Astronomy

Recognising lunar month only by looking the sky

Recognising lunar month only by looking the sky


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Suppose somebody went on an island and don't have sense about time, dates, months. The only thing he has is seeing the sky. Is it possible to recognise which lunar month it is by just looking the sky? I ask this because I know how to see beginning of the lunar month, but how to recognise which month is it? So we can look at the Sun, Moon, the stars. Is there a way to figure that out?


Not easily.

The Lunar Islamic calendar is based on a strict succession of months, with each month based only on the position of the moon, and no intercalated months or months extended to 31 days in order to keep the cycle of months aligned with the solar year. The start of the months are determined by the moon, the names of the months are not defined by any astronomical feature.

So to determine which Islamic month it is you need to know the actual amount of time that has passed. Now the positions of the planets change day by day, and by careful observation of the planets, and given a detailed ephemeris of their positions, one could work out the exact date, and therefore the Islamic month.

This is similar to determining the day of the week by astronomical observations, since the start of the day is based on the motion of the sun, but the name of the day is not defined on any astronomical feature.


Lengths of lunar months 2021

What is a lunar month? It’s the duration between successive new moons. Also called a lunation or synodic month, it has a mean period of 29.53059 days (29 days 12 hours and 44 minutes). That’s the mean, but the the true length varies throughout the year.

Quite by coincidence, the lunar month straddling 2020 and 2021 – between the new moons of December 14, 2020, and January 13, 2021 – matches the mean lunar month of 29 days 12 hours and 44 minutes. The lunar month almost never equals the mean lunar month in duration. Most of the time, the true lunar month is either longer or shorter than the mean.

Keep reading to learn more about the lengths of lunar months in 2021.

Lengths of the lunar months in 2021

Successive new moons Length of lunar month
Dec 14, 2020, to Jan 13, 2021 29 days 12 hours 44 min
Jan 13 to Feb 11 29 days 14 hours 06 min
Feb 11 to Mar 13 29 days 15 hours 15 min
Mar 13 to Apr 12 29 days 16 hours 10 min
Apr 12 to May 11 29 days 16 hours 29 min
May 11 to Jun 10 29 days 15 hours 53 min
Jun 10 to Jul 9 29 days 14 hours 24 min
Jul 9 to Aug 8 29 days 12 hours 34 min
Aug 8 to Sep 6 29 days 11 hours 02 min
Sep 6 to Oct 6 29 days 10 hours 14 min
Oct 6 to Nov 4 29 days 10 hours 09 min
Nov 4 to Dec 4 29 days 10 hours 28 min
Dec 4, 2021, to Jan 2, 2022 29 days 10 hours 50 min

One lunar month is the period of time from new moon to new moon. As viewed from the north side of the Earth’s and moon’s orbital planes, the Earth goes counterclockwise around the sun and the moon goes counterclockwise around Earth. Image via Wikipedia.

Why are the lunar months different lengths? In a nutshell, the longest lunar month occurs when the successive new moons coincide closely with lunar apogee, the moon’s farthest point from Earth in its orbit.

In contrast, the year’s shortest lunar month takes place when the successive new moons fall appreciably close to lunar perigee – the moon’s closest point to Earth in its orbit.

On the average, the lunar month (new moon to new moon) is about 2.22 days longer than the sidereal month (one complete revolution of the moon relative to the background stars). However, if the moon is near apogee at the end of one sidereal month, the moon travels more slowly than average in its orbit. Therefore, the period of time between the end of the sidereal month and the end of the lunar month is longer than average.

The opposite is the case when the new moon is near perigee. The moon travels more swiftly in its orbit at perigee, in which case the time period between the end of the sidereal month and the end of the lunar month is less than average.

The most extreme longest lunar months happen when successive new moons occur near lunar apogee – and in addition, when Earth is near perihelion (its closest point to the sun). Because Earth is always closest to the sun in early January, the very longest lunar months take place between December and January new moons.

On the other hand, extremely short lunar months happen when successive new moons fall near lunar perigee – and in addition, the Earth is near aphelion (Earth’s farthest point from the sun in its orbit). Because Earth is always at aphelion in early July, the very shortest lunar months take place between June and July new moons.

The variation in the length of lunar months happens because the moon’s orbit around Earth is not a perfect circle. However, it is very nearly circular, as the above diagram shows. Diagram by Brian Koberlein.

