Why Comet C/2020 F3 Neowise returns even it's orbit is near- parabolic?

Why Comet C/2020 F3 Neowise returns even it's orbit is near- parabolic?

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I have read in Wikipedia about Comet C/2020 F3 Neowise that it's orbit is near-parabolic. But in another section, it says that it is a non-periodic comet whlith orbital period ranging from 4500 years to 6800 years.

My doubt is how a comet returns back if it is in a parabolic orbit and why it is non-periodic?

Here is the Wikipedia link:

Supplementary answer:

"Near-parabolic" means almost or nearly parabolic, but not quite. Another term would be "highly elliptical". Technically speaking, no realistic orbit can really be exactly parabolic since that means eccentricity is exactly 1.00000000000… and most of Physics (solar photon pressure, relativity, gravitational perturbations from other bodies, etc.) doesn't happen.

You can complain that in your linked Wikipedia article:

C/2020 F3 (NEOWISE) or Comet NEOWISE is a retrograde comet with a near-parabolic orbit discovered on March 27, 2020, by astronomers using the NEOWISE space telescope.

the term "near-parabolic" hyperlinks to Parabolic trajectory. Probably the "near" part should not be part of the link.

Comet naming conventions limit "periodic comets" to those comets whose orbital period is less than 200 years. Comets in elliptical orbits with a period of greater than 200 years are classified as non-periodic. Comets in parabolic or hyperbolic trajectories are also classified as non-periodic (and they will never again approach the primary).

Check Out These Breathtaking Pictures of NEOWISE Before the Comet Leaves Our Solar System for 6,800 Years

The comet NEOWISE&mdashfull name C/2020 F3 (NEOWISE)&mdashwas discovered on March 27 by astronomers analyzing data from the comet's namesake, the Near-Earth Object Wide-field Infrared Survey Explorer mission.

The WISE infrared space telescope, launched in 2009, began a re-activated survey of the sky in 2013 under its new name, NEOWISE, which appended "Near-Earth Object" to the original acronym. The name change highlighted its mission identifying and tracking comets and asteroids&mdashincluding Potentially Hazard Asteroids, or PHAs, projected to intersect Earth's orbit and get closer than 4.6 million miles to us.

In its first four years, NEOWISE collected approximately 10.3 million image sets, creating a database of more than 76 billion source detections. As of January 2019, NEOWISE had detected 158,000 asteroids, 34,000 of them new (and 135 of those newly discovered classified as near-Earth objects).

Operated by NASA's Jet Propulsion Laboratory in Pasadena, California, NEOWISE has discovered, as of June 2020, 33 comets and 313 asteroids classified as near Earth, with 57 of those considered potentially hazardous.

The discovery of C/2020 F3 (NEOWISE) has been one of the space telescope's most dramatic, since it captured a previously unknown asteroid on a close approach trajectory with Earth, which brought it as close as 64 million miles away from our planet, or about seven-tenths of the distance between Earth and the Sun. NEOWISE picked up on the comet that would take its name when it was approximately 160 million miles from Earth.

Here is a composite of the first images of the comet NEOWISE, taken on the day of its discovery. Processed from heat-sensitive infrared images, the red color of the comet indicates how much cooler it is than the background stars and galaxies.

Since then, it has become visible to the naked eye and is one of the brightest comets to be visible to Earth this century. Subsequent to observations made by NEOWISE, other NASA spacecraft have also spotted the comet, including the Parker Solar Probe, the Solar and and Terrestrial Relations Observatory (designed to take stereoscopic photos of the Sun), and the joint European Space Agency and NASA Solar and Heliospheric Observatory satellite, launched in 1995.

C/2020 F3 (NEOWISE) has also been seen and photographed by astronauts aboard the International Space Station.

The ISS currently has five people onboard. The members of Expedition 63 include NASA astronauts Chris Cassidy, Douglas Hurley, Robert Behnken, and Roscosmos cosmonauts Anatoly Ivanishin and Ivan Vagner.

Photographers and amateur astronomers from around the world have also been taking pictures of the comet. Here are 16 more breathtaking images of the comet C/2020 F3 (NEOWISE) taken from around the world, begining with this time-lapse of comet NEOWISE rising over the Adriatic Sea off the coast of Italy, taken by Paolo Girotti:

How to see NEOWISE, the best and brightest naked-eye comet in years

For the first time in many years, a bright naked-eye comet is gracing our skies: C/2020 F3 (NEOWISE). It's been up pre-sunrise for the past few weeks, but starting this week it starts to peek above the horizon after sunset, making it much easier on most people to see it. Over the next two weeks or so it'll be moving higher in the sky, and well placed for observing in the northern hemisphere.

It's difficult to predict how bright it will be, even over the coming few days. Comets are fickle! Until just a few days ago no one was sure if this one would even survive perihelion, its closest passage to the Sun — that occurred on 3 July, when it was 44 million kilometers from our star, about the same distance as Mercury from the Sun. Many small comets break up under the stress, but NEOWISE seems to have done very well, holding itself together and forming a very long tail that gives comets their iconic look (more on that in a sec).

Comet C/2020 F3 (NEOWISE) over St. Peter’s dome in Rome on 10 July 2020. Credit: Gianluca Masi/The Virtual Telescope Project

Right now its orbit is taking it closer to Earth, and on 23 July it'll be at perigee (closest to Earth) at a distance of just about 100 million km (so if you read any breathless doomsday articles saying it'll hit us, then 1) don't fret, and b) stop reading garbage like that). It probably won't get much brighter as it gets closer — it shines by reflected sunlight, so as it recedes from the Sun it gets dimmer due to less illumination, but that's offset by it getting closer to Earth — but it's still bright enough to be worth going out to see.

The comet C/2020 F3 NEOWISE rising over the village Spicheren, France on 07 July, 2020. Credit: Dr. Sebastian Voltmer

A dark site is best, but it should be visible even in somewhat light-polluted skies. Using binoculars is your best bet to get the best view, too. A telescope is great if you have one, and that'll show you details on the comet's head but does make it hard to get a good overview.

A map of the location of comet C/2020 F3 (NEOWISE) in the sky through the end of July 2020. Dubhe, Merak, and Phecda mark three points on the bowl of the Big Dipper. Credit: Cometwatch

Face northwest after sunset and it'll be low over the horizon, getting higher each evening. During the week of perigee, say, the 20th on, it will be below the bowl of the Big Dipper, so if you can find that the comet should be easy. Because it's low to the horizon, make sure the view is clear — no mountains, trees, buildings, and so on.

After about the 25th or so the Moon's light will start to be a problem as it waxes (gets more full), so get out as soon as possible to look. Also, after perigee it'll likely fade rapidly as it recedes from Earth.

Comet C/2020 F3 (NEOWISE) from before sunrise on 8 July 2020, taken using a 30-cm telescope in British Columbia. The multiple “hoods” around it may be from jets blowing out dust from the comet’s surface, created as the comet nucleus spins. Credit: Debra Ceravolo

It won't look like the photos you see here or elsewhere online — cameras take long exposures, and see fainter details. That's why binoculars are so helpful. But seeing a comet with your own eyes is something special. I've seen quite a few and it never gets old. Never.

So if you see it, what exactly are you seeing?

Comets are icy-rocky bodies, usually a few kilometers in size (this solid part is called the nucleus). They come in a lot of varieties, but some are on extremely elongated orbits that take them from way out in the outer solar system down toward the Sun. As they warm up the ice in them sublimates, turning from a solid into a gas. This dislodges a lot of fine-grained dust, which gets gently blown back by the pressure of sunlight, forming the long dust tail. We see it by reflected sunlight, so it looks yellowish. It curves because the force on the dust grains is small, so they mostly follow the comet along on its orbit, moving away from it slowly.

