See Comet Leonard at its Best

By: Bob King December 3, 2021 22

The year’s brightest comet is now on display in the pre-dawn sky this week and next. Here’s how to find it.

Comet Leonard and M3 — Comet Leonard makes a spectacular pairing with the bright globular cluster M3 in the constellation Canes Venatici on December 3, 2021.
*Martin Mobberley*

Go out the next clear night or you might miss it! Northern Hemisphere skywatchers have a limited window in which to view Comet Leonard (C/2021 A1), which will likely become the brightest comet of the year. The good news is that while time is short, Leonard is expected to reach peak brightness during the next two weeks. Currently a binocular object around magnitude 7, the comet could become as bright as 5th magnitude as it travels eastward across Boötes, Serpens, and Ophiuchus in the predawn sky.

Comet Leonard orbit — Comet Leonard's orbit takes it out to the Oort Cloud, a roughly spherical repository of billions of comets that orbits the Sun out to nearly a quarter the distance to the Alpha Centauri star system. Leonard has traveled about 3,500 a.u. for a brief spin around the inner solar system before returning to this frozen fastness. Its position is shown for December 12th, when it comes closest to the Earth.
*NASA, JPL Horizons*

Senior research specialist Greg Leonard at the Mt. Lemmon Observatory near Tucson, Arizona, discovered the comet on January 3, 2021, when it was little more than a faint, distant speck. Since then, it's inched steadily closer to both the Sun and Earth and will reach perihelion — closest approach to the Sun — on January 3, 2022. Three weeks prior, on December 12th, it will pass nearest the Earth at a distance of 21.7 million miles (34.9 million km).

While Comet Leonard won't compare to the splendor of last July's Comet NEOWISE, it's likely to become faintly visible with the unaided eye from a dark sky within a few days of December 12th. That also happens to be the the date, give or take, that it will succumb to the glare of morning twilight low in the eastern sky. You'll see it best with a pair of binoculars or a telescope from locations with a dark eastern sky. Use this light pollution map to help you locate the best spot in your city or region. Fortunately, the Moon will be around new phase and not a concern.

Comet Leonard Finder Chart — Use this finder chart to locate Comet Leonard. Dates shown are for 0h UT. If you live in the Eastern Time Zone, subtract 5 hours; 6 hours for Central; 7 hours for Mountain and 8 hours for Pacific. For example, December 9th, 0h UT = December 8th at 7 p.m. EST. Click on the image or here for a larger version.
*Sky & Telescope*

What will we see? Comets can be tricky to predict because they have a penchant for unpredictability. Composed of fragile honeycombs of ices both exotic and familiar, they sometimes break apart when nearing the Sun. Solar heating vaporizes the ice, creating pressures within and without the comet's body that can sometimes disrupt it, tearing it apart.

Comet Leonard Dec. 3, 2021 — This view of Comet Leonard, made on December 3, 2021, with a 70-mm f/2.8 lens at ISO 6400 and a 10-second exposure, more closely resembles its telescopic appearance under a dark sky.
*James Schaff*

It's even possible that something of the sort is happening right now with Leonard — after steadily brightening, it has recently shown signs of plateauing. Assuming its nucleus hangs together, binoculars should reveal the coma as a soft patch of light, brighter toward the center, about half the Moon's apparent diameter. With averted vision you may glimpse a degree or more of faint tail pointing upward to the northwest.

Keep a close eye on Leonard on as many mornings as possible. Should the nucleus break apart due to solar heating or other forces, it could experience a modest outburst and then fade rapidly. Contrariwise, forward scattering from cometary dust, as discussed in this previous article, could temporarily pump up its brightness and guarantee a naked-eye view. We wait with bated lens and telescopes to see what Leonard's next move will be.

Location of Comet Leonard Dec 10-13 — Comet Leonard races across Serpens and into Ophiuchus during its last mornings of visibility before transitioning into evening twilight.
*Sky & Telescope*

As the comet is now quickly approaching both the Earth and the Sun, it's speeding faster across the sky. For the next few mornings (through December 8th) you'll find it in the constellation Boötes, not far from the brilliant, orange giant Arcturus. Hold this star's hand, and you'll have an able guide to Leonard. On Saturday morning, December 4th, the comet stands 8.5° to the star's upper left and just 5° away on the 6th. Although the comet's altitude decreases each morning, this may be offset by its growing brightness. Peak magnitude around 4.5–5 is expected from about December 10th to December 15th.

Staring on around December 12th, Leonard swings into the evening sky and slowly distances itself from the Sun while also fading. This is when Southern Hemisphere observers will have the best view, while dusk will likely swallow the sight for northerners. I made my last Leonard observation in 10×50 binoculars and a 15-inch telescope during the November lunar eclipse. With the moon tucked deeply in shadow at mid-eclipse, I stole views of its fluffy coma, compact "fuzzy-star" nuclear region and lovely degree-long tail.