When are the longest and shortest lunar months of the 21st century? The longest lunar month of the 21st century (2001 to 2100) occurs between the December 2017 and January 2018 new moons. With a length of 29 days 19 hours and 47 minutes, this particular lunar month exceeds the mean by a whopping 7 hours and 3 minutes.

The century’s shortest lunar month takes place between the new moons of June and July 2053, a period of 29 days 6 hours and 35 minutes. That’s 6 hours and 9 minutes shorter than the mean.

Incidentally, exceptionally long or short lunar months repeat in cycles of 9 years.

Phases of the moon, posted to EarthSky Facebook by our friend Jacob Baker.


May 23rd: Back On The Sky & Exploring The Lunar South Pole

Description: Today’s 2 topics:

  • After six weeks of clouds, thunder, rain, hail, and lightning asteroid hunters are glad to be on the sky again.
  • The Indian Space Research Organization has placed a spacecraft, Chandrayaan-2, in lunar orbit where it is sending back images of our Moon from less than a distance of 2,000 miles. This project is an ambitious mission to land a rover near the Moon’s south pole.

Bio: Dr. Al Grauer is currently an observing member of the Catalina Sky Survey Team at the University of Arizona. This group has discovered nearly half of the Earth approaching objects known to exist. He received a PhD in Physics in 1971 and has been an observational Astronomer for 43 years. He retired as a University Professor after 39 years of interacting with students. He has conducted research projects using telescopes in Arizona, Chile, Australia, Hawaii, Louisiana, and Georgia with funding from NSF and NASA.

He is noted as Co-discoverer of comet P/2010 TO20 Linear-Grauer, Discoverer of comet C/2009 U5 Grauer and has asteroid 18871 Grauer named for him.

Today’s sponsor: Big thanks to our Patreon supporters this month: David Bowes, Dustin A Ruoff, Brett Duane, Kim Hay, Nik Whitehead, Timo Sievänen, Michael Freedman, Paul Fischer, Rani Bush, Karl Bewley, Joko Danar, Steven Emert, Frank Tippin, Steven Jansen, Barbara Geier, Don Swartwout, James K. Wood, Katrina Ince, Michael Lewinger, Phyllis Simon Foster, Nicolo DePierro, Tim Smith, Frank Frankovic, Steve Nerlich

Please consider sponsoring a day or two. Just click on the “Donate” button on the lower left side of this webpage, or contact us at [email protected]

557: Back On The Sky

In the American southwest we welcome the Monsoon rainy season during which the Earth receives much needed moisture. Asteroid hunters use this break from observing to install new equipment and do annual maintenance to keep our telescopes in tip top shape. This year we added new adjustable stand up /sit down desks to help us survive 13 hour long winter nights.

After six weeks of clouds, thunder, rain, hail, and lightning asteroid hunters are glad to be on the sky again. Taking advantage of the improved weather conditions my Catalina Sky Survey team captain Eric Christensen pointed our 60 inch telescope into the Constellation of Boötes and was rewarded by the discovery of four new space rocks. Of these 2019 QK quickly received enough followup observations for scientists at the Minor Planet Center to estimate its size and path about the Sun. Turns out that this 715 foot diameter space rock has an orbit which never takes it closer to us than about one third of our distance from the Sun. Even so, this discovery marks the beginning of a new asteroid hunting season in Arizona.

Using our excellent location, my team the Catalina Sky Survey scans the sky with four telescopes, 24 nights per month when the Moon is not too bright from the Catalina Mountains north of Tucson, Arizona. Our goal is to find any celestial neighbors whose impact could pose a threat to residents of Planet Earth. Along the way we discover thousands of new main belt asteroids and a few comets.

558: Exploring The Lunar South Pole

The race to explore the Moon by robots and eventually human lunar colonists is on. The Indian Space Research Organization has placed a spacecraft, Chandrayaan-2, in lunar orbit where it is sending back images of our Moon from less than a distance of 2,000 miles. This project is an ambitious mission to land a rover near the Moon’s south pole.

This wild lunar region has a mountain, Epsilon Peak, 29,600 feet high, deep basins, and a temperature of minus 13 Celsius or about 8 degrees above zero Fahrenheit. So far orbiters from several countries have studied the lunar south polar region. The NASA Lunar Crater Observation and Sensing Satellite found water in the plume of debris created by the impact of its Centaur launch vehicle into a permanently shadowed south lunar pole crater bottom. Crater rims in the lunar south polar region receive nearly constant sunshine which could to power solar panels. Additionally at the bottom of these craters are cold traps which are in constant shadow and possess water ice and other volatiles left there during the early history of the solar system.

