Has our bright comet drought ended? Find out when and where to see the brightening Comet ATLAS (C/2019 Y4).

Comet ATLAS (C/2019 Y4)
Comet ATLAS (C/2019 Y4) displays an 8.5-magnitude coma and a short, spiky tail on March 21, 2020. Discovered last December, the comet has brightened rapidly in recent weeks. North is up.
Chris Schur

Not since Comet 46P/Wirtanen passed near the Pleiades star cluster in December 2018 has a naked-eye comet graced the night sky. That may soon change. On December 28, 2019,  astronomers with the automated Asteroid Terrestrial-impact Last Alert System (ATLAS) survey discovered a 20th-magnitude comet in Ursa Major that was subsequently named Comet ATLAS (C/2019 Y4).

Comet ATLAS trajectory
Comet ATLAS’s orbit is tilted 45° with respect to the plane of the planets. Closest approach to the Earth occurs on May 23rd (116.7 million kilometers), prior to its May 31st perihelion.
NASA / JPL Horizons

Once a reasonable orbit was determined, Comet ATLAS proved a close match to the Great Comet of 1844 (C/1844 Y1). Both have periods around 4,000 years, approach within 0.25 astronomical unit (a.u.), or 37.4 million kilometers, of the Sun at perihelion, and are inclined 45° to the ecliptic. These and other orbital similarities were strong enough to conclude that both objects were fragments of a single, much larger comet that broke apart about 5,000 years ago. For all we know there may be additional fragments en route for future appearances.

Comet ATLAS (C/2019 Y4)
Glowing aqua from carbon and cyanogen emissions and sprouting a 15′ long tail, Comet ATLAS passes near Rho (ρ) Ursae Majoris on March 22nd. Its coma has ballooned in recent days to 15′ across, which at its current distance is equal to half the size of the Sun. South is up.
Gerald Rhemann

Because the Great Comet reached 2nd magnitude and grew a 10° tail in January 1845 many of us wondered if its sibling might be capable of doing the same. The answer is a qualified "yes." But one thing is certain — the comet is brightening exponentially.

A Brightening Comet

Back on February 16th, Comet Atlas was a 14th-magnitude wisp 30″ across and barely brighter than the sky background through my 15-inch telescope. Three weeks later on March 6th the coma had grown to about 5′ and become more compact with a magnitude of 11. By mid-March I snared it with a pair of 10×50 binoculars at magnitude 9 from a dark-sky site. Other observers have reported a similar rapid uptick.

To highlight Comet ATLAS's motion, 151 images taken on March 18th were combined to create this video.
Shigemi Numazawa

How Bright Will Comet ATLAS Be?

While a hundredfold increase in brightness in a month makes a comet lover's heart palpitate, it could also mean that the comet's volatile ices are rapidly vaporizing as it nears the Sun. Once those materials are depleted some astronomers expect Comet ATLAS's brightness curve to flatten out, a common occurrence in comets that have rarely or never come close to the Sun before. Long-period comets that approach within 1 a.u. of our star have been known to split apart, disintegrate, and disappear. Comet ISON (C/2012 S1) offers a classic example. Shortly before its November 2013 perihelion, the comet crumbled into a cloud of dust and ice, dashing hopes for the spectacle so many of us had anticipated.

Comet ATLAS finder chart
The chart shows the position of Comet ATLAS (C/2019 Y4) through April 24th at 0h UT for the dates shown. Click the image for a black-and-white PDF of the chart. As the comet approaches perihelion, we'll be providing updated charts.
Sky & Telescope

According to NASA’s JPL Horizons the comet could reach magnitude –5, exceeding Venus in brightness at perihelion on May 31st. Because it will lie 13° southwest of the Sun at that time, it might be possible to see the object in broad daylight with a properly shielded telescope.

That prediction may be overly optimistic however. In a March 19th notice from the Central Bureau for Astronomical Telegrams (CBAT), Director Daniel Green applied a formula based on the behavior of previous long-period, Sun-hugging comets and derived a more conservative peak magnitude of –0.3.

It's good news either way. In both predictions Comet ATLAS will reach naked-eye brightness in mid-May before it's lost in the solar glare. The JPL Horizons formula predicts a peak magnitude between 1 and 2, while Green anticipates that number to be between 2 and 3. During the first half of May the comet will appear low in the evening sky at dusk and early nightfall as it tracks through Perseus. Binoculars should reveal a bright, strongly condensed coma followed by dust and gas tails pointing away from the Sun. With a little luck we might even see the tail without optical aid.