At the same time, ultraviolet light from the Sun zaps the atoms and molecules in the gas, ionizing them (stripping them of one or more electrons). This allows the solar wind — a stream of subatomic particles from the Sun — to drag the gas away via its magnetic field, creating the ion tail. Because the solar wind is fast (400 km/sec in many cases) the ion tail points directly away from the Sun. This is usually blue from ionized carbon monoxide (CO+), or green from diatomic carbon (C2), both of which are common in comets. Changes in the solar wind magnetic field can cause ripples in the ion tail, too.

A spectacular shot of C/2020 F3 (NEOWISE) shows its magnificent yellow dust tail, its blue ion tail, and an unusual red ion tail. Credit: Bray Falls

NEOWISE appears to have two ion tails, one blue as usual, and the other red. I haven't seen anything definitive on what this might be from — sulfur ions glow red, but that seems unlikely to me in a comet, and while sodium is more common it tends to glow yellow — but if I hear anything I'll update this post.

A spectacular real-time video of comet C/2020 F3 (NEOWISE) rising over the limb of the Earth as seen by astronauts on the International Space Station. Credit: NASA / Seán Doran

The orbit of the comet is interesting. Its original orbit took it out as far as 81 billion kilometers, well out into the Kuiper Belt beyond Neptune, and it took roughly 4500 years to orbit the Sun once. However, the gravitational effects of the planets changed the orbit somewhat, elongating it. Now it will get about 100 billion km from the Sun on a 6800 year orbit. So see it while you can it won't be back until the 89th century.

A composite of the three discovery images of comet C/2020 F3 (NEOWISE) taken from NASA’s NEOWISE spacecraft. The comet’s motion (red) makes it stand out from background stars. Credit: NASA/JPL-Caltech

It was discovered by the NEOWISE spacecraft (hence the comet's name). Originally the mission was called WISE: Wide-field Infrared Survey Explorer, which mapped the entire sky in infrared. The frozen hydrogen it used for coolant ran out after about a year, which limited what colors of infrared it could see. The mission was then recast as the Near-Earth Object WISE mission, to look for asteroids. Observations of the comet by NEOWISE were used to find that the comet's solid nucleus is about 5 kilometers across, so it's decently big, explaining why it survived being close to the Sun and also why it's so bright.

One of the more unusual images of comet NEOWISE comes from NASA’s Parker Solar Probe, in orbit around the Sun, so it sees the comet from a different angle. This is from 5 July, and clearly sees details in both the broad dust tail and the sharper ion tail(s). Credit: NASA/Johns Hopkins APL/Naval Research Lab/Parker Solar Probe/Guillermo Stenborg

If you can't get to see the comet, or have cloudy skies, then the Virtual Telescope Project is holding a live viewing on the 23rd. I also have a list of astrophotographers I follow on Twitter, and they will no doubt be posting amazing photos of NEOWISE in the coming days and weeks as well. Sky and Telescope has some great shots, too, and honestly it's so bright and easy to spot that just typing the comet's name in your favorite search engine will yield a gazillion gorgeous photos of it.

The Best Way to Watch Comet NEOWISE, Wherever You Are

Comet NEOWISE has been entertaining space enthusiasts across the Northern Hemisphere. Although its official name is C/2020 F3, the comet has been dubbed NEOWISE after the Near-Earth Object Wide-Field Infrared Survey Explorer (NEOWISE) space telescope that first noticed it earlier this year. This &ldquoicy snowball&rdquo with a gassy tail made its closest approach to the sun on July 3 and is now heading back from whence it came: the far reaches of the outer solar system. Its long, looping orbit around our star ensures that after passing closest to Earth on July 22, Comet NEOWISE will not return for some 6,800 years.

Even though the comet is now bright enough to observe with unaided eyes, inexperienced stargazers might have trouble knowing when and where to look. Scientific American spoke to Jackie Faherty, an astronomer at the American Museum of Natural History in New York City, for observing tips and a better appreciation of why comets are so special.

[An edited transcript of the interview follows.]

How does one prepare to watch Comet NEOWISE with the naked eye?

Find the darkest possible swath of sky and make sure your eyes are adjusted so that you give yourself the best possible opportunity to see faint objects. It means: don&rsquot just walk outside after staring at lights or screens and expect to see [the comet] really well. You need 15 minutes or so to adjust your eyes, so that your pupils are adjusted, and they&rsquore used to seeing fainter things. It&rsquos the same as walking into a dark room, and everybody knows that [you] can&rsquot see [things] first&mdashand then, all of a sudden, you start seeing things. You need to do the same thing when you walk outside. And use the Comet NEOWISE app developed by astrophysicist Hanno Rein of University of Toronto Scarborough to see exactly where it is, so that you know what direction you need to look. And then the key would be to find yourself a place that is the darkest possible, that [has] no lights.

Which direction should one look?

[The comet] appears [in the evening] in the northwestern sky. But the easiest thing is [to use] the app to help you [find it].

When is the best time to watch?

We&rsquore going to catch [the comet] in the evening sky. We&rsquore calling it primetime viewing, which is when the sun has just set.

Comet NEOWISE above Hollywood. Credit: Zihao Chen Getty Images

Will Comet NEOWISE be brightest when it&rsquos closest to us?

Well, it&rsquos a trade-off. When [the object is] closer to the sun, it&rsquos getting heated up. And so it&rsquos brighter because it&rsquos outgassing [warming so that its ice turns to vapor], and it&rsquos got the light reflecting off of [the gas]. [But] you couldn&rsquot really see it [earlier], when it was in the glare of the sun.

And when it&rsquos closer to us, it gets brighter, because of [the decrease in] distance. Something that&rsquos closer to you is going to be easier to see, even if it&rsquos fainter.

Would we be able to see the comet in megacities such as New York and Los Angeles?

I have seen shots [from] residential areas in L.A. And I can&rsquot believe that people saw the thing through the light pollution in L.A., which I would have thought would be worse than [in] New York City.

What I often advise people during meteor showers, which are similar in some ways, is to go to rooftops. A rooftop can give you a very clear view to the horizon, and it&rsquoll let you get away from light pollution.

Upper Manhattan&rsquos Inwood Hill Park is always an excellent spot for low light pollution in [New York City], or toward the piers on the West Side. New Jersey is not so bad with light pollution when you&rsquore looking in that [northwestern] direction. The Intrepid Sea, Air & Space Museum used to have an excellent spot for stargazing on [its] platform. And amateur astronomers used to go to the High Line [in the neighborhood of Chelsea]&mdashthat&rsquos a nice darkish area.

Does it matter where in the U.S. you&rsquore located?

[Your location] will change how high above the horizon [the comet] gets for you. But because this is Northern Hemisphere&ndashaccessible, the U.S. has a visibility window that&rsquos excellent for the country. I&rsquove seen the shots from New York to California to Florida.

Would someone be able to take a good picture using a smartphone?

Your best [bet is] to have [a smartphone&rsquos camera] on a longer exposure. The longer the exposure, the better the picture, because [the comet] is faint, and you will see it as this fuzzy thing. Your eye can&rsquot quite do that for you. You make your eye open, but it can't record the photons and let them accumulate, and that&rsquos what the camera is able to do.

What is the comet going to do next?

[After] July 22, it gets dimmer and dimmer as it gets farther from Earth. And it very quickly becomes something that you cannot see with your naked eye, even on the clearest night. But [with] binoculars or a telescope, we&rsquoll still be good for seeing it for a while. Then it goes off to the outer part of the solar system, and it&rsquoll be gone for a couple thousand years before it makes the trip back. It has a long orbit around the sun most comets do. It takes them hundreds or thousands of years in order to go around the sun. They [mostly] hang out in the outer part of the solar system.

Why should anyone care about comets?