Near the lunar south pole human space colonists could use solar energy to power equipment and keep warm, manufacture needed items, and most importantly have water to drink as well as to use a raw material. Applying electricity to water produces Oxygen to breathe and Oxygen and Hydrogen which is a handy rocket and rover fuel. When humans will show up is only a guess.

For Travelers in the Night this is Dr. Al Grauer.

End of podcast:

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Submitting for Certification

To receive your Lunar Program Certificate and award pin, simply send your observations along with your name, mailing address, email, phone number, club affiliation, and whom to send the certification either to an officer of your astronomy club for review and approval, or to the Lunar Observing Program Coordinator.

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Calendars: Where Ancient Astronomy Meets The Modern World

When we think about astronomy, there arise some questions such as, what is the role of astronomy in everyday life, and what was its role Among ancient civilizations? Well, let’s discuss some facts related to it.

Imagine 50,000 years ago, to keep agricultural timekeeping and the provision of crops for growing societies, people wanted to keep track of time. They used the sky to keep time and to track the seasonal cycle and also they observed the solar and lunar cycle. As the most prominent objects in the sky, they monitored the phases of both the sun and the moon. Also, they noticed the strange juxtapositions of both. What would they have made using these phenomena? They found out that the sky was a map, a calendar, a clock, and also a source of myth and legend.

Among these, the calendar is a topic where ancient astronomical practices meet the modern world. So, let’s look at calendars or timekeeping, and see how ancient astronomical practices are deeply embedded in our modern life. Astronomy still lives with us every day on our calendar.

José A. Peñas/SINC

As we know, there are four major subdivisions of time in a year where three of them are astronomical. The days – the rotation period of the Earth, the year – the orbital period of the Earth around the Sun, and the month – is a lunar cycle or the orbital period of the moon around the Earth. The only division of time that’s not naturally or obviously astronomical is the week.

Actually, the week did not have the same division of time (ranges from 4-10 days) across different cultures all around the world. The classic week of the modern calendar, that is 7 days, starts with the Babylonians and the Egyptians. The names of the days of the week are quite obviously the names of seven moving objects in the night and daytime sky, the Sun, the Moon, and the five naked-eye visible planets Mercury, Venus, Mars, Jupiter, and Saturn in Roman language like French, or Spanish, or Italian, or Portuguese. So, the week is also an astronomical relic.

ORIGIN OF MODERN CALENDAR

Our calendar traces back to the ancient Romans in the seventh century BC. Rome was a set of warring tribes, quite militaristic, that dominated their region, and occasionally would do battle with other tribes North of the Alps. They needed a calendar. So, the ancient Romans started their year when the snow melted enough that they could raise an army and do battle. They were following roughly a lunar calendar and they only needed 10 months in their year and reset it again.

They didn’t count the time in the dark winter. That’s why the last four months of our year are named after the Roman words for seven, eight, nine, and ten. This calendar was used for a few centuries. Then the Emperor Promiscuous and other Emperors decided to add a couple of light months at the front end, giving 12 months. Thus, the year their lunar calendar consisted of 12 lunar cycles, that is 354 days. That is, the world’s first calendars were lunar calendars!

Aurignacian Lunar Calendar / diagram, drawing after Marshack, A. 1970 Notation dans les Gravures du Paléolithique Supérieur, Bordeaux, Delmas / Don’s Maps

The actual problem with the lunar calendar was, it was not good for knowing about seasons. Because it goes out of sync by 11 days a year as compared to the solar cycle. The Romans needed their calendar to be season reliable. Thus the solar calendar was introduced.

The solar calendar – the time taken by the Earth to go around one complete orbit of the Sun. So, the calendar moves towards 365 days and a quarter day. It consisted of 12 months. They had a pretty strictly alternating sequence of 30 and 31 days among the later months. As a relic, February was the short month, the unlucky month. The last months of the year named after numbers, and the first months of the year named after primordial gods such as Maya for May, Janus for January, the god of doorways and beginnings etc.

Do you wonder, while we’re using the knuckles of our hand to figure out which days have 30 and 31 days, July and August have the same knuckle and have 31 days?

During the time of Julius Caesar, he presided over one of the most extensive and powerful regimes ever known in world history. For regulating this large empire and for administrative purposes he needed a good calendar. Caesar recognized that the old Roman calendar was not up to good for this. So, he put forward the Julian calendar. The main thing Caesar added in calendars was a leap year, that is an extra day in every fourth year, giving a calendar with a mean length of 365.25 days. That’s close to a solar cycle. Also, he decided to take the first unnamed month in sequence and name it after himself, hence July.