Location of Comet Leonard Dec 14-22 — Now Comet Leonard is an evening target. Note: The dates with the comet symbols are for 0:00 Universal Time, which in North America falls on the evening of the previous date. So, for instance, the "18" here means the evening of December 17 in North America.
*Sky & Telescope*

As I write this, I'm on a cruise ship speeding northeast at 15 knots an hour toward the centerline of the December 4th total solar eclipse. With luck, we'll arrive under clear skies near South Georgia Island off the coast of South America and, if successful, I hope to share photos of the singular event tomorrow right here.

I mention my location and purpose because from latitude -60° south Comet Leonard is burrowed deep below my horizon. And by the time I return home it will be lost in twilight glare. I encourage all of you fortunate enough to be in the right place to take advantage of your viewing opportunities. Find a dark location and seek this dusty phantom that has finally arrived at your door after a 35,000-year pilgrimage from the outer solar system. Oh and please say "hi!" for me.

Comments

Chris-Schur

December 3, 2021 at 3:20 pm

Enjoy the eclipse Bob! You will have to tell us all about it when you return. We had a beautiful shooting session on the comet and M3 this morning from Arizona, going for the best composition possible. Tomorrow morning will be equally spectacular - TWO globulars in the same field! Dont you just love comets?!

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Bob KingPost Author

December 3, 2021 at 4:14 pm

Sounds wonderful, Chris. Go for that globular two-fer! Hopefully, we'll have clear skies and I can share an image or two.

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Bdoc123

December 4, 2021 at 5:10 pm

Excellent! I will look for it. By the way, I think you are on the same cruise as a meteorology friend of mine. His name is Joe Rao. If you know him, tell him I said "Hello!". Have a great time!

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Rod

December 3, 2021 at 7:05 pm

I viewed M3 and comet Leonard this morning 0500-0600 EST in MD. I placed a report note here, https://skyandtelescope.org/astronomy-news/this-weeks-sky-at-a-glance-december-3-11/

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New Jersey Eclipse Fan

December 4, 2021 at 2:08 pm

Thanks for the latest info and also your comment on last week’s S&T stream about viewing Orion and Sirius from Jerusalem, which is 21km from my current location. In fact, I’m about to go outside and “look up,” since it’s already nighttime in Israel!

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Bob KingPost Author

December 4, 2021 at 6:44 pm

Thank you, Rod for your note.

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OwlEye

December 3, 2021 at 7:09 pm

Hi Bob,

If I had known this morning that you were not in the northern hemisphere, I'd have said hello to Leonard for you! Some morning soon, though!

After checking the comet's position last night relative to M3, it looked like they would be just under a degree apart by the beginning of astronomical twilight this morning. The 12.5-inch f/10 with a 40mm, 72 degree field SWAN eyepiece yields 79 X and a 0.9 degree actual FOV, and at 5:50 am local today, I had the tail of Leonard poking into the FOV with a largely resolved Messier 3 tangent to the opposite side. Just spectacular!!

Leonard had grown so much larger and brighter since my last view on November 26th, more than tripling in coma diameter and a magnitude increase from ~ 8.0 to ~ 6.7. In spite of my light polluted eastern sky, I'm seeing quite a bit, and the changes are fascinating to watch. Fun mornings ahead keeping up with it's acceleration toward the eastern horizon.

Hope you have clear skies tomorrow!

Regards,
DZ

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William

December 5, 2021 at 9:39 pm

Thanks for this info, Bob ! With this S&T finder chart .. I finally saw C/2021 A1 Leonard this morning, at about 4:30AM... from a less than ideal (semi dark) location, in our municipality here in the Philippines. I used Canon 15x45 IS binoculars.. and detected the non stellar glow (not well defined), after I was fully dark adapted. The comet had a slightly brighter (very tiny) core area, which I estimated at around mag 7. It is possible, I was viewing the comet through some very thin pre dawn clouds.

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Bob KingPost Author

December 6, 2021 at 8:51 pm

Hi William,

You're welcome and your observation is much appreciated. Did you by chance observe a tail?

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bob kelly

December 7, 2021 at 8:14 am

for what it is worth - I took some photos through some cirrus here near NYC this morning. The comet looked about the same brightness (in the photos) as nearby 7th magnitude stars.
Photo at https://bkellysky2.wordpress.com/2021/12/07/i-caught-the-comet-in-a-really-underwhelming-photo/

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Zubenelgenubi 61

December 6, 2021 at 6:26 pm

Comet Leonard was a dismal performer for this Bortle 7-8 sky dweller this morning. I decided not to head to a darker location, since the temperatures were cold and windy and the clouds iffy. Not visible to naked eye, not visible in binoculars, and just a dim tailless fuzzy spot in a couple of images. Some high thin clouds did interfere at times. I would say that it couldn't have been brighter than 7th mag, but of course anything but the innermost coma would have been blotted out by the lights. Unless there is a large enhancement due to the forward scattering, there is little hope of any evening show, except for imagers, who can make lemonade out of lemons.

