The exact point of intersection of the Earth's axis and the Earth's surface, at any given moment, is called the "instantaneous pole", but because of the "wobble" this cannot be used as a definition of a fixed North Pole (or South Pole) when metre-scale precision is required.

It is desirable to tie the system of Earth coordinates (latitude, longitude, and elevations or orography) to fixed landforms. However, given plate tectonics and isostasy, there is no system in which all geographic features are fixed. Yet the International Earth Rotation and Reference Systems Service and the International Astronomical Union have defined a framework called the International Terrestrial Reference System.

Pre-1900

As early as the 16th century, many prominent people correctly believed that the North Pole was in a sea, which in the 19th century was called the Polynya or Open Polar Sea. [6] It was therefore hoped that passage could be found through ice floes at favorable times of the year. Several expeditions set out to find the way, generally with whaling ships, already commonly used in the cold northern latitudes.

One of the earliest expeditions to set out with the explicit intention of reaching the North Pole was that of British naval officer William Edward Parry, who in 1827 reached latitude 82°45′ North. In 1871, the Polaris expedition, a US attempt on the Pole led by Charles Francis Hall, ended in disaster. Another British Royal Navy attempt to get to the pole, part of the British Arctic Expedition, by Commander Albert H. Markham reached a then-record 83°20'26" North in May 1876 before turning back. An 1879–1881 expedition commanded by US naval officer George W. De Long ended tragically when their ship, the USS Jeannette, was crushed by ice. Over half the crew, including De Long, were lost.

In April 1895, the Norwegian explorers Fridtjof Nansen and Hjalmar Johansen struck out for the Pole on skis after leaving Nansen's icebound ship Fram. The pair reached latitude 86°14′ North before they abandoned the attempt and turned southwards, eventually reaching Franz Josef Land.

In 1897, Swedish engineer Salomon August Andrée and two companions tried to reach the North Pole in the hydrogen balloon Örnen ("Eagle"), but came down 300 km (190 mi) north of Kvitøya, the northeasternmost part of the Svalbard archipelago. They trekked to Kvitøya but died there three months after their crash. In 1930 the remains of this expedition were found by the Norwegian Bratvaag Expedition.

The Italian explorer Luigi Amedeo, Duke of the Abruzzi and Captain Umberto Cagni of the Italian Royal Navy (Regia Marina) sailed the converted whaler Stella Polare ("Pole Star") from Norway in 1899. On 11 March 1900, Cagni led a party over the ice and reached latitude 86° 34’ on 25 April, setting a new record by beating Nansen's result of 1895 by 35 to 40 km (22 to 25 mi). Cagni barely managed to return to the camp, remaining there until 23 June. On 16 August, the Stella Polare left Rudolf Island heading south and the expedition returned to Norway.

1900–1940

The US explorer Frederick Cook claimed to have reached the North Pole on 21 April 1908 with two Inuit men, Ahwelah and Etukishook, but he was unable to produce convincing proof and his claim is not widely accepted. [8] [9]

The conquest of the North Pole was for many years credited to US Navy engineer Robert Peary, who claimed to have reached the Pole on 6 April 1909, accompanied by Matthew Henson and four Inuit men, Ootah, Seeglo, Egingwah, and Ooqueah. However, Peary's claim remains highly disputed and controversial. Those who accompanied Peary on the final stage of the journey were not trained in [Western] navigation, and thus could not independently confirm his navigational work, which some claim to have been particularly sloppy as he approached the Pole.

The distances and speeds that Peary claimed to have achieved once the last support party turned back seem incredible to many people, almost three times that which he had accomplished up to that point. Peary's account of a journey to the Pole and back while traveling along the direct line – the only strategy that is consistent with the time constraints that he was facing – is contradicted by Henson's account of tortuous detours to avoid pressure ridges and open leads.

The British explorer Wally Herbert, initially a supporter of Peary, researched Peary's records in 1989 and found that there were significant discrepancies in the explorer's navigational records. He concluded that Peary had not reached the Pole. [10] Support for Peary came again in 2005, however, when British explorer Tom Avery and four companions recreated the outward portion of Peary's journey with replica wooden sleds and Canadian Eskimo Dog teams, reaching the North Pole in 36 days, 22 hours – nearly five hours faster than Peary. However, Avery's fastest 5-day march was 90 nautical miles, significantly short of the 135 claimed by Peary. Avery writes on his web site that "The admiration and respect which I hold for Robert Peary, Matthew Henson and the four Inuit men who ventured North in 1909, has grown enormously since we set out from Cape Columbia. Having now seen for myself how he travelled across the pack ice, I am more convinced than ever that Peary did indeed discover the North Pole." [11]

The first claimed flight over the Pole was made on 9 May 1926 by US naval officer Richard E. Byrd and pilot Floyd Bennett in a Fokker tri-motor aircraft. Although verified at the time by a committee of the National Geographic Society, this claim has since been undermined [12] by the 1996 revelation that Byrd's long-hidden diary's solar sextant data (which the NGS never checked) consistently contradict his June 1926 report's parallel data by over 100 mi (160 km). [13] The secret report's alleged en-route solar sextant data were inadvertently so impossibly overprecise that he excised all these alleged raw solar observations out of the version of the report finally sent to geographical societies five months later (while the original version was hidden for 70 years), a realization first published in 2000 by the University of Cambridge after scrupulous refereeing. [14]

The first consistent, verified, and scientifically convincing attainment of the Pole was on 12 May 1926, by Norwegian explorer Roald Amundsen and his US sponsor Lincoln Ellsworth from the airship Norge. [15] Norge, though Norwegian-owned, was designed and piloted by the Italian Umberto Nobile. The flight started from Svalbard in Norway, and crossed the Arctic Ocean to Alaska. Nobile, with several scientists and crew from the Norge, overflew the Pole a second time on 24 May 1928, in the airship Italia. The Italia crashed on its return from the Pole, with the loss of half the crew.

The first transpolar flight [ru] was accomplished in a Tupolev ANT-25 airplane with a crew of Valery Chkalov, Georgy Baydukov and Alexander Belyakov, who flew over the North Pole on 19 June 1937.

Ice station

In May 1937 the world's first North Pole ice station, North Pole-1, was established by Soviet scientists by air 20 kilometres (13 mi) from the North Pole. The expedition members—oceanographer Pyotr Shirshov, meteorologist Yevgeny Fyodorov, radio operator Ernst Krenkel, and the leader Ivan Papanin [16] —conducted scientific research at the station for the next nine months. By 19 February 1938, when the group was picked up by the ice breakers Taimyr and Murman, their station had drifted 2850 km to the eastern coast of Greenland. [17] [18]

1940–2000

In May 1945 an RAF Lancaster of the Aries expedition became the first Commonwealth aircraft to overfly the North Geographic and North Magnetic Poles. The plane was piloted by David Cecil McKinley of the Royal Air Force. It carried an 11-man crew, with Kenneth C. Maclure of the Royal Canadian Air Force in charge of all scientific observations. In 2006, Maclure was honoured with a spot in Canada's Aviation Hall of Fame. [19]

Discounting Peary's disputed claim, the first men to set foot at the North Pole were a Soviet party [20] including geophysicists Mikhail Ostrekin and Pavel Senko, oceanographers Mikhail Somov and Pavel Gordienko, [21] and other scientists and flight crew (24 people in total) [22] of Aleksandr Kuznetsov's Sever-2 expedition (March–May 1948). [23] It was organized by the Chief Directorate of the Northern Sea Route. [24] The party flew on three planes (pilots Ivan Cherevichnyy, Vitaly Maslennikov and Ilya Kotov) from Kotelny Island to the North Pole and landed there at 4:44pm (Moscow Time, UTC+04:00) on 23 April 1948. [25] They established a temporary camp and for the next two days conducted scientific observations. On 26 April the expedition flew back to the continent.