After Caesar, Augustus didn’t make any innovation to the calendar. But due to his large ego, he named the next unnamed month after himself, hence August. Also, since Julius Caesar’s month was longer than his month, he added an extra day to his month, and hence messed up the pattern.

The Julian calendar is quite successful. However, the exact time that the Earth to rotate around the sun is 100th of a day different from 365.25. It’s actually 365.24199. So, Julian’s calendar gets out of sync by the 100th of a day per year. After a century, that’s a day. By medieval times, the Julian calendar was off by a week or so, and agricultural planting cycles were starting to be affected. So, in the era of the Italian Renaissance, the last adjustment to the modern calendar was made by the Popes. Pope Gregory recognized the problem with the calendar. He with the help of some astronomers made careful measurements of the length of the day and the year and made a final adjustment to our calendars. The Gregorian calendar only off by less than a ten-thousandth of a day per year, and therefore will be good for tens of millennia. This leads to the rise of the modern calendar.

Detail of the tomb of Pope Gregory XIII celebrating the introduction of the Gregorian calendar.

An interesting sidelight on this is that the Protestant countries after the Reformation, did not follow the Pope’s guidance on the calendar, so they resisted to make the adjustment that Gregory made for another 150 or 200 years. In France, this happened quickly. But in England and the United States where Protestants were dominant, the calendar was not adjusted until the gap between the solar year and the calendar year had approached 13 days. So, due to this, when they decided to follow the Gregorian calendar on one day, April fourth turned into April 15th. Benjamin Franklin wrote in Poor Richard’s Almanack, Do not fret over the loss of those days”. But people worried that they’d be ripped off rent, and bad things would happen although the Earth continued in its orbit. Thus, the French created the April Fool holiday to mock the Americans and the British for taking so long to get the right calendar. So, calendars have been part of our culture for a long time.

Calendars and their history gives us a quirky and entertaining embedding of astronomy in modern culture. According to a recent survey, there are about forty calendars used in the world today. Most of them are astronomical. The common theme of the calendar is the desire to organize units of time to satisfy the needs and preoccupations of society. Also, this process of organization provides a sense of understanding and controlling time itself. Thus our calendars serve as a link between humankind and the cosmos or calendars are the topics where ancient astronomy meets the modern world.


How to Use a Moon Map

Every one of these moon facts and features takes on its own individuality and meaning if you know its name. To do that, you'll need a Moon map and a flashlight to read it by. Many astronomy books include Moon maps, or you can buy one on our online store. But you’ll need to know a trick or two to compare the map with what you see in the eyepiece — so read on with these moon facts and moon-viewing techniques.

Most maps show the Moon oriented more or less how you’ll see it with the unaided eye or binoculars: with its north side up. But here’s the tricky part. Many telescopes give an upside-down view, and many give a mirror-image view. Some telescopes do both. These two effects are entirely separate from each other, and you need to deal with them separately.

If you have a reflector telescope, or a refractor that you’re viewing “straight through” (in a straight line from end to end), you’ll see an ordinary, non-mirror image: a correct image. If you’re using a telescope where the eyepiece fits into a right-angle attachment (a star diagonal), a mirror image is probably what you’ll see. To check, aim the telescope at a billboard or street sign during the daytime. Twist your head around so the sign appears more or less right-side up, and you’ll see right away whether you’re looking at correct writing or mirror writing.

If you have a correct image, simply turn the Moon map around until its mare patterns match the patterns you see. (Never mind if the printing is upside down or at some weird angle.) You can now compare the map directly to the view in the telescope.

If you have a mirror image, you’ll have to mentally flip the Moon in your eyepiece right-for-left to match the Moon on paper. Alternatively, you can buy a mirror-image Moon map. Small maps like these identify only a few of the thousands of lunar features revealed in an amateur telescope.

The next step is Antonín Rükl’s larger Field Map of the Moon or — for true lunar enthusiasts — our highly detailed and beautiful Moon globe, a three-dimensional representation of the moon created with 15,000 actual images from NASA's Lunar Reconnaissance Orbiter.