If you could capture the comet and bring it back down to Earth and study it in a lab, you would have one of the holy grails for understanding the ingredients to make a planet&mdashand possibly to make it habitable. Like, &ldquoHow did life get delivered here?&rdquo Comets are one of the things we look to for answers. They&rsquove got all that primordial material that was around to form the planet that would become Earth&mdashbeing filled with water and have life teeming on it. So from that perspective, a comet is a really important object to study. But we can&rsquot capture it and bring it back down here.

We&rsquove attempted to land on a comet before. We did this with Comet 67P. It was a European mission, and the whole thing was called Rosetta, with this Philae lander. [Now] we have a really cool mission called OSIRIS-REx. And this is a mission to an asteroid called Bennu that is going to land, acquire a sample and return it to Earth, which is awesome and crazy.

Comets were often markers&mdashomens&mdashbefore we understood what they were. That&rsquos how people saw them&mdashthe bearers of good things, the bearers of bad things. I find it fascinating that in this year 2020 we have a marker in the sky. And it&rsquos a reminder that we should look up more. We should pay attention to the sky [and what] it brings us.

Comet NEOWISE over Stonehenge. Credit: Getty Images

Can anyone predict when the next bright comet will come?

Can we predict the next naked-eye-exciting comet, the one that&rsquos going to come in and wow us all the way that NEOWISE is wowing us right now? There are some that are lining up that will make a good appearance&mdashsuch as Halley&rsquos Comet, for instance. That orbit is like 80 years or something. So we know when [that comet is] coming we know when it&rsquos going. But [what] you want to know is: &ldquoIs there going to be one next year? Is there going to be one next month?&rdquo Unfortunately, comets are just unpredictable, erratic beasts. You don&rsquot know what&rsquos going to happen to them as they get close to the sun. Sometimes they just break apart. Comets are notoriously unpredictable. So I can't tell you the next one.

The NEOWISE space telescope is monitoring the sky, looking for these kinds of things. And there are several different surveys that are on the lookout for objects that are going to come close to Earth. But who knows when they will find them. That is the beauty of science: scientists are looking at the data every day and trying to find something.

Moon muscles in

Since rounding the sun, the comet has slowly been getting higher in the northwest evening sky and its position relative to the Big Dipper has made it fairly easy to find. But now, an object that has been all but absent from the evening sky since NEOWISE rounded the sun, is now back in view and will pose an increasing hindrance to comet watchers with each passing night.

This weekend it will be a widening crescent and its light will not pose too much of a nuisance, but on Monday (July 27) it will reach its first quarter ("half") phase, and in the nights thereafter it will be a waxing gibbous, and flooding the late night and early morning sky with its light during the coming week. And now that the comet is now moving away from both the sun and the Earth, it will continue to fade though at a more rapid pace.

According to the most recent predictions by the Central Bureau for Astronomical Telegrams, NEOWISE will likely drop below fifth magnitude by the end of July and that, combined with the light of an almost full moon will mean that almost certainly it will no longer be visible without binoculars or a small telescope.

So, this final weekend of July will probably afford most with their last chance to get a really good look at this visitor from far beyond the outer limits of our solar system. The comet's proximity to the Big Dipper will greatly assist locating it. Just remember that your clenched fist held at arm's length measures roughly 10 degrees. On Saturday and Sunday nights (July 25-26), about two hours after sunset, face northwest to find the Big Dipper.

Go approximately 15 degrees (about "one and half fists") down and to the lower left of the bottom of the "bowl" of the Big Dipper, and ultimately you will arrive in the vicinity of the comet. If you're located in a dark location, free of bright lights, you should be able to make out the comet as a pale streak of light with your naked eye.

Another tip: when looking at the comet, have your eyes slightly averted in order to see it best. Because of the structure of the eye, faint objects are seen more clearly when not looked at directly. Two hours after sunset, NEOWISE will stand more than 20 degrees ("two fists") above the west-northwest horizon.

If you still can't see it, that's where binoculars will be most beneficial binoculars (or a low-power telescope) will certainly enhance the view because of their greater light-gathering power.

The comet is traveling at about 40 miles per second (that's about 144,000 mph, or 231,000 km/h).

Joe Masiero, deputy principal investigator of the NEOWISE mission, said the the comet is moving about twice as fast as the Earth's speed around the sun. But don't expect that rapid clip to last.

Because of the comet's extremely elliptical orbit, it will slow down as it reaches its farthest point from the sun, then fall back toward the inner solar system and accelerate again when it heads back round the sun. That trip around the sun is over for Comet NEOWISE's current orbit and it's moving back to the outer solar system.

"And so as it goes farther from the sun, [it] will be slowing down as it climbs back up that gravity well," Masiero said.

Comet streaking past Earth, providing spectacular show

Comet Neowise soars in the horizon of the early morning sky in this view from the near the grand view lookout at the Colorado National Monument west of Grand Junction, Colo., Thursday, July 9, 2020. The newly discovered comet is streaking past Earth, providing a celestial nighttime show after buzzing the sun and expanding its tail. (Conrad Earnest via AP)

A newly discovered comet is streaking past Earth, providing a stunning nighttime show after buzzing the sun and expanding its tail.

Comet Neowise—the brightest comet visible from the Northern Hemisphere in a quarter-century—swept within Mercury's orbit a week ago. Its close proximity to the sun caused dust and gas to burn off its surface and create an even bigger debris tail. Now the comet is headed our way, with closest approach in two weeks.

NASA's Neowise infrared space telescope discovered the comet in March.

Scientists involved in the mission said the comet is about 3 miles (5 kilometers) across. Its nucleus is covered with sooty material dating back to the origin of our solar system 4.6 billion years ago.

The comet will be visible across the Northern Hemisphere until mid-August, when it heads back toward the outer solar system. While it's visible with the naked eye in dark skies with little or no light pollution, binoculars are needed to see the long tail, according to NASA.

It will be about 7,000 years before the comet returns, "so I wouldn't suggest waiting for the next pass," said the telescope's deputy principal investigator Joe Masiero of NASA's Jet Propulsion Laboratory in Pasadena, California.

  • In this image released by NASA, Comet Neowise, left, is seen in the eastern horizon above Earth in this image taken from the International Space Station on Sunday, July 5, 2020. (NASA via AP)
  • Comet Neowise soars in the horizon of the early morning sky in this view from the near the grand view lookout at the Colorado National Monument west of Grand Junction, Colo., Thursday, July 9, 2020. The newly discovered comet is streaking past Earth, providing a celestial nighttime show after buzzing the sun and expanding its tail. (Conrad Earnest via AP)
  • The Comet NEOWISE or C/2020 F3 is seen above Salgotarjan, Hungary, early Friday, July 10, 2020. It passed closest to the Sun on July 3 and its closest approach to the Earth will occur on July 23. (Peter Komka/MTI via AP)
  • The Comet NEOWISE or C/2020 F3 is seen above Cered, Hungary, Monday, July 6, 2020. It passed closest to the Sun on 03 July and its closest approach to Earth will occur on 23 July. (Peter Komka/MTI via AP)
  • The Comet NEOWISE or C/2020 F3 is seen above Salgotarjan, Hungary, early Friday, July 10, 2020. It passed closest to the Sun on July 3 and its closest approach to the Earth will occur on July 23. (Peter Komka/MTI via AP)
  • The Comet NEOWISE or C/2020 F3 is seen above Cered, Hungary, Monday, July 6, 2020. It passed closest to the Sun on 03 July and its closest approach to Earth will occur on 23 July. (Peter Komka/MTI via AP)

He said it is the brightest comet since the mid-1990s for stargazers in the Northern Hemisphere.

Astronauts aboard the International Space Station have already caught a glimpse.

NASA's Bob Behnken shared a spectacular photo of the comet on social media late Thursday, showing central Asia in the background and the space station in the foreground.

"Stars, cities, spaceships, and a comet!" he tweeted from orbit.

© 2020 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed without permission.