Next year, on 9 May 1949 [26] two other Soviet scientists (Vitali Volovich and Andrei Medvedev) [27] became the first people to parachute onto the North Pole. [28] They jumped from a Douglas C-47 Skytrain, registered CCCP H-369. [29]

On 3 May 1952, U.S. Air Force Lieutenant Colonel Joseph O. Fletcher and Lieutenant William Pershing Benedict, along with scientist Albert P. Crary, landed a modified Douglas C-47 Skytrain at the North Pole. Some Western sources considered this to be the first landing at the Pole [30] until the Soviet landings became widely known.

The United States Navy submarine USS Nautilus (SSN-571) crossed the North Pole on 3 August 1958. On 17 March 1959 USS Skate (SSN-578) surfaced at the Pole, breaking through the ice above it, becoming the first naval vessel to do so. [31]

Setting aside Peary's claim, the first confirmed surface conquest of the North Pole was that of Ralph Plaisted, Walt Pederson, Gerry Pitzl and Jean Luc Bombardier, who traveled over the ice by snowmobile and arrived on 19 April 1968. The United States Air Force independently confirmed their position.

On 6 April 1969 Wally Herbert and companions Allan Gill, Roy Koerner and Kenneth Hedges of the British Trans-Arctic Expedition became the first men to reach the North Pole on foot (albeit with the aid of dog teams and airdrops). They continued on to complete the first surface crossing of the Arctic Ocean – and by its longest axis, Barrow, Alaska, to Svalbard – a feat that has never been repeated. [32] [33] Because of suggestions (later proven false) of Plaisted's use of air transport, some sources classify Herbert's expedition as the first confirmed to reach the North Pole over the ice surface by any means. [33] [34] In the 1980s Plaisted's pilots Weldy Phipps and Ken Lee signed affidavits asserting that no such airlift was provided. [35] It is also said that Herbert was the first person to reach the pole of inaccessibility. [36]

On 17 August 1977 the Soviet nuclear-powered icebreaker Arktika completed the first surface vessel journey to the North Pole.

In 1982 Ranulph Fiennes and Charles R. Burton became the first people to cross the Arctic Ocean in a single season. They departed from Cape Crozier, Ellesmere Island, on 17 February 1982 and arrived at the geographic North Pole on 10 April 1982. They travelled on foot and snowmobile. From the Pole, they travelled towards Svalbard but, due to the unstable nature of the ice, ended their crossing at the ice edge after drifting south on an ice floe for 99 days. They were eventually able to walk to their expedition ship MV Benjamin Bowring and boarded it on 4 August 1982 at position 80:31N 00:59W. As a result of this journey, which formed a section of the three-year Transglobe Expedition 1979–1982, Fiennes and Burton became the first people to complete a circumnavigation of the world via both North and South Poles, by surface travel alone. This achievement remains unchallenged to this day.

In 1985 Sir Edmund Hillary (the first man to stand on the summit of Mount Everest) and Neil Armstrong (the first man to stand on the moon) landed at the North Pole in a small twin-engined ski plane. [37] Hillary thus became the first man to stand at both poles and on the summit of Everest.

In 1986 Will Steger, with seven teammates, became the first to be confirmed as reaching the Pole by dogsled and without resupply.

USS Gurnard (SSN-662) operated in the Arctic Ocean under the polar ice cap from September to November 1984 in company with one of her sister ships, the attack submarine USS Pintado (SSN-672). On 12 November 1984 Gurnard and Pintado became the third pair of submarines to surface together at the North Pole. In March 1990, Gurnard deployed to the Arctic region during exercise Ice Ex '90 and completed only the fourth winter submerged transit of the Bering and Seas. Gurnard surfaced at the North Pole on 18 April, in the company of the USS Seahorse (SSN-669). [ citation needed ]

On 6 May 1986 USS Archerfish (SSN 678), USS Ray (SSN 653) and USS Hawkbill (SSN-666) surfaced at the North Pole, the first tri-submarine surfacing at the North Pole.

On 21 April 1987 Shinji Kazama of Japan became the first person to reach the North Pole on a motorcycle. [38] [39]

On 18 May 1987 USS Billfish (SSN 676), USS Sea Devil (SSN 664) and HMS Superb (S 109) surfaced at the North Pole, the first international surfacing at the North Pole.

In 1988 a team of 13 (9 Soviets, 4 Canadians) skied across the arctic from Siberia to northern Canada. One of the Canadians, Richard Weber, became the first person to reach the Pole from both sides of the Arctic Ocean.

On 4 May 1990 Børge Ousland and Erling Kagge became the first explorers ever to reach the North Pole unsupported, after a 58-day ski trek from Ellesmere Island in Canada, a distance of 800 km. [40]

On 7 September 1991 the German research vessel Polarstern and the Swedish icebreaker Oden reached the North Pole as the first conventional powered vessels. [41] Both scientific parties and crew took oceanographic and geological samples and had a common tug of war and a football game on an ice floe. Polarstern again reached the pole exactly 10 years later [42] with the Healy.

In 1998, 1999, and 2000 Lada Niva Marshs (special very large wheeled versions made by BRONTO, Lada/Vaz's experimental product division) were driven to the North Pole. [43] [44] The 1998 expedition was dropped by parachute and completed the track to the North Pole. The 2000 expedition departed from a Russian research base around 114 km from the Pole and claimed an average speed of 20–15 km/h in an average temperature of −30 °C.

21st century

Commercial airliner flights on the Polar routes may pass within viewing distance of the North Pole. For example, the flight from Chicago to Beijing may come close as latitude 89° N, though because of prevailing winds return journeys go over the Bering Strait. In recent years journeys to the North Pole by air (landing by helicopter or on a runway prepared on the ice) or by icebreaker have become relatively routine, and are even available to small groups of tourists through adventure holiday companies. Parachute jumps have frequently been made onto the North Pole in recent years. The temporary seasonal Russian camp of Barneo has been established by air a short distance from the Pole annually since 2002, and caters for scientific researchers as well as tourist parties. Trips from the camp to the Pole itself may be arranged overland or by helicopter.