And because you've read these moon facts so far, here's a special treat: NASA's animation of the entire 4.5-billion-year history of the moon boiled down into 2.6 minutes:


2016’s longest lunar month starts October 30

What is a lunar month? It’s the duration between successive new moons. Also called a lunation or synodic month, it has a mean period of 29.53059 days (29 days 12 hours and 44 minutes). That’s the mean, but the the actual length varies throughout the year. The lunar month beginning on October 30, 2016 is the longest lunar month of 2016. It lasts for 29 days 18 hours and 40 minutes, until November 30.

That’s 5 hours and 56 minutes longer than the mean.

And it’s 11 hours and 20 minutes longer than 2016’s shortest lunar month, which happened between the new moons of May 6 and June 5.

Follow the links below to learn more:

Lengths of the lunar months in 2016

February 8 to March 9 29 days 11 hours 16 min March 9 to April 7 29 days 09 hours 29 min

One lunar month is the period of time from new moon to new moon. As viewed from the north side of The Earth’s and moon’s orbital planes, the Earth goes counterclockwise around the sun and the moon goes counterclockwise around Earth. Image via Wikipedia

Why are the lunar months different lengths? In a nutshell, the longest lunar month of the year occurs when the successive new moons coincide closely with lunar apogee – the moon’s farthest point from Earth in its orbit. The lunar month beginning October 30, 2016 starts at 1738 UTC, with the instant of new moon (when the moon is most nearly between the Earth and sun for this month). Apogee is just over a day later, on October 31 at about 19 UTC. Translate UTC to your time zone here.

In contrast, the year’s shortest lunar month takes place when the successive new moons fall appreciably close to lunar perigee – the moon’s closest point to Earth in its orbit.

On the average, the lunar month (new moon to new moon) is about 2.22 days longer than the sidereal month (one complete revolution of the moon relative to the background stars). However, if the moon is near apogee at the end of one sidereal month, the moon travels more slowly than average in its orbit. Therefore, the period of time between the end of the sidereal month and the end of the lunar month is longer than average.

The opposite is the case when the moon is near perigee. The moon travels more swiftly in its orbit at perigee, in which case the time period between the end of the sidereal month and the end of the lunar month is less than average.

Believe it or not, the year’s longest and shortest lunar months don’t showcase ultimate extremes. In fact, the few years ahead (2017 and 2018) will stage shorter and longer lunar months that vary even more greatly from each other and the mean than those of 2016.

The most extreme longest lunar months happen when successive new moons occur near lunar apogee – and in addition, when Earth is near perihelion (its closest point to the sun). Because Earth is always closest to the sun in early January, the very longest lunar months take place in between December and January new moons.

On the other hand, extremely short lunar months happen when successive new moons fall near lunar perigee – and in addition, the Earth is near aphelion (Earth’s farthest point from the sun in its orbit). Because Earth is always at aphelion in early July, the very shortest lunar months take place in between June and July new moons.

The variation in the length of lunar months happens because the moon’s orbit around Earth is not a perfect circle. However, it is very nearly circular, as the above diagram shows. Diagram by Brian Koberlein.

When are the longest and shortest lunar months of 21st century? The longest lunar month of the 21st century (2001 to 2100) occurs in between the December 2017 and January 2018 new moons. With a length of 29 days 19 hours and 47 minutes, this particular lunar month exceeds the mean by a whopping 7 hours and 3 minutes.

The century’s shortest lunar month takes place in between the new moons of June and July 2053, a period of 29 days 6 hours and 35 minutes. That’s 6 hours and 9 minutes shorter than the mean.

Incidentally, exceptionally long or short lunar months repeat in cycles of 9 years.

Each year, the shortest and longest lunar months come later in the year. For instance, in 2017, the shortest lunar month happens in between the May 25 and June 24 new moons and the longest one in between the December 18, 2017 and January 17, 2018 new moons. Click here for a complete listing for the length of each lunar month in the 21st century.

Phases of the moon, posted to EarthSky Facebook by our friend Jacob Baker.

Bottom line: October 30, 2016 marks the start of the longest lunar month of 2016. It lasts for 29 days 18 hours and 40 minutes. That’s 5 hours and 56 minutes longer than the mean. And it’s 11 hours and 20 minutes longer than 2016’s shortest lunar month, which spanned a period between early May and early June.


This Week’s Night Sky: Watch a ‘Lite’ Lunar Eclipse

Look for the moon to darken a smidge as it moves through Earth's shadow, and hunt for a comet passing by a spiral galaxy.

Moon and Greedy Jupiter. As dusk settles in on Monday, March 21, get outside and face east to see the moon and a bright star-like Jupiter rise together into the night sky.