New comet NEOWISE graces the skies

Comet NEOWISE captured on July 6, 2020 above the northeast horizon just before sunrise in Tucson. Viewers in the region can find the comet in the northeastern sky near the horizon between 4 and 4:30 a.m. until July 11, after which it will be visible in the northwestern sky just after sunset, below the Big Dipper. Credit: Vishnu Reddy

A comet visiting from the most distant parts of our solar system is putting on a spectacular nighttime display. The comet C/2020 F3 NEOWISE made its once-in-a-lifetime close approach to the sun on July 3 and will cross outside the Earth's orbit on its way back to the outer parts of the solar system by mid-August.

"For the next couple of days, Arizona viewers can catch a glimpse of the comet in the early morning northeastern sky near the horizon between 4 and 4:30 a.m.," said Amy Mainzer, a University of Arizona professor of planetary sciences. "Then, on July 11, it will begin to be visible in northwestern sky just after sunset, just below the constellation Ursa Major," which contains the Big Dipper.

Mainzer is the principal investigator of NASA's Near-Earth Object Wide-field Infrared Survey Explorer, or NEOWISE, mission, which discovered the comet on March 27.

Its very close passage by the sun is cooking the comet's outermost layers of gas and dust and lofting them into a large, wide tail of debris, yet the comet has managed to survive this intense roasting. Observers all over the world—and off it—are racing to capture this natural firework display before the comet speeds away into the blackness of space. Even the astronauts aboard the International Space Station spotted it from their vantage point high above Earth's surface.

Observers might be able to see the comet's central core, or nucleus, with the naked eye in dark skies using binoculars will give viewers a good look at the fuzzy comet and its long, streaky tail, which looks a bit like the beam of a flashlight pointing up.

NEOWISE spotted the icy visitor using its two infrared channels that are sensitive to heat signatures given off by the object baking in the sunlight.

Comet NEOWISE appears as a string of fuzzy red dots crossing through the constellation Puppis in this composite image that combines multiple exposures taken by the NEOWISE mission on March 27. The comet appears red in this heat-sensitive infrared image because it is much cooler than the background stars, which are thousands of degrees. Credit: University of Arizona/NASA/Jet Propulsion Laboratory

The NEOWISE spacecraft—originally named the Wide-Field Infrared Survey Explorer, or WISE—launched in December 2009. WISE was not designed to study asteroids and comets and is now long past its expected lifetime of seven months. Although incapable of discovering large numbers of near-Earth asteroids and comets, the spacecraft has provided information on asteroid and comet numbers and sizes based on a small sample of them. NEOWISE was repurposed for this use in 2013 by what is now known as NASA's Planetary Defense Coordination Office.

"In its discovery images, comet NEOWISE appeared as a glowing, fuzzy dot moving across the sky even when it was still pretty far away. As soon as we saw how close it would come to the sun, crossing inside the orbit of Mercury, we had hopes that it would put on a good show," Mainzer said.

The search for asteroids or comets that could potentially impact Earth also expands scientific understanding of primitive solar system bodies like comets. In this case, comet NEOWISE will pass harmlessly at 64 million miles from Earth while giving astronomers the opportunity to learn more about its composition and structure.

"From its infrared signature, we can tell that it's about 5 kilometers, or 3 miles, across, and by combining the infrared data with visible light images, we can tell that the comet's nucleus is covered with sooty, dark particles leftover from its formation near the birth of our solar system 4.6 billion years ago," said NEOWISE Deputy Principal Investigator Joseph Masiero from NASA's Jet Propulsion Laboratory.

The NEOWISE mission is not expected to last much longer due to the nature of its orbit and will eventually harmlessly re-enter Earth's atmosphere. The University of Arizona and the Jet Propulsion Laboratory are working on the formulation of a highly capable next-generation space-based telescopic survey—the Near-Earth Object Surveillance Mission, or NEOSM.

C/2020 F3 (NEOWISE)

C/2020 F3 (NEOWISE), or Comet NEOWISE is a newly-discovered comet. It was discovered on March 27, 2020, by the NEOWISE space telescope (a NASA infrared-wavelength astronomical space telescope launched in December 2009 and placed in hibernation mode in February 2011 and re-activated in 2013). It is a retrograde comet with a near-parabolic orbit. It passed closest to the Sun on July 3, 2020.

In astronomy, retrograde motion is in astronomy is an orbital or rotational motion of an object in the direction opposite the rotation of its primary (in this instance, the Sun).

Comet NEOWISE had an orbital period of about 4800 years. But, its last perihelion passage (nearest point to the Sun, which was 0.29 AU or 43 million km or 26.7 million miles an occurred in June 2020) will increase it to about 6800 years.

What is a comet?

Like asteroids, comets are space rocks too. They were formed around the same time as asteroids and they are leftovers from the formation of our solar system too. However, the biggest difference between an asteroid and a comet is what they are made of. Comets are icy bodies, unlike the rocky asteroids. Because they formed at farther distances from the Sun than the asteroids.

Asteroids formed toward the inner regions of our solar system where temperatures were hotter. As a result, only rock or metal could remain solid without melting. temperatures were hotter and thus only rock or metal could remain solid without melting. Comets have a solid, core structure which is known as the nucleus composed of an amalgamation of rock, dust, water ice, and frozen carbon dioxide, carbon monoxide, methane, and ammonia. That’s why they are popularly described as “dirty snowballs”.

Comets also have an extended, gravitationally unbound atmosphere surrounding their central nucleus. This atmosphere has parts termed the coma (the central part immediately surrounding the nucleus) and the tail (a typically linear section consisting of dust or gas blown out from the coma by the Sun’s light pressure or outstreaming solar wind plasma). However, extinct comets that have passed close to the Sun many times have lost nearly all of their volatile ices and dust and may come to resemble small asteroids.

ALPO Comet News for June 2021

The monthly Association of Lunar and Planetary Observers (ALPO) Comet News PDF can be found on the ALPO Comets Section website @ http://www.alpo-astr. org/cometblog/. A shorter version of this report is posted here (minus magnitude estimates and figures). The ALPO Comet Section welcomes all comet related observations, whether textual descriptions, images, drawings, magnitude estimates, or spectra. You do not have to be a member of ALPO to submit material, though membership is encouraged. To learn more about the ALPO, please visit us @ We can also be reached at < comets @ >.

Comets C/2020 T2 (Palomar) and 7P/Pons-Winnecke should vie for the title of brightest comet of June though they should only reach magnitude 10.0. While June won’t see any “bright” comets, there are a large number of fainter objects, in addition to the aforementioned comets, between magnitudes 10 and 13. These fainter objects include some low numbered periodic comets (4P/Faye, 8P/Tuttle, 10P/Tempel, and 15P/Finlay) and long period comets C/2019 L3 (ATLAS), C/2020 J1 (SONEAR), and C/2020 R4 (ATLAS). C/2021 A1 (Leonard) is still inbound and has the potential to be a notable object at the end of the year, though its lack of recent brightening is concerning.

During the month of May 2021, the ALPO Comets Section received 32 images and/or sketches from Denis Buczynski, John Chumack, Carl Hergenrother, Martin, Mobberley, Mike Olason, Gregg Ruppel, John D. Sabia, and Chris Schur of the following comets: 4P/Faye, 6P/d’Arrest, 7P/Pons-Winnecke, 8P/Tuttle, 10P/Tempel, 15P/Fnlay, 17P/Holmes, 28P/Neujmin, 57P/du Toit-Neujmin-Delporte, 67P/Churyumov-Gerasimenko, 117P/Helin-Roman-Alu, C/2017 K2 (PANSTARRS), C/2019 K7 (Smith), C/2020 H5 (Robinson), C/2020 S1 (SONEAR), C/2020 R4 (ATLAS), C/2020 S3 (Erasmus), C/2020 T2 (Palomar), C/2021 A1 (Leonard), C/2021 A9 (PANSTARRS), and C/2021 E3 (ZTF).