The first attempt at underwater exploration of the North Pole was made on 22 April 1998 by Russian firefighter and diver Andrei Rozhkov with the support of the Diving Club of Moscow State University, but ended in fatality. The next attempted dive at the North Pole was organized the next year by the same diving club, and ended in success on 24 April 1999. The divers were Michael Wolff (Austria), Brett Cormick (UK), and Bob Wass (USA). [45]

In 2005 the United States Navy submarine USS Charlotte (SSN-766) surfaced through 155 cm (61 in) of ice at the North Pole and spent 18 hours there. [46]

In July 2007 British endurance swimmer Lewis Gordon Pugh completed a 1 km (0.62 mi) swim at the North Pole. His feat, undertaken to highlight the effects of global warming, took place in clear water that had opened up between the ice floes. [47] His later attempt to paddle a kayak to the North Pole in late 2008, following the erroneous prediction of clear water to the Pole, was stymied when his expedition found itself stuck in thick ice after only three days. The expedition was then abandoned.

By September 2007 the North Pole had been visited 66 times by different surface ships: 54 times by Soviet and Russian icebreakers, 4 times by Swedish Oden, 3 times by German Polarstern, 3 times by USCGC Healy and USCGC Polar Sea, and once by CCGS Louis S. St-Laurent and by Swedish Vidar Viking. [48]

2007 descent to the North Pole seabed

On 2 August 2007 a Russian scientific expedition Arktika 2007 made the first ever manned descent to the ocean floor at the North Pole, to a depth of 4.3 km (2.7 mi), as part of the research programme in support of Russia's 2001 extended continental shelf claim to a large swathe of the Arctic Ocean floor. The descent took place in two MIR submersibles and was led by Soviet and Russian polar explorer Artur Chilingarov. In a symbolic act of visitation, the Russian flag was placed on the ocean floor exactly at the Pole. [49] [50] [51]

The expedition was the latest in a series of efforts intended to give Russia a dominant influence in the Arctic according to The New York Times. [52] The warming Arctic climate and summer shrinkage of the iced area has attracted the attention of many countries, such as China and the United States, toward the top of the world, where resources and shipping routes may soon be exploitable. [53]

MLAE 2009 Expedition

In 2009 the Russian Marine Live-Ice Automobile Expedition (MLAE-2009) with Vasily Elagin as a leader and a team of Afanasy Makovnev, Vladimir Obikhod, Alexey Shkrabkin, Sergey Larin, Alexey Ushakov and Nikolay Nikulshin reached the North Pole on two custom-built 6 x 6 low-pressure-tire ATVs. The vehicles, Yemelya-1 and Yemelya-2, were designed by Vasily Elagin, a Russian mountain climber, explorer and engineer. They reached the North Pole on 26 April 2009, 17:30 (Moscow time). The expedition was partly supported by Russian State Aviation. The Russian Book of Records recognized it as the first successful vehicle trip from land to the Geographical North Pole.

MLAE 2013 Expedition

On 1 March 2013 the Russian Marine Live-Ice Automobile Expedition (MLAE 2013) with Vasily Elagin as a leader, and a team of Afanasy Makovnev, Vladimir Obikhod, Alexey Shkrabkin, Andrey Vankov, Sergey Isayev and Nikolay Kozlov on two custom-built 6 x 6 low-pressure-tire ATVs—Yemelya-3 and Yemelya-4—started from Golomyanny Island (the Severnaya Zemlya Archipelago) to the North Pole across drifting ice of the Arctic Ocean. The vehicles reached the Pole on 6 April and then continued to the Canadian coast. The coast was reached on 30 April 2013 (83°08N, 075°59W Ward Hunt Island), and on 5 May 2013 the expedition finished in Resolute Bay, NU. The way between the Russian borderland (Machtovyi Island of the Severnaya Zemlya Archipelago, 80°15N, 097°27E) and the Canadian coast (Ward Hunt Island, 83°08N, 075°59W) took 55 days it was

2300 km across drifting ice and about 4000 km in total. The expedition was totally self-dependent and used no external supplies. The expedition was supported by the Russian Geographical Society. [54]

The sun at the North Pole is continuously above the horizon during the summer and continuously below the horizon during the winter. Sunrise is just before the March equinox (around 20 March) the sun then takes three months to reach its highest point of near 23½° elevation at the summer solstice (around 21 June), after which time it begins to sink, reaching sunset just after the September equinox (around 23 September). When the sun is visible in the polar sky, it appears to move in a horizontal circle above the horizon. This circle gradually rises from near the horizon just after the vernal equinox to its maximum elevation (in degrees) above the horizon at summer solstice and then sinks back toward the horizon before sinking below it at the autumnal equinox. Hence the North and South Poles experience the slowest rates of sunrise and sunset on Earth.

The twilight period that occurs before sunrise and after sunset has three different definitions:

  • a civil twilight period of about two weeks
  • a nautical twilight period of about five weeks and
  • an astronomical twilight period of about seven weeks.

These effects are caused by a combination of the Earth's axial tilt and its revolution around the sun. The direction of the Earth's axial tilt, as well as its angle relative to the plane of the Earth's orbit around the sun, remains very nearly constant over the course of a year (both change very slowly over long time periods). At northern midsummer the North Pole is facing towards the sun to its maximum extent. As the year progresses and the Earth moves around the sun, the North Pole gradually turns away from the sun until at midwinter it is facing away from the Sun to its maximum extent. A similar sequence is observed at the South Pole, with a six-month time difference.

In most places on Earth, local time is determined by longitude, such that the time of day is more or less synchronised to the position of the sun in the sky (for example, at midday, the sun is roughly at its highest). This line of reasoning fails at the North Pole, where the sun rises and sets only once per year, and all lines of longitude, and hence all time zones, converge. There is no permanent human presence at the North Pole and no particular time zone has been assigned. Polar expeditions may use any time zone that is convenient, such as Greenwich Mean Time, or the time zone of the country from which they departed. [ citation needed ]

The North Pole is substantially warmer than the South Pole because it lies at sea level in the middle of an ocean (which acts as a reservoir of heat), rather than at altitude on a continental land mass. Despite being an ice cap, the northernmost weather station in Greenland has a tundra climate (Köppen ET) due to the July and August mean temperatures peaking just above freezing.