After rounding the Sun, Comet ATLAS returns to view around June 15th at dawn in Orion for Southern Hemisphere skywatchers. Initially glowing at magnitude 3 or 4, the comet will fade quickly — assuming it survives a sizzling perihelic encounter!

How to See Comet ATLAS

Comet ATLAS (C/2019 Y4) sketch
On March 21.2 UT I observed Comet ATLAS in 10×50 binoculars . The sketch conveys its faint, diffuse appearance at the time. I estimated the comet's magnitude at 8.5 with a coma diameter of 12′ and DC (degree of condensation) of 2.
Bob King

For now, observers in the Northern Hemisphere can follow the comet from Ursa Major through Camelopardalis with a 6-inch or larger telescope. While visible in binoculars the comet is still quite diffuse and takes some effort to see. That should change soon.

In a telescope, Comet ATLAS shows a large, diffuse coma with a small, more compact knot at the center dotted with a faint, starlike nucleus. If you have a Swan band filter, which enhances carbon emissions from gas-rich comets, you'll find that Comet ATLAS responds well. I noted a distinct increase in the comet's contrast and visibility through the filter this month.

And what would comet-watching be without a picturesque "deep-sky drive-by" or two? Watch for Comet ATLAS to buzz within a degree of the galaxy NGC 2366 on April 3rd and pass directly in front of the pretty open cluster NGC 1545 in Perseus on May 14th.

Comet ATLAS (C/2019 Y4) trajectory
Comet ATLAS's trajectory is shown here starting several years before discovery (nested loops, left), and during the current apparition with markers every seven days, going several years into the future (nested loops, right).
Tom Ruen

The comet remains a circumpolar object for much of the U.S. and Europe until about two weeks before perihelion, when best viewing will be during the early evening hours. If the comet is especially dusty, we'll likely see a more spectacular tail instead of a bright, spiked fuzz ball. Be hopeful, but as always when it comes to these fragile objects, temper your expectations.

As Comet ATLAS approaches perihelion, I'll update with new maps and information. I'd love to hear what you're seeing and encourage you to share your observations and thoughts in the comments section. We all need some good news right now given the havoc wrought by the coronavirus. Comets have traditionally been viewed as bearers of malevolence throughout much of human history. In a twist of irony this latest emissary from the remote depths of the solar system may offer a needed dose of wonder.

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Comments


Image of Tom-Reiland

Tom-Reiland

March 26, 2020 at 4:47 am

I got my second observation of Comet Atlas 2019/Y4 in both the 21" Newtonian and the 5" Refractor last night at Wagman Observatory. The coma was more concentrated towards the center with a star-like nucleus. Later, I was able to spot it through my 10 X 50 binocs, just barely. I made a second binocular observation 90 minutes later to confirm my first one. My rough estimate of the magnitude is between 8.5 to 8.0 magnitude. My observation on March 1 put it at 11.5 to 12.0 magnitude and it was a much smaller, diffuse, round patch. The sky contrast was not exceptional, but it was better than the previous week. I would love to see it turn into a great morning comet similar to Comet West in 1976. The was the first spectacular comet that I observed. Later, I was able to view 3 of the 4 pieces of the nucleus after it broke up.

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Bob King

March 27, 2020 at 2:16 pm

Hi Tom,
I concur with your binocular estimate. I got 8.3 last night (March 26-27) in my 10x50s. West was my second spectacular comet. First was Bennett in 1969. Spring seems to be a happy time historically for bright comets for northern hemisphere observers. Just coincidentally of course.

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Tom-Reiland

March 30, 2020 at 3:59 am

I did not want to go to Wagman Obs tonight because of the late Moonset and the wind. I decided to set up my 5" f/5 Jaegar's Refractor in my backyard to see if I could locate Comet ATLAS c/2019 Y4. I went outside after 2:30 AM and started to hunt it in Camelopardalis near the border with Ursa Major and not far from M81 and M82.
I used 20mm and 18mm eyepieces (31X & 35X). I located it about 2:45 AM, but it was not easy to see because of the LP in Shaler. What a difference 11 driving miles make. It's still around 8 to 8.5 magnitude. There was no way that I could see the comet through my 10 X 50 binocs, though I tried.

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FifthWheelFollies

March 27, 2020 at 4:45 pm

I saw Bennett. Luckily, I had an early morning newspaper route at the time. I looked up and there it was. Very big and looking like it was going somewhere. Ranks up there with total solar eclipses on my must see list.

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Bob King

March 29, 2020 at 8:33 pm

Totally agree, Fifthwheel. Gorgeous spring sight!