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Bob KingPost Author

December 6, 2021 at 8:50 pm

Hi Zuben,
I wondered whether the comet might continue to stall in brightness. Thank you for your valuable if concerning observation. Sadly, these are the skies many people must observe under.

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Zubenelgenubi 61

December 7, 2021 at 11:26 am

The sketchy weather forecast did not justify an early morning, very cold trip to a dark site. I do hope to go if we get a clear forecast before Leonard leaves the morning sky. NEOWISE stood out well in binoculars even from my bad location, but this one is about 100 times dimmer. Would that we could get something like Hale-Bopp or Hyakutake, with today's imaging capabilities!

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Scott2112

December 8, 2021 at 10:34 am

I am sharing some of Bobs' misfortune although mine is meteorological. Clouds have dominated for some time here in Southern Ontario, and although there make be a brief respite on Sunday, it may be too late by then. I'll have to live vicariously through the eyes and scopes of the rest of you.
Scott

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Rod

December 9, 2021 at 7:55 am

FYI, here is another comet Leonard observation report from me for this morning. [Observed 0445-0545 EST/0945-1045 UT. Sunrise 0713 EST/1213 UT. First Quarter Moon 11-Dec-2021 0136 UT. I viewed comet Leonard again this morning using 10x50 binoculars and 90-mm refractor telescope using 14-mm eyepiece at 71x. This is my third comet observation of Leonard since 01-Dec-2021. The telescope eyepiece true FOV a bit more than 1-degree (60 arcminutes). The comet was a distinct fuzzy in 10x50 binoculars and in the telescope view, showed a large fuzzy coma with hint of tail at 71x. 9th-11th magnitude stars visible in the telescope view, Starry Night and Stellarium sky charts showed these. Two stars stood out about 48 arcminutes angular separation from the comet to the right or so of the comet, north up, mirror reverse view. In 10x50 binocular view, they were to the left or so of the comet. Tau4 Serpentis and HIP76438 easy to see 44 to 48 arcminutes angular separation from comet Leonard according to Stellarium 0.21.2 angle mode and Starry Night Pro Plus 8. Stellarium and Starry Night show both stars magnitudes 6.50 and 7.05/7.06. Stellarium and Starry Night indicated comet Leonard magnitude 4.72 but theskylive.com site reports 6.7. 6.7 apparent magnitude looks more accurate in my telescope view. This was an enjoyable comet observation early this morning with temperature -3C, winds WNW 4 knots and clear skies. After coming back inside, the wood burning stove felt good along with hot coffee ]

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bob kelly

December 9, 2021 at 10:29 am

Just a fuzzy spot in the camera here in lower Westchester, NY.
This morning's photos at https://bkellysky2.wordpress.com/2021/12/09/comet-leonard-tries-to-hide-behind-a-utility-pole/
bob k

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TomR

December 10, 2021 at 6:29 am

Wednesday morning I had good luck with the weather. Starting from Arcturus I could easily find the comet in binoculars. I would estimate a magnitude around 6.

“Hello from Bob King!”, I said to the cosmic visitor. He replied something in a strange language. I think he wanted to express: “Say also Hello to Bob King and a Merry Christmas to everyone!”

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Warren-Odom

December 14, 2021 at 8:16 pm

Just a minor thing - FYI, "15 knots per hour" is redundant. "Knot" means "nautical mile per hour" so the correct expression for your ship's speed is "15 knots."

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December 16, 2021 at 3:44 am

I believe I spotted Comet Leonard this evening (12/15) at 6:45 PM from where I live about 15 miles west of Honolulu, using 8x42 binoculars. Looked like a faint fuzzy patch; the sky wasn't fully dark. Should have waited a while for it to get darker but earthly business intervened!

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Alan MacRobert

December 20, 2021 at 6:25 pm

Dec. 20: Spotted it pretty easily with 10x50 binoculars in late twilight from latitude 42.4 N. I got it at 5:21 p.m. EST, a small fuzzpatch with a subtle but definite averted-vision tail, a fraction of a degree long, in the correct direction. It got plainer to see in the next 5 minutes before going behind the distant treeline of pines.

Those 5 minutes ran from 71 to 76 minutes after sunset, as the comet's altitude went from 6 degrees to 5.3 degrees, and the Sun's altitude below the horizon went from -11.7 degrees to -12.5 degrees. Some people are reporting the comet as brighter than it was predicted to be by this date.

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Rod

December 20, 2021 at 7:33 pm

Here in Maryland, I tracked the comet down using 10x50 binoculars, more distinct near 1745 EST. I posted an update report for this evening at the link, https://skyandtelescope.org/astronomy-news/this-weeks-sky-at-a-glance-december-17-25/#comment-381871

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