Winter temperatures at the northernmost weather station in Greenland can range from about −50 to −13 °C (−58 to 9 °F), averaging around −31 °C (−24 °F), with the North Pole being slightly colder. A However, a freak storm caused the temperature to reach 0.7 °C (33 °F) for a time at a World Meteorological Organization buoy, located at 87.45°N, on 30 December 2015. It was estimated that the temperature at the North Pole was between 30 and 35 °F (−1 and 2 °C) during the storm. [55] Summer temperatures (June, July, and August) average around the freezing point (0 °C (32 °F)). The highest temperature yet recorded is 13 °C (55 °F), [56] much warmer than the South Pole's record high of only −12.3 °C (9.9 °F). [57] A similar spike in temperatures occurred on 15 November 2016 when temperatures hit freezing. [58] Yet again, February 2018 featured a storm so powerful that temperatures at Cape Morris Jesup, the world's northernmost weather station in Greenland, reached 6.1 °C (43 °F) and spent 24 straight hours above freezing. [59] Meanwhile, the pole itself was estimated to reach a high temperature of 1.6 °C (35 °F). This same temperature of 1.6 °C (35 °F) was also recorded at the Hollywood Burbank Airport in Los Angeles at the very same time. [60]

The sea ice at the North Pole is typically around 2 to 3 m (6 ft 7 in to 9 ft 10 in) thick, [61] although ice thickness, its spatial extent, and the fraction of open water within the ice pack can vary rapidly and profoundly in response to weather and climate. [62] Studies have shown that the average ice thickness has decreased in recent years. [63] It is likely that global warming has contributed to this, but it is not possible to attribute the recent abrupt decrease in thickness entirely to the observed warming in the Arctic. [64] Reports have also predicted that within a few decades the Arctic Ocean will be entirely free of ice in the summer. [65] This may have significant commercial implications see "Territorial claims", below.

The retreat of the Arctic sea ice will accelerate global warming, as less ice cover reflects less solar radiation, and may have serious climate implications by contributing to Arctic cyclone generation. [66]

Climate data for Greenlandic Weather Station A (eleven year average observations)
Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Year
Record high °C (°F) −13
(9)
−14
(7)
−11
(12)
−6
(21)
3
(37)
10
(50)
13
(55)
12
(54)
7
(45)
9
(48)
0.6
(33.1)
0.7
(33.3)
13
(55)
Average high °C (°F) −29
(−20)
−31
(−24)
−30
(−22)
−22
(−8)
−9
(16)
0
(32)
2
(36)
1
(34)
0
(32)
−8
(18)
−25
(−13)
−26
(−15)
−15
(6)
Daily mean °C (°F) −31
(−24)
−32
(−26)
−31
(−24)
−23
(−9)
−11
(12)
−1
(30)
1
(34)
0
(32)
−1
(30)
−10
(14)
−27
(−17)
−28
(−18)
−16
(3)
Average low °C (°F) −33
(−27)
−35
(−31)
−34
(−29)
−26
(−15)
−12
(10)
−2
(28)
0
(32)
−1
(30)
−2
(28)
−11
(12)
−30
(−22)
−31
(−24)
−18
(−1)
Record low °C (°F) −47
(−53)
−50
(−58)
−50
(−58)
−41
(−42)
−24
(−11)
−12
(10)
−2
(28)
−12
(10)
−31
(−24)
−21
(−6)
−41
(−42)
−47
(−53)
−50
(−58)
Average relative humidity (%) 83.5 83.0 83.0 85.0 87.5 90.0 90.0 89.5 88.0 84.5 83.0 83.0 85.8
Source: Weatherbase [56]

Polar bears are believed to travel rarely beyond about 82° North. owing to the scarcity of food, though tracks have been seen in the vicinity of the North Pole, and a 2006 expedition reported sighting a polar bear just 1 mi (1.6 km) from the Pole. [67] [68] The ringed seal has also been seen at the Pole, and Arctic foxes have been observed less than 60 km (37 mi) away at 89°40′ N. [69] [70]

Birds seen at or very near the Pole include the snow bunting, northern fulmar and black-legged kittiwake, though some bird sightings may be distorted by the tendency of birds to follow ships and expeditions. [71]

Fish have been seen in the waters at the North Pole, but these are probably few in number. [71] A member of the Russian team that descended to the North Pole seabed in August 2007 reported seeing no sea creatures living there. [50] However, it was later reported that a sea anemone had been scooped up from the seabed mud by the Russian team and that video footage from the dive showed unidentified shrimps and amphipods. [72]

Currently, under international law, no country owns the North Pole or the region of the Arctic Ocean surrounding it. The five surrounding Arctic countries, Russia, Canada, Norway, Denmark (via Greenland), and the United States, are limited to a 200-nautical-mile (370 km 230 mi) exclusive economic zone off their coasts, and the area beyond that is administered by the International Seabed Authority.

Upon ratification of the United Nations Convention on the Law of the Sea, a country has 10 years to make claims to an extended continental shelf beyond its 200-mile exclusive economic zone. If validated, such a claim gives the claimant state rights to what may be on or beneath the sea bottom within the claimed zone. [73] Norway (ratified the convention in 1996 [74] ), Russia (ratified in 1997 [74] ), Canada (ratified in 2003 [74] ) and Denmark (ratified in 2004 [74] ) have all launched projects to base claims that certain areas of Arctic continental shelves should be subject to their sole sovereign exploitation. [75] [76]

In 1907 Canada invoked a "sector principle" to claim sovereignty over a sector stretching from its coasts to the North Pole. This claim has not been relinquished, but was not consistently pressed until 2013. [77] [78]

In some children's Christmas legends and Western folklore, the geographic North Pole is described as the location of Santa Claus' legendary workshop and residence, [79] [80] although the depictions have been inconsistent between the geographic and magnetic North Pole. [ citation needed ] Canada Post has assigned postal code H0H 0H0 to the North Pole (referring to Santa's traditional exclamation of "Ho ho ho!"). [81]

This association reflects an age-old esoteric mythology of Hyperborea that posits the North Pole, the otherworldly world-axis, as the abode of God and superhuman beings. [82]

As Henry Corbin has documented, the North Pole plays a key part in the cultural worldview of Sufism and Iranian mysticism. "The Orient sought by the mystic, the Orient that cannot be located on our maps, is in the direction of the north, beyond the north." [83]

Owing to its remoteness, the Pole is sometimes identified with a mysterious mountain of ancient Iranian tradition called Mount Qaf (Jabal Qaf), the "farthest point of the earth". [84] [85] According to certain authors, the Jabal Qaf of Muslim cosmology is a version of Rupes Nigra, a mountain whose ascent, like Dante's climbing of the Mountain of Purgatory, represents the pilgrim's progress through spiritual states. [86] In Iranian theosophy, the heavenly Pole, the focal point of the spiritual ascent, acts as a magnet to draw beings to its "palaces ablaze with immaterial matter." [87]


Contents

The properties of the orbit described in this section are approximations. The Moon's orbit around Earth has many variations (perturbations) due to the gravitational attraction of the Sun and planets, the study of which (lunar theory) has a long history. [10]

Elliptic shape Edit

The orbit of the Moon is a nearly circular ellipse about the Earth (the semimajor and semiminor axes are 384,400 km and 383,800 km, respectively: a difference of only 0.16%). The equation of the ellipse yields an eccentricity of 0.0549 and perigee and apogee distances of 362,600 km and 405,400 km respectively (a difference of 12%).

Since nearer objects appear larger, the Moon's apparent size changes as it moves toward and away from an observer on Earth. An event referred to as a 'supermoon' occurs when the full Moon is at its closest to Earth (perigee). The largest possible apparent diameter of the Moon is the same 12% larger (as perigee versus apogee distances) than the smallest the apparent area is 25% more and so is the amount of light it reflects toward Earth.