On the magnitude front, J. J. Gonzalez, Carl Hergenrother, and Chris Wyatt submitted 43 visual and CCD/CMOS brightness measurements of comets 7P/Pons-Winnecke, 117P/Helin-Roman-Alu, 246P/NEAT, C/2017 K2 (PANSTARRS), C/2018 U1 (Lemon), C/2019 F1 (ATLAS-Africano), C/2019 T4 (ATLAS), C/2020 F5 (MASTER), C/2020 J1 (SONEAR), C/2020 R4 (ATLAS), C/2020 T2 (Palomar), and C/2021 A1 (Leonard).

The Comets Section Image Gallery (http://www.alpo-astr. nd-Observations) also reached a milestone in May when the number of images/sketches passed the 6000 mark. The next milestone is the total number of different comets represented in the Gallery. We are only 4 comets away from having images of 600 comets.

We plan on publishing our analysis of the bright comets of 2019 in an upcoming issue of the Journal of the ALPO. If you have any comet observations from 2019, especially for comets 260P/McNaught, C/2018 N2 (ASSASN), C/2018 W2 (Africano), and C/2018 Y1 (Iwamoto), please consider sending them to the Comets Section at < comets @ >. We would like to thank Jef De Wit, Uwe Pilz, and Michael Rosolina who recently contributed sketches of 2019’s brighter comets.

Bright Comets (magnitude < 10.0)

None, though there is a chance that C/2020 T2 (Palomar) and 7P/Pons-Winnecke may surprise us and become brighter than predicted. Those two comets are described in the following section.

Fainter Comets of Interest (generally between magnitude 10.0 and 13.0)

C/2020 T2 (Palomar) – While no comets are expected to be brighter than magnitude 10.0 this month, let’s kick off the “Fainter Comets of Interest” section with two comets that should come close to magnitude 10.0 and, with luck, could become brighter.

C/2020 T2 (Palomar) was discovered on 2020 October 7 at 19th magnitude and heliocentric distance of 4.4 au. The Zwicky Transient Facility (ZTF) used the 1.2-m Schmidt on Mount Palomar for the discovery. C/2020 T2 (Palomar) is a long-period comet with perihelion next month on July 11 at 2.05 au and an orbital period of

Visual observations by J. J. Gonzalez, Carl Hergenrother, and Chris Wyatt placed Palomar between magnitude 9.8 and 11.1 with a coma diameter between 3.5’ and 7’ in May. CCD observations by Carl Hergenrother on May 31 found the comet at magnitude 9.7 with a large 14’ coma. This bright and large coma was confirmed by other CCD measurement submitted to the COBS site. For example, Thomas Lehmann (ICQ code LEHaa) measured a magnitude of 10.1 and coma diameter of 17’ on May 19.90 UT.

June should see C/2020 T2 maintain a peak brightness between 10.0 and 10.5 as it moves through Boötes in the evening sky. Imagers should be on the lookout for any narrow dust tail/trail features as the Earth passes through Palomar’s orbital plane on June 14.

C/2020 T2 (Palomar)
T = 2021-Jul-11 q = 2.05 au Max El
Long-period comet –

5700-year orbital period (deg)
Date R.A. Decl. r d Elong Const Mag 40N 40S
2021-Jun-01 13 36 +23 09 2.110 1.443 117E Boo 10.4 72 27
2021-Jun-06 13 37 +21 08 2.097 1.460 114E Boo 10.4 69 29
2021-Jun-11 13 38 +19 02 2.086 1.479 112E Boo 10.4 64 31
2021-Jun-16 13 41 +16 50 2.077 1.502 109E Boo 10.4 60 33
2021-Jun-21 13 43 +14 36 2.069 1.529 107E Boo 10.4 56 36
2021-Jun-26 13 47 +12 20 2.063 1.558 104E Boo 10.4 51 38
2021-Jul-01 13 51 +10 02 2.058 1.591 102E Boo 10.4 47 40
2021-Jul-06 13 55 +07 44 2.056 1.626 99E Boo 10.4 43 42
Comet Magnitude Parameters --- H = 7.7, 2.5n = 8.0

7P/Pons-Winnecke – Comet Pons-Winnecke was discovered on 1819 June 12 by Jean-Luis Pons and independently re-discovered 39 years later on 1858 March 9 by Friedrich August Theodor Winnecke. Throughout the 19th and early 20th century, Pons-Winnecke routinely reached 6th magnitude during its better placed apparitions. In 1927 during an especially close approach to Earth (0.04 au), the comet peaked at magnitude 3.5. Unfortunately, it hasn’t had a bright return since 1939 (6th magnitude) and nowadays usually gets no brighter than

10-11th magnitude. The recent drought of bright 7P apparitions is due to an increase in perihelion distance from 0.76 au in 1841 to a maximum of 1.26 au in 1989. This year’s perihelion occurred on 2021 May 27 at 1.23 au.

Three visual observations were submitted to the ALPO Comets Section. J. J. Gonzalez observed a very diffuse 2.5’ coma at magnitude 11.3 on May 08.13 UT. 5 nights later (May 13.72 UT), Chris Wyatt reported a fainter comet at magnitude 14.4. He also saw a much smaller coma (0.3’) suggesting the fainter magnitude estimate was due to not detecting all of 7P’s coma. When Chris next observed the comet on May 19.62 UT, he saw a larger coma (2.0’) and made a brighter magnitude estimate at 12.8. He also reported the comet was easier to see in a Swan band filter which enhances gas emissions. CCD/CMOS photometry submitted to the COBS site found the comet to be as bright as magnitude 10.8 in mid-May with coma diameters as large as 10’.

7P has a history of outbursts. In 2008, a

3 magnitude outburst occurred a few months before perihelion. Just recently, Mike Kelley reported on comets-ml the detection of a

0.7 magnitude outburst which started sometime between May 30 and June 2. As a result of this recent outburst, imagers have been detecting some interesting inner coma structure.

Barring further outbursts, Pons-Winnecke should reach peak brightness in mid-June at magnitude 10.5. This is a few weeks after perihelion and around the time of closest approach to Earth on June 12 at 0.44 au. The comet also sees it peak brightness skewed a few weeks after perihelion. 7P is observable from both hemispheres as it traverses the morning constellations of Capricornus (Jun 1-7), Aquarius (7-20), Pisces Austrinus (20-27) and Sculptor (27-30).

Photo Op Alert:
June 14/15 with the Helix Nebula (NGC 7293 / Caldwell 63)

T = 2021-May-27 q = 1.23 au Max El
Jupiter-family comet - 6.31-yr orbital period (deg)
Date R.A. Decl. r d Elong Const Mag 40N 40S
2021-Jun-01 21 32 -11 25 1.236 0.452 108M Cap 10.9 29 62
2021-Jun-06 21 52 -14 49 1.240 0.445 110M Cap 10.8 26 65
2021-Jun-11 22 11 -18 19 1.248 0.442 111M Aqr 10.7 22 69
2021-Jun-16 22 30 -21 51 1.258 0.443 113M Aqr 10.6 19 72
2021-Jun-21 22 47 -25 20 1.272 0.448 114M PsA 10.6 17 76
2021-Jun-26 23 04 -28 43 1.288 0.456 116M PsA 10.5 14 79
2021-Jul-01 23 18 -31 54 1.307 0.467 118M Scl 10.6 12 82
2021-Jul-06 23 31 -34 55 1.328 0.482 120M Scl 10.6 10 85
Comet Magnitude Parameters --- H = 11.7, 2.5n = 12.5, offset = +50 days

4P/Faye – In March 1841, comet 4P/Faye passed within 0.64 au of Jupiter resulting in a decrease in perihelion distance from 1.80 to 1.69 au. Perhaps because of the smaller perihelion distance, the comet became bright enough to be discovered visually by Herve Faye on 1843 November 23 at 5th-6th magnitude. Or it is possible P/Faye experienced an outburst unrelated to the closer perihelion. Regardless, the discovery apparition proved to be anomalously bright. Most subsequent apparitions saw 4P max out at 9-10th magnitude at best. Since discovery, its perihelion distance has been stable ranging between 1.59 and 1.75 au.