The two super-bright objects will appear quite close—only two degrees apart, a little more than the width of your thumb held at arm’s length.

Try your hand at viewing Jupiter and its four largest moons, which are lined up on either side of the giant planet. Jupiter is so large that it could easily swallow over 1200 Earth-sized worlds.

Earlier this month a new study was released suggesting that in the early part of of the solar system’s history, a baby Jupiter may have traveled through the inner solar system and swallowed up much of the primordial, planet-building material. This could explain why planets close to the sun—Mercury, Venus, Earth and Mars—are all on the small side.

Hungry Jupiter may have swept the inner solar system so efficiently that it prevented other large rocky planets from forming closer to the sun than Mercury.

Faint Lunar Eclipse. With the full moon on the night of Tuesday, March 22 look for a faint eclipse of the moon.

Lunar eclipses occur when the Sun, Earth and moon align such that Earth’s own shadow is cast on the surface of the moon, darkening it. This week’s event is called a penumbral lunar eclipse, and skywatchers will see 78 percent of the moon’s southern parts skirt through the outer, faint shadow cone of Earth.

The effect will be fairly subtle, but keen observers with clear skies should see a slight darkening of the moon’s otherwise highly reflective silvery surface.

The eclipse will start at 2:39 a.m. PDT and will be best visible in western North America at 4:47 a.m. PDT, when it reaches its deepest and darkest point. Folks in the eastern part of the continent will miss out on the second half of the sky show, since the moon will be setting in the west near sunrise. Meanwhile observers in the Pacific Ocean, Australia, New Zealand and Japan can catch the entire eclipse in their evening of March 23, with the darkest phase occurring at 11:47 UT.

Moon and Spica. Late night Thursday, March 24, and into the early morning hours of Friday, look for the nearly full moon and the bright blue star Spica to dominate the entire night as they rise in the east and travel high in the south until dawn.

Look to the upper right of the pair for the bright orange star Arcturus, and the planet Jupiter perched to their upper right.

Comet Galaxy Pair. Here’s a wonderful observing challenge and photo opportunity for those with telescopes. On the night of Thursday, March 24, Comet Ikeya-Murakami (P/2010 V1) swings through the bright constellation Leo the Lion, near the pretty spiral galaxy NGC 2903.

The pair will be less than a degree apart, allowing them to both fit into the same field of view through a telescope using high magnification. Both will appear as ghostly grey puff-balls, and the comet may sport a faint tail visible as a streak of light.

NGC 2903 is a spiral galaxy that shines at magnitude 8.9, making it one of the brighter galaxies visible to backyard telescopes. This giant island of stars lies 32 million light-years from Earth and is face-on to us, allowing us to see its dust lanes and the bright knots in its spiral arms.

Follow Andrew Fazekas, the Night Sky Guy, on Twitter, Facebook, and his website.


Recognising lunar month only by looking the sky - Astronomy

The EJS Lunar Month JS model displays the appearance of the Moon over the course of the lunar (synodic) month. The window shows the appearance of the Moon as seen from Earth as well as the current number of days into the lunar month and the current Moon phase.

The EJS Lunar Month JS model was developed using the Easy Java/JavaScript Simulations (EjsS) version 5. It is distributed as a ready-to-run html page and requires only a browser with JavaScript support. This model runs on tablets.

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AAAS Benchmark Alignments (2008 Version)

4. The Physical Setting

  • K-2: 4A/P2. The sun can be seen only in the daytime, but the moon can be seen sometimes at night and sometimes during the day. The sun, moon, and stars all appear to move slowly across the sky.
  • K-2: 4A/P3. The moon looks a little different every day but looks the same again about every four weeks.
  • 6-8: 4B/M5. The moon's orbit around the earth once in about 28 days changes what part of the moon is lighted by the sun and how much of that part can be seen from the earth- the phases of the moon.

11. Common Themes

  • 6-8: 11B/M1. Models are often used to think about processes that happen too slowly, too quickly, or on too small a scale to observe directly. They are also used for processes that are too vast, too complex, or too dangerous to study.

NSES Content Standards

NSES Professional Development Standards

  • Active Investigation: Involve teachers in actively investigating phenomena that can be studied scientifically, interpreting results, and making sense of findings consistent with currently accepted scientific understanding.

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Recognising lunar month only by looking the sky - Astronomy

I recently asked my readers to send me their questions about astrology – what confuses them? What would they like to know more about? Nearly every response was about house systems. Why are there so many of them? Which one is best? Which one am I using, and why?