The variance in the Moon's orbital distance corresponds with changes in its tangential and angular speeds, as stated in Kepler's second law. The mean angular movement relative to an imaginary observer at the Earth–Moon barycentre is 13.176 ° per day to the east (J2000.0 epoch).

Elongation Edit

The Moon's elongation is its angular distance east of the Sun at any time. At new moon, it is zero and the Moon is said to be in conjunction. At full moon, the elongation is 180° and it is said to be in opposition. In both cases, the Moon is in syzygy, that is, the Sun, Moon and Earth are nearly aligned. When elongation is either 90° or 270°, the Moon is said to be in quadrature.

Precession Edit

The orientation of the orbit is not fixed in space but rotates over time. This orbital precession is called apsidal precession and is the rotation of the Moon's orbit within the orbital plane, i.e. the axes of the ellipse change direction. The lunar orbit's major axis – the longest diameter of the orbit, joining its nearest and farthest points, the perigee and apogee, respectively – makes one complete revolution every 8.85 Earth years, or 3,232.6054 days, as it rotates slowly in the same direction as the Moon itself (direct motion) - meaning precesses eastward by 360°. The Moon's apsidal precession is distinct from the nodal precession of its orbital plane and axial precession of the moon itself.

Inclination Edit

The mean inclination of the lunar orbit to the ecliptic plane is 5.145°. Theoretical considerations show that the present inclination relative to the ecliptic plane arose by tidal evolution from an earlier near-Earth orbit with a fairly constant inclination relative to Earth's equator. [11] It would require an inclination of this earlier orbit of about 10° to the equator to produce a present inclination of 5° to the ecliptic. It is thought that originally the inclination to the equator was near zero, but it could have been increased to 10° through the influence of planetesimals passing near the Moon while falling to the Earth. [12] If this had not happened, the Moon would now lie much closer to the ecliptic and eclipses would be much more frequent. [13]

The rotational axis of the Moon is not perpendicular to its orbital plane, so the lunar equator is not in the plane of its orbit, but is inclined to it by a constant value of 6.688° (this is the obliquity). As was discovered by Jacques Cassini in 1722, the rotational axis of the Moon precesses with the same rate as its orbital plane, but is 180° out of phase (see Cassini's Laws). Therefore, the angle between the ecliptic and the lunar equator is always 1.543°, even though the rotational axis of the Moon is not fixed with respect to the stars. [14]

Nodes Edit

The nodes are points at which the Moon's orbit crosses the ecliptic. The Moon crosses the same node every 27.2122 days, an interval called the draconic month or draconitic month. The line of nodes, the intersection between the two respective planes, has a retrograde motion: for an observer on Earth, it rotates westward along the ecliptic with a period of 18.6 years or 19.3549° per year. When viewed from the celestial north, the nodes move clockwise around Earth, opposite to Earth's own spin and its revolution around the Sun. An Eclipse of the Moon or Sun can occur when the nodes align with the Sun, roughly every 173.3 days. Lunar orbit inclination also determines eclipses shadows cross when nodes coincide with full and new moon when the Sun, Earth, and Moon align in three dimensions.

In effect, this means that the "tropical year" on the Moon is only 347 days long. This is called the draconic year or eclipse year. The "seasons" on the Moon fit into this period. For about half of this draconic year, the Sun is north of the lunar equator (but at most 1.543°), and for the other half, it is south of the lunar equator. Obviously, the effect of these seasons is minor compared to the difference between lunar night and lunar day. At the lunar poles, instead of usual lunar days and nights of about 15 Earth days, the Sun will be "up" for 173 days as it will be "down" polar sunrise and sunset takes 18 days each year. "Up" here means that the centre of the Sun is above the horizon. [15] Lunar polar sunrises and sunsets occur around the time of eclipses (solar or lunar). For example, at the Solar eclipse of March 9, 2016, the Moon was near its descending node, and the Sun was near the point in the sky where the equator of the Moon crosses the ecliptic. When the Sun reaches that point, the centre of the Sun sets at the lunar north pole and rises at the lunar south pole.

Inclination to the equator and lunar standstill Edit

Every 18.6 years, the angle between the Moon's orbit and Earth's equator reaches a maximum of 28°36′, the sum of Earth's equatorial tilt (23°27′) and the Moon's orbital inclination (5°09′) to the ecliptic. This is called major lunar standstill. Around this time, the Moon's declination will vary from −28°36′ to +28°36′. Conversely, 9.3 years later, the angle between the Moon's orbit and Earth's equator reaches its minimum of 18°20′. This is called a minor lunar standstill. The last lunar standstill was a minor standstill in October 2015. At that time the descending node was lined up with the equinox (the point in the sky having right ascension zero and declination zero). The nodes are moving west by about 19° per year. The Sun crosses a given node about 20 days earlier each year.

When the inclination of the Moon's orbit to the Earth's equator is at its minimum of 18°20′, the centre of the Moon's disk will be above the horizon every day from latitudes less than 70°43' (90° − 18°20' – 57' parallax) north or south. When the inclination is at its maximum of 28°36', the centre of the Moon's disk will be above the horizon every day only from latitudes less than 60°27' (90° − 28°36' – 57' parallax) north or south.

At higher latitudes, there will be a period of at least one day each month when the Moon does not rise, but there will also be a period of at least one day each month when the Moon does not set. This is similar to the seasonal behaviour of the Sun, but with a period of 27.2 days instead of 365 days. Note that a point on the Moon can actually be visible when it is about 34 arc minutes below the horizon, due to atmospheric refraction.

Because of the inclination of the Moon's orbit with respect to the Earth's equator, the Moon is above the horizon at the North and South Pole for almost two weeks every month, even though the Sun is below the horizon for six months at a time. The period from moonrise to moonrise at the poles is a tropical month, about 27.3 days, quite close to the sidereal period. When the Sun is the furthest below the horizon (winter solstice), the Moon will be full when it is at its highest point. When the Moon is in Gemini it will be above the horizon at the North Pole, and when it is in Sagittarius it will be up at the South Pole.

The Moon's light is used by zooplankton in the Arctic when the Sun is below the horizon for months [16] and must have been helpful to the animals that lived in Arctic and Antarctic regions when the climate was warmer.

Scale model Edit

Scale model of the Earth–Moon system: Sizes and distances are to scale. It represents the mean distance of the orbit and the mean radii of both bodies.

About 1000 BC, the Babylonians were the first human civilization known to have kept a consistent record of lunar observations. Clay tablets from that period, which have been found over the territory of present-day Iraq, are inscribed with cuneiform writing recording the times and dates of moonrises and moonsets, the stars that the Moon passed close by, and the time differences between rising and setting of both the Sun and the Moon around the time of the full moon. Babylonian astronomy discovered the three main periods of the Moon's motion and used data analysis to build lunar calendars that extended well into the future. [10] This use of detailed, systematic observations to make predictions based on experimental data may be classified as the first scientific study in human history. However, the Babylonians seem to have lacked any geometrical or physical interpretation of their data, and they could not predict future lunar eclipses (although "warnings" were issued before likely eclipse times).