This year marks the comet’s 22nd observed return and is a moderately good return with perihelion on September 8 at 1.62 au and closest approach to Earth on December 5 at 0.94 au. In June, Faye is a morning object brightening from around magnitude 13.7 to 12.5 as its moves through the morning constellations of Pisces (Jun 1-26) and Aries (26-30). Peak brightness should occur at the end of September near magnitude 10.3.

The nucleus of Comet Faye has been directly observed by the Hubble Space Telescope at multiple apparitions and was measured to be 3.5 km in diameter.

T = 2021-Sep-09 q = 1.62 au Max El
Jupiter-family comet - 7.48-yr orbital period (deg)
Date R.A. Decl. r d Elong Const Mag 40N 40S
2021-Jun-01 00 43 +07 57 1.905 2.247 57M Psc 13.7 11 31
2021-Jun-06 00 55 +08 59 1.880 2.186 59M Psc 13.5 12 31
2021-Jun-11 01 07 +10 00 1.856 2.126 60M Psc 13.3 14 32
2021-Jun-16 01 19 +11 00 1.833 2.068 62M Psc 13.1 16 32
2021-Jun-21 01 32 +11 58 1.811 2.010 63M Psc 12.9 18 32
2021-Jun-26 01 45 +12 53 1.790 1.954 65M Psc 12.7 20 32
2021-Jul-01 01 58 +13 47 1.769 1.900 66M Ari 12.5 23 32
2021-Jul-06 02 11 +14 37 1.750 1.846 68M Ari 12.3 25 31
Comet Magnitude Parameters --- H = 3.9, 2.5n = 28.9

8P/Tuttle – Similar to the discovery story of 7P/Pons-Winnecke, 8P/Tuttle was discovered during two widely separated apparitions. Pierre François André Méchain was the first discoverer in January 1790. Sixty-eight years later, 8P was re-discovered by Horace Parnell Tuttle in January 1858. With a 13.6-year period, 8P/Tuttle is making its 13th observed return having been missed in 1953 and at the 4 perihelion passages between the 1790 and 1858 discoveries. Tuttle’s relatively large semi-major axis of 5.7 au and inclination of 54.9° makes it a Halley-type rather than a Jupiter-family comet. It is also the parent body of December’s Ursid meteor shower.

This year perihelion will be on August 27 at 1.03 au with a closest approach to Earth on September 12 at 1.81 au. Currently, 8P is a very difficult object to observe being invisible to southern hemisphere observers in June and located at very low elevations for northern observers. It will reappear for southern hemisphere observers in late August at 9th magnitude as it brightens to 8.5 in September.

Tuttle’s best return was in 2008 when it passed 0.25 au from Earth and brightened to 5th magnitude. That close approach allowed radar observations to resolve its 10 km (6 mile) in diameter contact binary nucleus. Two returns from now in 2048, it will have an excellent return with a an Earth close approach distance of only 0.17 au.

T = 2021-Aug-27 q = 1.03 au Max El
Halley-family comet - 13.6-yr orbital period (deg)
Date R.A. Decl. r d Elong Const Mag 40N 40S
2021-Jun-01 03 28 +45 01 1.631 2.470 26 Per 14.5 9 0
2021-Jun-06 03 47 +44 32 1.580 2.428 26 Per 14.2 8 0
2021-Jun-11 04 07 +43 52 1.530 2.386 25 Per 13.9 7 0
2021-Jun-16 04 27 +43 00 1.481 2.344 24 Per 13.6 6 0
2021-Jun-21 04 46 +41 56 1.432 2.302 23 Per 13.3 6 0
2021-Jun-26 05 06 +40 39 1.385 2.261 23 Aur 13.0 5 0
2021-Jul-01 05 25 +39 08 1.339 2.220 22 Aur 12.7 4 0
2021-Jul-06 05 44 +37 24 1.295 2.180 22 Aur 12.4 3 0
Comet Magnitude Parameters --- H = 7.0, 2.5n = 20.0, offset = +25 days

10P/Tempel – 10P/Tempel’s 2021 apparition has been a poorly placed one. Luckily, we won’t have to wait too long for a better 10P apparition as the 2026 return will be its best since 1967. In 2026, Tempel will pass within 0.41 au of Earth and peak at magnitude 7.5.

Jupiter-family comet 10P/Tempel (formally known as Tempel 2) is now two months past its March 24 perihelion at 1.41 au. The current poor observing circumstances are due to Tempel being located over 2 au from Earth and roughly on the other side of the Sun from our Earth-based vantage point.

No visual observations were submitted to the Comets Section in May. In fact, very few observations have been submitted anywhere with only a single night of May astrometry being published by the Minor Planet Center and no submissions to the COBS site. Mike Olason was able to image the comet from Tucson, Arizona which is quite the feat considering the comet didn’t rise till well after the start of astronomical twilight.

Now post perihelion, 10P should slowly fade in May from magnitude 11.2 to 11.5. Then again, the sparse recent observations suggest it may already be fainter than the prediction. While still predominately a southern object, 10P at least crawls above the horizon before the start of astronomical twilight for northern observers by the end of June.

T = 2021-Mar-24 q = 1.41 au Max El
Jupiter-family comet - 5.4-yr orbital period (deg)
Date R.A. Decl. r d Elong Const Mag 40N 40S
2021-Jun-01 01 48 +02 46 1.583 2.131 44M Psc 11.5 0 25
2021-Jun-06 02 01 +03 36 1.607 2.129 46M Psc 11.5 0 26
2021-Jun-11 02 13 +04 23 1.631 2.126 47M Cet 11.6 0 27
2021-Jun-16 02 25 +05 06 1.656 2.121 49M Cet 11.6 0 28
2021-Jun-21 02 37 +05 45 1.682 2.116 51M Cet 11.7 2 29
2021-Jun-26 02 48 +06 21 1.709 2.109 53M Cet 11.7 4 30
2021-Jul-01 02 59 +06 53 1.736 2.102 55M Cet 11.8 6 31
2021-Jul-06 03 10 +07 22 1.764 2.092 57M Cet 11.8 9 31
Comet Magnitude Parameters --- H = 7.7, 2.5n = 8.1

15P/Finlay – 15P/Finlay was discovered in 1886 by William Henry Finlay at the Royal Observatory at Cape of Good Hope in South Africa. This apparition marks the 16th observed return of 15P. Its best return was in 1906 when it passed 0.27 au from Earth and reached 6th magnitude. During its previous return in 2014/2015, 15P experienced two outbursts of 2-3 mag outburst with the brightest reaching 7th magnitude.

Imaging photometry of 15P reported to the COBS site in May found a comet that was as bright as magnitude 12.5 on May 18 (Michael Lehmann with a 0.2-m reflector). With perihelion on July 13 at 0.99 au, the comet should continue to brighten in June from around magnitude 11.8 (June 1) to 10.5 (July 1). The comet will be a difficult object for northern observers as it moves through the morning sky in Cetus (Jun 1-12), Pisces (12-22), Cetus again (22-26) and Aries (26-30). It will be better placed for southern observers.

Barring any future outbursts, Finlay should peak at magnitude 9.9 at the end of July.