What are houses?

irst, an explanation of what they are in the first place. An astrology chart is a symbolic representation of the sky at the time of your birth. It contains glyphs representing each of the planets (plus the Sun and Moon) placed in a wheel with twelve sections, which are called houses. The lines separating the houses are called house cusps.

So far, so good. Look up into the sky and you can see the Sun, Moon, and most of the planets an astrologer uses in your birth chart. But do you see any little lines, separating the sky into 12 pie slices, or “houses” like the ones you see on a birth chart? Hopefully not. If you do, fine-tune your reception.

It’s helpful, though, this concept of interpreting a planet based on its place in the sky at a particular moment, and which planet has dominion over a piece of the sky. So astrologers use a variety of “house systems,” or methods of dividing up the sky into twelve sections. How this is done is a critical question, because the method of splitting up the houses can determine the house placement of the planets. Each house has a particular vibe, focus, and landscape. For instance, in once house system you might find your Moon in the 8th house – a soulful, mysterious, sometimes brooding placement – while in another it appears in the more optimistic and gregarious 9th house. How can both be true?

If you ever find yourself among a group of astrologers and the conversation lags, introduce the subject of house systems and watch the fur fly! A lot of us have strong opinions about which is the best and why. What follows is a brief (believe it or not) summary of house systems – the ones that are popular, how they’re different, and why you should care.

Should you care about house systems?

‘m going to level with you: If you are a casual astrology hobbyist, the answer is probably “no.” (Also, if you don’t have an accurate birth time, the whole question of houses is moot – because the most popular house systems are derived from the Ascendant point, which changes about every four minutes. If your birth time is unknown, the Ascendant, and therefore the houses, can’t be accurately calculated. In that case, just use Solar or Whole Sign Houses at sunrise.)

But if your birth chart has planets that fall close to a house cusp, the question of house system becomes more pressing. If you’ve calculated your birth chart at Astro.com and are used to seeing your Venus in the festive 5th house and then someone else’s chart for you – calculated in a different system – places it in the more home-loving 4th house, you may feel disappointed. I’ll be honest: In cases like these, one often chooses the house system that gives them the chart they like best. For instance, my Placidus chart has Venus in the 7th house, but I simply relate better to my Koch chart’s 8th house Venus. I’m not saying this is the best approach to this dilemma, but it’s probably the most human.

If you were born above 66 N latitude or below 66 S latitude, your chart will “break” certain house systems. Either all the planets will fall in just a couple of houses, or the computer will default to an equal house system. I’m not going to go into why. But if you were born outside 66N and 66 S latitudes, consider just using Whole Sign houses or Equal Houses.

House systems in action

good explanation of different house systems and their theoretical and mathematical underpinnings can be found here. For many astrologers, though, house systems tend to be a matter of habit. Often, we pick one up from our teachers or the current popular trends and just stick with it, more or less unquestioningly.

For instance, my default house system since 1989 has been the Koch (pronounced “coke”) house system. If you run across an astrologer who uses Koch, it’s a good bet they came of astrological age in the late 1980s, when this system was all the rage and considered a bit more “technical” than the popular Placidus (pronounced “PLA-si-dus” – pla rhymes with “at”) system. Alternately, twenty years from now it will probably be another house system that’s in vogue, and all the early 21st century astrologers will be recognized by their use of Whole Sign houses.

Popular Systems and How They’re Different

Equal Houses Some house systems split the wheel into 12 equal sections of 30 degrees. Plus side: Elegantly simple, and no intercepted signs. Down side: Midheaven degree (normally the cusp of the 10th house) can move around to different houses, which can be disconcerting.

Whole Sign houses begins the first house cusp with 0 degrees of the Ascendant sign, the second house cusp with 0 degrees of the following sign, and so on. It’s the go-to system for Hellenistic astrologers and currently very popular, especially among younger astrologers. It ensures consistent planetary rulership of the houses (no pesky interceptions), which is particularly critical in certain forms of predictive astrology, such as horary or electional.

The Equal House system is similar, except it takes the degree and sign of the Ascendant and uses that degree of the next sign on the 2nd house cusp, and so forth. So if 12 degrees and 37 minutes of Leo are rising, the next house as 12.37 Virgo, the next 12.37 Libra, and so on. This system accentuates the importance of the Ascendant, which is arguably the most personal house cusp. It’s a bit of an “all about me” chart. If you don’t have an accurate birth time, you can use Solar Houses, which is basically equal houses with the Sun’s degree at sunrise on each of the house cusps.