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Rod

March 26, 2020 at 9:49 am

In Maryland, I may get a view next Monday night when the skies are mostly clear. I plan to view using my 10-inch telescope and perhaps, near 0600 EDT on Tuesday morning, see Mars and Saturn close conjunction in Capricornus too 🙂

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Bob King

March 27, 2020 at 2:16 pm

Good luck and clear skies, Rod!

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John Rombi

March 27, 2020 at 5:21 pm

It's a shame that we won't see it in the SH....Many comments are made about "other" bright comets. Not much is said about Comet McNaught 2007. This was a daytime object.

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Bob King

March 28, 2020 at 8:51 pm

Hi John,
It was even beautiful here in the NH before it came to you. Fantastic comet equal to Hale-Bopp for southern hemisphere observers.

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Zubenelgenubi 61

March 26, 2020 at 6:43 pm

I really hope this is not confirmed to be the case, but the date of brightening appears to have slowed down in the last week or so. The supposed surge may have been due to the comet becoming bright enough for observers to include the outer parts of the coma in their estimates. Now that this has been factored in, the brightness curve is flattening out.

Since the comet is already eighth magnitude, it is likely to attain marginal naked eye visibility- perhaps a fuzzy spot like Wirtanen. I would be happy if the comet could attain even the CBAT level of brightness. It could be an interesting sight to the right of Venus in the mid-May western skies, but I don't expect greatness. I hope I am wrong, though.

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Bob King

March 27, 2020 at 2:19 pm

Hi Doug,
I am trying to keep that attitude too about this comet, the reason I choose not to overplay bright expectations in the article. Already however ATLAS is brighter than C/2017 T2. Last night I used the Swan filter again and the contrast gain and coma expansion were considerable.

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Joe Stieber

March 29, 2020 at 12:58 am

I finally got my first view on Friday evening, 27-March-2020. I picked it up with 15x56 binoculars at 8:55 pm EDT in the New Jersey Pines. That was five minutes after the end of astronomical twilight when there was still a 12% illuminated moon low in the west. Transparency was good, but not great, between passing cirrus clouds.

As I usually try to do, I found it without a looking at a finder chart. I just remembered from that afternoon when I was preparing charts that it would be about a binocular field left of the compact triangle formed by Rho, Sigma¹ and Sigma² UMa. Indeed, that's where I spotted a vague patch of haze, which I then confirmed as C/2019 Y4 with my charts.

I can see where those who don't follow comets too closely and are now looking at Y4 because of all the press about it might be a little disappointed. Fingers crossed that its appearance will change dramatically for the better in May, but in the meantime, I'm keeping my expectations in check.

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Bob King

March 29, 2020 at 12:10 pm

Hi Joe,
Thanks for sharing your report. For regular comet watchers ATLAS is coming along nicely, but for a typical skywatcher with compromised skies and a small telescope it's still a "faint, fuzzy patch". I was heartened to see how much more compact its core has become in recent days. I also spotted the tail spike projected across the coma.

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Dave Mitsky

March 29, 2020 at 2:00 pm

I brought my 15x70s with me to the orange-zone Naylor Observatory on the night of March 15th hoping to see Comet C/2019 Y4 (ATLAS) but the sky was just not dark enough. However, I was able to locate the comet with the observatory's 17" f/15 classical Cassegrain at 170x but it wasn't more than a faint fuzzball. I also viewed the comet at 116x and 216x, with the latter providing the best view. I was unable to detect it with the 5" f/5 finder scope

https://www.heavens-above.com/comet.aspx?cid=C%2F2019%20Y4&lat=40.1469&lng=-76.8989&loc=Edward+L.+Naylor+Astronomical+Center+%26+Observatory&alt=170.0&tz=EST

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Bob King

March 29, 2020 at 5:59 pm

Dave,
Sounds like bad light pollution but it's a good check on expectations because so many observers live under similar skies. Thank you!

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OwlEye

March 29, 2020 at 11:26 pm

Hi Bob,

I finally got some reasonably clear sky this evening, and even with some light cirrus and the moon over 5.5 days old, comet ATLAS had gotten a bit brighter than my first observation on the evening of March 20th. I, too, noticed the inner coma had gotten more compact and at times, using fixed averted vision, I believe I caught a fleeting twinkle of the nearly-stellar false nucleus. Again, as on the 20th of March, my best view was at 76 X in the 6-inch reflector. The coma was ~ 6' in diameter (not bad in the moonlight and thin cirrus!).

Regards,
Doug Z

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