Photo Op Alerts:
June 8/9 with Local Group galaxy IC 1613
June 17 with galaxy NGC 676

T = 2021-Jul-13 q = 0.99 au Max El
Jupiter-family comet - 6.56-yr orbital period (deg)
Date R.A. Decl. r d Elong Const Mag 40N 40S
2021-Jun-01 00 28 -03 48 1.164 1.123 65M Cet 11.8 6 43
2021-Jun-06 00 50 -00 58 1.129 1.105 64M Cet 11.5 7 40
2021-Jun-11 01 13 +01 55 1.098 1.093 62M Cet 11.3 8 38
2021-Jun-16 01 36 +04 47 1.069 1.088 60M Psc 11.0 9 35
2021-Jun-21 01 59 +07 36 1.045 1.089 59M Psc 10.8 10 32
2021-Jun-26 02 22 +10 18 1.024 1.097 57M Cet 10.6 11 30
2021-Jul-01 02 45 +12 51 1.009 1.109 56M Ari 10.5 13 27
2021-Jul-06 03 08 +15 13 0.998 1.127 55M Ari 10.3 15 25
Comet Magnitude Parameters --- H = 9.6, 2.5n = 15.7, offset = +20 days

C/2019 L3 (ATLAS) – C/2019 L3 will be a difficult object to observe in June as it is near solar conjunction. Located in the northern constellations of Perseus (Jun 1-18) and Auriga (18-30), it is not visible from the southern hemisphere. Even northern observers will have difficulty as its elongation stays around 30 degrees. While no observations were reported to the Comets Section in May, a few CCD observations were submitted to the COBS site. The most recent by Thomas Lehmann (magnitude 12.5 on May 23.89 UT) and Steffen Fritsche (12.6 on May 14.87 UT).

C/2019 L3 doesn’t arrive at perihelion till January when it will be 3.57 au from the Sun. The large perihelion distance means C/2019 L3 could remain a visual object well into 2022 and possibly even 2023. If the comet brightens at a conservative 2.5n = 8 rate, it could reach magnitude 10.0 at the end of 2021.

C/2019 L3 (ATLAS)
T = 2022-Jan-09 q = 3.55 au Max El
Long-period comet – Dynamically new (deg)
Date R.A. Decl. r d Elong Const Mag 40N 40S
2021-Jun-01 04 17 +50 15 4.082 4.945 28M Per 12.5 8 0
2021-Jun-06 04 27 +50 07 4.061 4.928 28M Per 12.4 9 0
2021-Jun-11 04 36 +49 59 4.040 4.907 28M Per 12.4 9 0
2021-Jun-16 04 46 +49 50 4.019 4.884 28M Per 12.3 10 0
2021-Jun-21 04 56 +49 41 3.998 4.857 28M Aur 12.3 11 0
2021-Jun-26 05 05 +49 30 3.978 4.828 29M Aur 12.2 12 0
2021-Jul-01 05 15 +49 18 3.959 4.795 31M Aur 12.1 13 0
2021-Jul-06 05 24 +49 05 3.939 4.759 32M Aur 12.1 15 0
Comet Magnitude Parameters --- H = 3.2, 2.5n = 8.0

C/2020 J1 (SONEAR) – SONEAR was discovered on 2020 May 1 by the The Southern Observatory for Near Earth Research (SONEAR) survey which uses two telescopes, a Celestron 11” RASA and 0.45-m f/2.9, located in Oliveira, Brazil. The survey has found 9 comets though only two are named SONEAR, the rest being named after individual observers (Barros, Jacques, and Pimental).

Chris Wyatt visually observed C/2020 J1 on 4 nights between May 13 and 31. SONEAR was estimated by Chris between magnitude 12.6 to 13.0 with a small moderately condensed coma (1.0’-1.8’). Now past an April 18 perihelion (3.36 au), it should slowly fade from magnitude 12.7 to 13.1 as it moves through Libra (Jun 1-13) and Virgo (13-30) in the evening sky.

C/2020 J1 (SONEAR)
T = 2021-Apr-18 q = 3.36 au Max El
Long-period comet – Dynamically new (deg)
Date R.A. Decl. r d Elong Const Mag 40N 40S
2021-Jun-01 14 46 -23 32 3.380 2.435 154E Lib 12.7 26 74
2021-Jun-06 14 35 -21 38 3.386 2.486 147E Lib 12.7 28 72
2021-Jun-11 14 26 -19 47 3.393 2.549 140E Lib 12.7 30 70
2021-Jun-16 14 17 -18 02 3.400 2.624 133E Vir 12.8 31 68
2021-Jun-21 14 10 -16 23 3.408 2.707 126E Vir 12.8 31 66
2021-Jun-26 14 04 -14 52 3.416 2.799 119E Vir 12.9 30 65
2021-Jul-01 13 58 -13 28 3.425 2.897 113E Vir 13.0 29 64
2021-Jul-06 13 54 -12 13 3.435 3.000 106E Vir 13.1 27 62
Comet Magnitude Parameters --- H = 6.7, 2.5n = 8.0

C/2020 R4 (ATLAS) – C/2020 R4 (ATLAS) is now outbound from a March 1 perihelion at 1.03 au and close approach to Earth on April 23 at 0.46 au. Due to a highly retrograde orbit (164 deg) the comet is rapidly moving away from the Earth (1.48 to 2.45 au over the course of June). As a result, the comet has quickly faded from around magnitude 8.4 on May 1.15 UT (Carl Hergenrother) and 8.3 on May 3.92 UT (J. J. Gonzalez) to magnitude 11.6 on May 13.42 UT and 12.4 on May 17.48 UT (later two estimates by Chris Wyatt). This June, it is observable from both hemispheres as an evening object in Leo as it fades from 12th to 14th magnitude.

C/2020 R4 (ATLAS)
T = 2021-Mar-01 q = 1.03 au Max El
Long-period comet –

961-year orbital period (deg)
Date R.A. Decl. r d Elong Const Mag 40N 40S
2021-Jun-01 11 05 +21 50 1.772 1.484 88E Leo 12.2 49 28
2021-Jun-06 11 00 +20 41 1.831 1.651 83E Leo 12.6 43 29
2021-Jun-11 10 57 +19 41 1.890 1.817 78E Leo 13.0 37 30
2021-Jun-16 10 55 +18 47 1.950 1.981 73E Leo 13.3 32 30
2021-Jun-21 10 54 +17 57 2.009 2.140 68E Leo 13.6 28 29
2021-Jun-26 10 54 +17 12 2.069 2.297 64E Leo 13.9 23 28
2021-Jul-01 10 54 +16 30 2.128 2.449 59E Leo 14.1 19 27
2021-Jul-06 10 55 +15 50 2.187 2.596 55E Leo 14.4 16 25
Comet Magnitude Parameters --- H = 8.9, 2.5n = 10.0

C/2021 A1 (Leonard) – C/2021 A1 (Leonard) was found on 2021 January 3 by Greg Leonard with the Mount Lemmon 1.5-m reflector. At discovery, it was around 19th magnitude and located 5.1 au from the Sun. According to the most recent published orbit by Syuichi Nakano (Nakano Note 4460, s/nk/nk4460.htm), Leonard has an “original” orbital period of

90,000 years suggesting it is a dynamically old long-period comet.

As we mentioned in the previous few ALPO Comet News, C/2021 A1 has the potential to become a nice object at the end of the year. It has a few things going for it including 1) a relatively small perihelion of 0.62 au on 2022 January 3, 2) a close approach to within 0.233 au (34.9 million km or 21.7 million miles) from Earth on December 12, and 3) a phase angle that reaches a maximum of 160 degrees at the time of close approach. The high phase angle may result in a few magnitudes of enhanced brightness due to forward scattering of light by cometary dust.

Now a few things working against it. High phase angles also mean small solar elongations. A minimum solar elongation of 15 degrees occurs at the time of highest phase angle and greatest forward scattering. 15 degrees solar elongation is similar to that of C/2020 F3 (NEOWISE) on 2020 July 5. While NEOWISE was definitively observable at that time and even naked eye from the clear skies of Tucson, it was just barely so and NEOWISE was around magnitude 1.5 to 2.0 at the time. If C/2021 A1 is fainter, it would be a difficult object for many even with optical aid.