Ancient Greek astronomers were the first to introduce and analyze mathematical models of the motion of objects in the sky. Ptolemy described lunar motion by using a well-defined geometric model of epicycles and evection. [10]

Sir Isaac Newton was the first to develop a complete theory of motion, mechanics. The observations of the lunar motion were the main test of his theory. [10]

Name Value (days) Definition
Sidereal month 27.321 662 with respect to the distant stars (13.36874634 passes per solar orbit)
Synodic month 29.530 589 with respect to the Sun (phases of the Moon, 12.36874634 passes per solar orbit)
Tropical month 27.321 582 with respect to the vernal point (precesses in

There are several different periods associated with the lunar orbit. [17] The sidereal month is the time it takes to make one complete orbit around Earth with respect to the fixed stars. It is about 27.32 days. The synodic month is the time it takes the Moon to reach the same visual phase. This varies notably throughout the year, [18] but averages around 29.53 days. The synodic period is longer than the sidereal period because the Earth–Moon system moves in its orbit around the Sun during each sidereal month, hence a longer period is required to achieve a similar alignment of Earth, the Sun, and the Moon. The anomalistic month is the time between perigees and is about 27.55 days. The Earth–Moon separation determines the strength of the lunar tide raising force.

The draconic month is the time from ascending node to ascending node. The time between two successive passes of the same ecliptic longitude is called the tropical month. The latter periods are slightly different from the sidereal month.

The average length of a calendar month (a twelfth of a year) is about 30.4 days. This is not a lunar period, though the calendar month is historically related to the visible lunar phase.

The gravitational attraction that the Moon exerts on Earth is the cause of tides in both the ocean and the solid Earth the Sun has a smaller tidal influence. The solid Earth responds quickly to any change in the tidal forcing, the distortion taking the form of an ellipsoid with the high points roughly beneath the Moon and on the opposite side of Earth. This is a result of the high speed of seismic waves within the solid Earth.

However the speed of seismic waves is not infinite and, together with the effect of energy loss within the Earth, this causes a slight delay between the passage of the maximum forcing due to the Moon across and the maximum Earth tide. As the Earth rotates faster than the Moon travels around its orbit, this small angle produces a gravitational torque which slows the Earth and accelerates the Moon in its orbit.

In the case of the ocean tides, the speed of tidal waves in the ocean [19] is far slower than the speed of the Moon's tidal forcing. As a result, the ocean is never in near equilibrium with the tidal forcing. Instead, the forcing generates the long ocean waves which propagate around the ocean basins until eventually losing their energy through turbulence, either in the deep ocean or on shallow continental shelves.

Although the ocean's response is the more complex of the two, it is possible to split the ocean tides into a small ellipsoid term which affects the Moon plus a second term which has no effect. The ocean's ellipsoid term also slows the Earth and accelerates the Moon, but because the ocean dissipates so much tidal energy, the present ocean tides have an order of magnitude greater effect than the solid Earth tides.

Because of the tidal torque, caused by the ellipsoids, some of Earth's angular (or rotational) momentum is gradually being transferred to the rotation of the Earth–Moon pair around their mutual centre of mass, called the barycentre. See tidal acceleration for a more detailed description.

This slightly greater orbital angular momentum causes the Earth–Moon distance to increase at approximately 38 millimetres per year. [20] Conservation of angular momentum means that Earth's axial rotation is gradually slowing, and because of this its day lengthens by approximately 24 microseconds every year (excluding glacial rebound). Both figures are valid only for the current configuration of the continents. Tidal rhythmites from 620 million years ago show that, over hundreds of millions of years, the Moon receded at an average rate of 22 mm (0.87 in) per year (2200 km or 0.56% or the Earth-moon distance per hundred million years) and the day lengthened at an average rate of 12 microseconds per year (or 20 minutes per hundred million years), both about half of their current values.

The present high rate may be due to near resonance between natural ocean frequencies and tidal frequencies. [21] Another explanation is that in the past the Earth rotated much faster, a day possibly lasting only 9 hours on the early Earth. The resulting tidal waves in the ocean would have then been much shorter and it would have been more difficult for the long wavelength tidal forcing to excite the short wavelength tides. [22]

The Moon is gradually receding from Earth into a higher orbit, and calculations suggest that this would continue for about 50 billion years. [23] [24] By that time, Earth and the Moon would be in a mutual spin–orbit resonance or tidal locking, in which the Moon will orbit Earth in about 47 days (currently 27 days), and both the Moon and Earth would rotate around their axes in the same time, always facing each other with the same side. This has already happened to the Moon—the same side always faces Earth—and is also slowly happening to the Earth. However, the slowdown of Earth's rotation is not occurring fast enough for the rotation to lengthen to a month before other effects change the situation: approximately 2.3 billion years from now, the increase of the Sun's radiation will have caused Earth's oceans to evaporate, [25] removing the bulk of the tidal friction and acceleration.

The Moon is in synchronous rotation, meaning that it keeps the same face toward Earth at all times. This synchronous rotation is only true on average because the Moon's orbit has a definite eccentricity. As a result, the angular velocity of the Moon varies as it orbits Earth and hence is not always equal to the Moon's rotational velocity which is more constant. When the Moon is at its perigee, its orbital motion is faster than its rotation. At that time the Moon is a bit ahead in its orbit with respect to its rotation about its axis, and this creates a perspective effect which allows us to see up to eight degrees of longitude of its eastern (right) far side. Conversely, when the Moon reaches its apogee, its orbital motion is slower than its rotation, revealing eight degrees of longitude of its western (left) far side. This is referred to as optical libration in longitude.

The Moon's axis of rotation is inclined by in total 6.7° relative to the normal to the plane of the ecliptic. This leads to a similar perspective effect in the north–south direction that is referred to as optical libration in latitude, which allows one to see almost 7° of latitude beyond the pole on the far side. Finally, because the Moon is only about 60 Earth radii away from Earth's centre of mass, an observer at the equator who observes the Moon throughout the night moves laterally by one Earth diameter. This gives rise to a diurnal libration, which allows one to view an additional one degree's worth of lunar longitude. For the same reason, observers at both of Earth's geographical poles would be able to see one additional degree's worth of libration in latitude.

Besides these "optical librations" caused by the change in perspective for an observer on Earth, there are also "physical librations" which are actual nutations of the direction of the pole of rotation of the Moon in space: but these are very small.

When viewed from the north celestial pole (i.e., from the approximate direction of the star Polaris) the Moon orbits Earth anticlockwise and Earth orbits the Sun anticlockwise, and the Moon and Earth rotate on their own axes anticlockwise.

The right-hand rule can be used to indicate the direction of the angular velocity. If the thumb of the right hand points to the north celestial pole, its fingers curl in the direction that the Moon orbits Earth, Earth orbits the Sun, and the Moon and Earth rotate on their own axes.