Unequal houses

n these systems, houses usually vary in size, sometimes dramatically. Therefore, planets can fall in different houses depending on what house system is used to calculate your chart. These systems can also result in intercepted signs. For instance, you may have the same sign on two houses in a row, then skip a sign. The sign didn’t go away – all 30 degrees of it are in a house – but it doesn’t show up on a house cusp. It has to get its work done more subtly, behind the scenes, or through its planetary ruler. More about intercepted signs here.

The most popular of these systems are based in time – the time it takes for planets to move from the eastern horizon to the meridian, and from the meridian to the western horizon. They just vary in how they split up that time into house cusps. All agree on the Ascendant/Descendant degree and signs, and on the Midheaven/IC degree and signs. But the second/eighth, third/ninth, fifth/eleventh, and sixth/twelfth houses can be different from one system to the next.

Placidus is probably the most popular of these systems. If you’ve ever calculated your chart at Astro.com and didn’t change the default house system, you’re using a Placidus chart. Placidus is an elegant system with a lot of inherent wisdom, so don’t roll your eyes at it because it seems old-fashioned. It’s a very old house system and very respectable its house cusps correlate to the planetary hours, if you’re into that. If you want a nice, solid, pinstripes and sweater set type of house system, this one is for you. It’s a mess at extreme latitudes, though.

Koch will usually yield a very similar chart as one calculated in Placidus. Koch is an extremely modern system, with the table of houses published in the early 1970s. It will usually give a chart that’s very similar to Placidus, but the math behind it is a bit more straightforward and uses the Midheaven as its initial reference point. For this reason, the Midheaven is particularly important in this chart you could consider playing around with it to see if it gives particular insights into career matters. Note that, in contrast to the same chart in Placidus (above), Jupiter is now in the 4th house and Saturn is in the 5th. Like Placidus, though, this one falls apart at extreme latitudes.

Porphyry (POR-fur-y) is older than dirt. The math is more complicated than whole signs or equal houses, but much simpler than Placidus. The intermediate house cusps are based on the number of degrees between the angles. For instance, an Ascendant of 12.37 Leo and IC of 6.03 Scorpio is a difference of 83 degrees and 26 minutes. Divide that by 3, and you get about 27 deg and 48 minutes per house.

(Notice the similarity to the Placidus chart. However, a difference of a few degrees on the house cusp – e.g., 10 on the 2nd house in Porphyry vs 6 on the 2nd house in Placidus – can make a huge different when you’re tracking slow-moving transits or progressions.)

Which is best?

ersonally, I’m agnostic on the subject of house systems. After keeping a spreadsheet for years that tracks transits to my house cusps in different systems, I’m still not prepared to come down on any house system as the decisive winner. Other than the angles (cusps of the 1st/7th and 4th/10th houses), which represent observable points in the daily path of the planets, house cusps are, to me, a bit like past lives: you can believe whatever you want about them and have a 50/50 chance of being right.

I think house systems are like lenses that a photographer might use on a camera. You can take a photo of the exact same subject and see it very differently, just by using a different lens. Same truth, different perspective.

So when an astrologer tells me they use their house system because “it works,” I believe them. I also believe other systems work, because I’ve seen different astrologers produce great accuracy with many house systems. And so, if a client has strong feelings on the subject and asks me to use a particular house system, I’m more than happy to use their lens.

It’s complicated

hate to disappoint any readers who were hoping I’d settle this house system matter once and for all. It’s complicated it has to do with the ways that we interpret a three-dimensional universe using a one-dimensional map. There’s math involved – and deep philosophical questions.

To anyone who is advanced enough in their study of astrology to ask about house systems, I always recommend that they experiment with as many as they like, and maintain a spirit of inquiry and flexibility about it. I’m not an especially flexible person by nature, but I think I’m from a generation that could afford to be a little more fluid and philosophical in our approach to things. Today, the world is harder. There’s a yearning for certainty. Returning to ancient methods and carefully defined rules and techniques perhaps reflects astrology’s evolving role as a stabilizing rudder in the world’s turbulent waves.

If you want to go with the flow and not think about this too much, just use Placidus. If you want to go with what’s currently most popular among astrologers, that would probably be Whole Signs. And if you want to use what I use because you like me, go with Koch – but by all means, have fun investigating other possibilities!


Watch the video: Moon - lunar month (May 2022).