How bright C/2021 A1 will get at that time is very uncertain. The increase in brightness due to forward scattering could be up to 2-3 magnitudes but that depends on how dusty the comet is. If it is gas-rich, meaning dust-poor, forward scattering could be much less. Also, while C/2021 A1 brighten rapidly between April 2020 and March 2021, its rate of brightening has stalled since mid-March. A conservative 2.5n = 8 rate of brightening from now through perihelion results in a peak around magnitude 6.5 without any forward scattering. Even with significant forward scattering, that’s only a peak around magnitude 3.5. That would be a wonderful comet at 90, 60, or even 30 degrees from the Sun, but it would be a difficult sight at 15 degrees solar elongation. Hopefully the comet appeases us Earth-bound observers by kicking its brightening trend into high gear.

Like last month, the comet is still an evening object near 17-18th magnitude located up north in Ursa Major. Imagers are strongly encouraged to monitor C/2021 A1 over the coming months.

C/2021 A1 (Leonard)
T = 2022-Jan-03 q = 0.61 au Max El
Long-period comet – Dynamically old (deg)
Date R.A. Decl. r d Elong Const Mag 40N 40S
2021-Jun-01 10 41 +57 10 3.455 3.623 72E UMa 17.6 55 0
2021-Jun-06 10 37 +56 16 3.395 3.628 68E UMa 17.5 51 0
2021-Jun-11 10 34 +55 20 3.335 3.631 65E UMa 17.5 47 0
2021-Jun-16 10 31 +54 24 3.275 3.632 61E UMa 17.4 43 0
2021-Jun-21 10 30 +53 28 3.214 3.630 58E UMa 17.3 39 0
2021-Jun-26 10 28 +52 32 3.153 3.624 55E UMa 17.3 36 0
2021-Jul-01 10 28 +51 36 3.091 3.614 51E UMa 17.2 33 0
2021-Jul-06 10 28 +50 40 3.029 3.601 48E UMa 17.1 30 0
Comet Magnitude Parameters --- H = 10.5, 2.5n = 8.0

New Discoveries, Recoveries and Other Comets in the News

99P/Kowal – Michael Kelley reported a small

0.7-magnitude outburst of short period comet 99P/Kowal between May 12 and 14. The detection was made with the Oschin 1.2-m Schmidt on Mount Palomar and the GROWTH India Telescope (GIT) 0.7-m telescope. 99P/Kowal is a year out from a 2022 April 12 perihelion at 4.71 au and is currently around 17-18th magnitude. [Ref: ATel 14628]

C/2021 K1 (ATLAS) – A new 16th magnitude comet was detected in images taken on 2021 May 14 and 24 by the Asteroid Terrestrial-Impact Last Alert System (ATLAS) with their 0.5-m f/2 astrographs on Mauna Loa and Haleakala. Several PANSTARRS pre-discovery observations have been found back to April 2020 when the comet was 21st-22nd magnitude. C/2020 K1 is a periodic comet with an orbital period of 45.6 years. Perihelion was on 2021 May 4 at 2.50 au. Though post perihelion, minimum distance to the Earth occurs in mid-September at 1.87 au. The comet should peak at slightly brighter than 16th magnitude from June to September. Its next perihelion won’t be till August 2065. [Ref: CBET 4968 & MPEC 2021-K89]

P/2021 J3 (ATLAS) – The ATLAS 0.5-m f/2 astrograph on Mauna Loa first detected this 18th magnitude comet on May 13. CBET 4974 reports that Syuichi Nakano has determined a short-period orbit for P/2021 J3 with an orbital period of 26 ± 1 year. Perihelion was almost two years ago on 2019 July 1 at 4.92 au. It is interesting that a 18th magnitude comet is found 2 years after perihelion. Last year at opposition, the comet was located in the dense star fields of Sagittarius perhaps explaining why it wasn’t detected then. But go back another year to 2019 when the comet was at perihelion and should have been even brighter than 18th magnitude, and P/2021 J3 was well clear of the Milky Way and should have been easily detectable. It is very possible that the latest ATLAS comet is experiencing an outburst. [Ref: CBET 4974 & MPEC 2021-L26]

C/2021 J2 (PANSTARRS) – The Pan-STARRS1 telescope on Haleakala, Maui, discovered this 21st magnitude comet on May 10. This is a distant long-period comet with perihelion on 2021 September 21 at 4.71 au. CBET 4973 reports that Syuichi Nakano determined an osculating orbital period of

1300 years. Though faint at 21st magnitude, the comet is past opposition and likely to become fainter with time. [Ref: CBET 4973 & MPEC 2021-L24]

C/2021 J1 (Maury-Attard) – This comet is the first discovery of the MAP project whose moniker is derived from the last names of its participants, Alain Maury, Georges Attard and Daniel Parrott. The MAP program used a Celestron RASA 11” located at San Pedro de Atacama in Chile to find C/2021 J1 on May 9 at 19th magnitude. Alain Maury is no stranger to comet and asteroid discovery. He was part of the Second Palomar Sky Survey in the late 80s as well as the ODAS (OCA DLR Asteroid Survey) in the late 90s. During those surveys, Alain was part of the discovery of 3 comets: C/1988 C1 (Maury-Phinney), 115P/1985 Q1 (Maury), and 198P/1998 X1 (ODAS). Daniel Parrott is the author of the Tycho Tracker software that utilizes GPUs to “stack-and-shift” images at different possible motions to detect moving objects in a sequence of images, a technique also known as synthetic tracking. More on the MAP survey can be found at https://www.spaceobs. aury-s-Blog/MAP.

C/2021 J1 is a Halley-type comet with an orbital period of 135 years and inclination of 92 degrees. Perihelion occurred back on 2021 February 19 at 1.74 au. As a result, the comet is fading from its current 19th magnitude. Its location at -56 degrees declination and southerly motion means observations will be limited to the southern hemisphere. [Ref: CBET 4972 & MPEC 2021-L11]

C/2021 G1 (Leonard) – Greg Leonard of the Catalina Sky Survey found this 21st magnitude comet on 2021 April 11 with the Mt. Lemmon 1.5-m reflector. A retrograde comet with an orbital period of

650 years, Leonard comes to a rather distant perihelion on 2021 July 22 at 3.42 au. It likely has already peaked in brightness at around 20-21st magnitude. [Ref: CBET 4959 & MPEC 2021-J72]

C/2021 E3 (ZTF) – The Zwicky Transient Facility used the 1.2-m Oschin Schmidt to detect this object as an asteroid on 2021 March 9 at 19th magnitude. Follow-up observations detected cometary activity resulting in its announcement as comet C/2021 E3 (ZTF). Perihelion occurs next year on 2022 June 11 at 1.78 au. A conservative 2.5n = 8 brightening coefficient results in a peak brightness of a little brighter than magnitude 12 in May and June of 2022. At that time the comet will reach a minimum distance to Earth of 1.21 au and located deep in the southern sky (passing within 10 degrees of the South Celestial Pole). If C/2021 E3 brightens faster than expected it could be a visual object for southern observers in mid 2022. [Ref: CBET 4960 & MPEC 2021-J71.

C/2020 PV6 (PANSTARRS) – Similar to the above object, C/2020 PV6 was originally reported and announced as an asteroid. The Pan-STARRS project discovered PV6 on 2020 August 13 at 21st magnitude. A number of imagers have detected cometary activity in May 2020. According to Syuichi Nakano, the comet is long-period object with a period of

270 years. Perihelion occurs in a few months on 2021 September 25 at 2.30 au. Peak brightness should be around magnitude 15.0 in July. [Ref: CBET 4969 & MPEC 2021-K93]