In representations of the Solar System, it is common to draw the trajectory of Earth from the point of view of the Sun, and the trajectory of the Moon from the point of view of Earth. This could give the impression that the Moon orbits Earth in such a way that sometimes it goes backwards when viewed from the Sun's perspective. However, because the orbital velocity of the Moon around Earth (1 km/s) is small compared to the orbital velocity of Earth about the Sun (30 km/s), this never happens. There are no rearward loops in the Moon's solar orbit.

Considering the Earth–Moon system as a binary planet, its centre of gravity is within Earth, about 4,671 km (2,902 mi) [27] > or 73.3% of the Earth's radius from the centre of the Earth. This centre of gravity remains on the line between the centres of the Earth and Moon as the Earth completes its diurnal rotation. The path of the Earth–Moon system in its solar orbit is defined as the movement of this mutual centre of gravity around the Sun. Consequently, Earth's centre veers inside and outside the solar orbital path during each synodic month as the Moon moves in its orbit around the common centre of gravity. [28]

The Sun's gravitational effect on the Moon is more than twice that of Earth's on the Moon consequently, the Moon's trajectory is always convex [28] [29] (as seen when looking Sunward at the entire Sun–Earth–Moon system from a great distance outside Earth–Moon solar orbit), and is nowhere concave (from the same perspective) or looped. [26] [28] [30] That is, the region enclosed by the Moon's orbit of the Sun is a convex set.


Observing the Last Quarter Moon

There is a lunar phase that is not as regularly observed as other phases. It is the last (or third) quarter Moon. And the reason for its lack of scrutiny by casual stargazers is because it generally rises around midnight. Although space does not permit me to review the reason for the cycle of lunar phases, you can refresh your understanding by visiting http://www.theskyscrapers.org/the-moon-its-just-a-phase-its-going-through.

March’s last quarter Moon will occur on the 20th, so this month’s column will highlight a few of the features that can be observed during this often overlooked phase. A small inexpensive telescope will be required to observe these formations adequately, though binoculars or even a birder’s spotting scope will provide glimpses of a few of them.

Even around the midnight hour you’ll need to wait for the moon to ascend higher into the sky and above the tree line. But if you don’t wish to forgo your beauty sleep, the next best time to observe this phase is a couple of hours before morning twilight. At sunrise the last quarter Moon will be due south of your location and at its highest point off the horizon. You can easily observe the moon in broad daylight, but the contrast is low, causing fewer details to be seen.

The accompanying Moon map will help you locate the lunar features I will explore. The Moon’s north pole is at the top of the map, while its western limb is to the left. Keep in mind that binoculars will provide you the same view that the map shows. Various telescope designs reverse the image right to left and up and down. You’ll need to orient your telescopic view to the map using a prominent surface feature as a guide.

There are many formations that can be observed during this lunar phase. And even if you have observed some of them during a different phase of illumination, the ever changing sunlight angle can reveal subtle details not seen in those other phases.

Also, most native Rhode Islanders know that our state is often used as a unit of measure. Refer to the inset of the Rhode Island state map to scale in the un-illuminated half of the moon map. East to west “Little Rhody” is approximately 37 miles across, and the north to south dimension measures 48 miles. Keep these figures in mind when comparing to crater sizes.

On the edge of Mare Imbrium (translation means Sea of Rains – yes, early astronomers once thought the Moon possessed seas and oceans) is the crater Archimedes, an almost perfect circle about 52 miles across. Under low magnification its floor is almost featureless. A short distance to the southeast and seeming to extend from the terminator (during Last Quarter the terminator defines the sunset point) is the Apennine Mountains. This range contains some of the tallest mountains on the lunar surface. Carefully scan up and down this region. Some of the mountains’ bases may already be in shadow while their peaks can still be catching glimpses of sunlight.

As we continue our journey south and to the west we encounter the absolutely beautiful crater Copernicus. While this crater is not the largest (only 53 miles across), the detail one can observe is remarkable. Its walls show very fine detail and the crater floor has an incredible central peak. In fact, during one perfect evening many moons ago while using the 8 ¼-inch Clark refractor at Seagrave Observatory, I was able to look deep into this crater and see where a huge boulder had tumbled down one of its steep walls. Outstanding!

Next please locate and examine the crater chain that comprises Ptolemaeus, Alphonsus and Arzachel. The detail that can be seen here is exquisite. Ptolemaeus is an old crater about 95 miles in diameter. Another impact, Herschel, blasted a 25-mile-in-diameter hole into its northern rim, and Ptolemaeus also shows smaller impacts on its floor. Alphonsus, 74 miles across, has a well- preserved central peak, where Ptolemaeus does not. Arzachel is roughly 60 miles in diameter and is very well preserved, showing great detail in its walls and central peak.

One of the most fascinating features on the lunar surface is the Straight Wall. This feature lies to the southwest of Arzachel and sits in Mare Nubium (Sea of Clouds). This formation is very impressive. It is a fault or escarpment approximately 68 miles long, 1.5 miles wide, and no more than 1,000 feet above the floor of the Mare. While it may look very steep, its slope is no more than 7 degrees. The Straight Wall’s appearance changes dramatically with the sun angle, so try to observe it during other lunar phases as well.

And finally I can’t end this lunar tour without noting crater Clavius. Sci-fi fans will recall that the monolith in the movie 2001: A Space Odyssey was uncovered in this crater. Clavius is huge, measuring 140 miles across. Though several smaller impacts have marred its floor, the inner crater walls are high and well defined. Several impacts have also occurred along the rim.

I hope this brief tour of our closest neighbor in space will encourage you to spend a few hours examining the lunar surface with whatever optical instrument you can use. The more magnification one is able to apply, the more detail one will be able to discern. Binoculars and telescopes should be outside collecting moonlight, not inside collecting dust in a closet or basement.

In conclusion, don’t forget we set our clocks ahead one hour (spring ahead) to EDT (Eastern Daylight Time) on Sunday morning, March 12, at 2:00 a.m. On this date most of the United States shifts to Daylight Saving Time. And finally, on the same day as the last quarter moon (March 20), the Vernal Equinox (spring) begins at 6:29 a.m. EDT. The Sun appears to be moving northward in our sky as a result of the Earth’s axial tilt as we revolve around the Sun on our axis.

The only observatory you may often find open after midnight to observe the last quarter Moon is Frosty Drew Observatory in Charlestown, open every clear Friday night year-round. However, don’t forget that the other observatories are open at more convenient times to observe the heavens. Seagrave Memorial Observatory in North Scituate is open to the public every clear Saturday night. Ladd Observatory in Providence is open every clear Tuesday night. The Margaret M. Jacoby Observatory at the CCRI Knight Campus in Warwick is open every clear Wednesday night.

Great American Total Solar Eclipse on August 21, 2017. Countdown: 172 days as of March 1, 2017.


5 Facts Everyone Must Know Now That The Solstice Is Over

As the year draws to a close, we approach a very special time of year, at least from an astronomical perspective. This past Thursday, December 21st, marked the Winter Solstice in the Northern Hemisphere, or the date where the Earth’s axis is tilted its maximal amount away from the Sun, as viewed from an observer north of the equator. Sure, it’s pretty common knowledge that the Earth’s revolution around the Sun in conjunction with its axial tilt is the reason for the seasons. But the December solstice — one of the two days where the Earth’s tilt is maximally inclined with respect to the Sun — brings a number of special things along with it that are unique to this time of year. Here are the top 5.

1.) A dedicated astrophotographer living North of the Arctic Circle could take the first-ever 360-degree star trail photo!

Never-yet-accomplished, Lewin’s Challenge requires 24 hours of consecutive darkness, something that happens for six continuous months, centered on the solstices, at each of the poles. As we cycle through our orbit, the equinoxes mark a time when every location on Earth receives 12 hours of daylight and 12 hours of night. Subsequently, one of the poles plunges into darkness, with progressively lower and lower (numbered) latitudes surrounding that pole joining the party. This reaches its peak on the Solstice, where all latitudes within 23.5 degrees of the pole-in-darkness (so everyone north of 66.5 degrees on Saturday’s Solstice) will receive 24 hours of sunless skies. If you’re far enough north, you’ll spend that entire time with stars visible, and in darkness, as well.

If you can get inside the Arctic circle, have clear skies, and leave your shutter open, properly centered on the North Pole, you could be the first one! Anyone in (or north of) Cornwallis Island, Canada, Longyearbyen, Norway, or Qaanaaq, Greenland, willing to give it a shot?

2.) Anyone living north of the 43rd parallel will, on the Winter Solstice, never have the Sun rise higher in the sky than it appears all day at the South Pole!

That’s right, the South Pole — one of our favorite metaphors for a cold, dark, remote place — will have the Sun be higher above the horizon all day than locations like Madison, WI, Portland, OR, all of Germany, Poland, England and nearly all of Russia will see at any time during the day! In fact, for a modest location like Portland, OR, with a latitude of 45.6 degrees N, it will take around a week for the Sun to reach an angle above the horizon that exceeds what you’d see at the South Pole, while for an observer in Anchorage, AK, that won’t happen for another six weeks!

3.) The Winter Solstice now occurs very close to perihelion, or the Earth’s closest position to the Sun, but that is slowly changing over time!

The Earth’s orbit around the Sun makes an almost perfect ellipse, making a complete revolution every year. Well, kind of. You see, there are two types of year: the tropical year, which we define as 365 (or sometimes 366) days, and is the amount of time it takes the Sun to return to the same position it was in the sky approximately one revolution ago, and the sidereal year, which is the amount of time it takes the Earth to return to the same location in space, relative to the background of stars, that it was exactly one revolution ago.

These two measurements of years are slightly different from one another, by one part in about 26,000 combined with the smaller intrinsic precession of Earth’s orbit with respect to the stars (mostly due to the other planets), we get that the Winter Solstice cycles through an entire orbit every 21,000 years. The Winter Solstice coincided with perihelion — which now occurs just a couple of weeks later — just a short 800 years ago, and has been progressively migrating away from it in about 10,000 years, it will be coincident with aphelion, or the point of farthest distance from the Sun! This past Thursday’s Winter Solstice was the closest solstice to the Sun you’ll ever experience for the rest of your life!

4.) The low position of the Sun in the sky means that the full Moon closest to the Solstice, at its highest, will be the highest full Moon above the horizon all year!

Think about it when the Earth’s axis is maximally tilted towards the Sun and the Moon is full — as in, on the other side of the Earth from the Sun — that means the Earth’s axis will be maximally tilted away from the Moon. (To within a maximum error of just 5 degrees, the amount that the Earth-Moon orbital plane is inclined to the Earth-Sun plane.) That means, in a broad sense, that just as the Sun appears to carve its lowest paths through the sky, the full Moons closest to your Winter Solstice carve their highest paths through the sky, and vice versa during the Summer Solstice!

This also means the new Moons closest to the Winter Solstice carve their lowest paths through the sky, and since the new Moon falls close to the Solstice this year, it will be just as low on the horizon as the Sun. Of course, those of you in the Southern Hemisphere will find quite high new Moons and low full Moons as a result at this time of year: exactly the opposite of what those of us in the north will see!

So while Australians are enjoying the Sun riding its highest paths through the sky, here in the north — both two weeks ago and two weeks past the solstice — we’ll enjoy the full Moon, which happens to be a supermoon, doing the same thing!

5.) It’s called the “solstice” because the Sun literally “stands still” in the sky.

For approximately a week in each direction around both solstices, the path of the Sun through the sky barely changes at all for all observers in both hemispheres. As such, our word for solstice marks exactly that occurrence, and explains why, if you track the Sun’s path on a daily basis over the course of a year, you’ll see nearly identical tracks near the bottom (marking the Winter Solstice) and the top (marking the Summer Solstice) of all such images.

There is a theory that the whole idea of celebrating the new year only began as humans migrated away from the equator, where the difference between the Sun’s path through the sky — and the seasonal climates — became incredibly different. As the Winter Solstice approaches, the Sun’s path dips lower and lower each day. Perhaps you’d fear, if you didn’t know any better, that it might drop below the horizon entirely and disappear forever. But the Solstice marks its minimum point, and then a few days afterwards, it noticeably begins to rise again. Hence, the Sun would return to its dazzling spring-and-summer heights, and a new year would begin. Perhaps that’s where rituals such as New Year’s, Christmas, and other just-post-solstice “rebirth” celebrations owe their origins to!

And there’s a special solstice bonus for those of you who care about humanity’s ventures to journey into space.

6.) It was on the Winter Solstice in 1968 that humans, for the first time, were launched to the Moon!

The Apollo 8 mission, the first manned mission to reach and orbit the Moon, was launched on the Winter Solstice in 1968, exactly 46 years ago this Sunday. The first humans to ever see the Earth from such a great distance, Frank Borman, Jim Lovell and Bill Anders began their journey away from Earth on the Winter Solstice, the darkest evening of the year.

Three days later, they plunged behind the Moon, and both the Sun and the Earth became invisible for a few hours. When those few hours passed, first the Sun and then the Earth re-emerged over the limb of the Moon. This was what they saw.

As Bill Anders said almost immediately,

“We came all this way to explore the Moon, and the most important thing is that we discovered the Earth.”

So enjoy the solstice however you see fit, and as you do, try and remember this: whether you’re bathed in the longest day or the longest night of the year, there are some things that we all have in common and can bring us all together. The story of where we are and how we came to be here — on Earth, in the Solar System and in the Universe — just might be the most omnipresent of them all.


Conclusion

Here and in my previous discussion I have only scratched the surface of what can be said in response to the flat earth nonsense that is so pervasive today. With time, I will revisit this topic. Skiba chided me for not addressing supposed biblical passages that teach that the earth is flat. If I had dealt with that first, Skiba probably would have criticized me for not dealing with the supposed physical evidence. I am working on a response to what he and others claim the Bible teaches, which I will share eventually. Stay tuned.