Comet 45P Returns to Dark Skies

After battling moonlight, Comet 45P/H-M-P returns for a final go-round in dark skies. Even better, it's up by 10 o'clock!

Update (February 15, 2017): Arecibo Observatory has captured radar images of Comet 45P/Honda-Mrkos-Pajdusakova. It's only the seventh comet to be imaged using radar because comets rarely come close enough to Earth. Scroll down to see the radar image.
Fuzzy Comet 45P/HMP, Fainter Than Expected

Chris Schur of Payson, Arizona, took this portrait of 45P/Honda-Mrkos-Pajdusakova on the last moonless morning (February 8th). The coma appeared diffuse with a brighter center.
Chris Schur

It's rare for a comet to transition from pre-dawn object to evening target in only six days, but 45P/Honda-Mrkos-Pajdusakova's proximity to Earth made all the difference. When it passed only 7.7 million miles above our rooftops on February 11th, the green blob briefly sped across the sky at up to 9° a day.

Lucky for us, it's been traveling west towards evening, while the Moon's been moving east. That's why, starting tonight, 45P/H-M-P will once again be visible in a moonless sky. On the evening of February 14th, the comet will stand about 10° high in the northeastern sky just before moonrise. Depending on your latitude, you might get as little as 10 minutes up to a half hour of dark sky. Things quickly improve later in the week as 45P rapidly gains altitude as the Moon rises later and later.

45P/H-M-P got a lot of hype last week; unfortunately, the bright Moon put the kibosh on viewing such a diffuse object for small scope and binocular users. Not only that, but the comet wasn't as bright as expected. Some predicted a peak magnitude of around +6.5, but it never got brighter than +8. Such is the nature of these cosmic fuzzballs. They can thwart our expectations, follow due course, or put on a surprise show.

Farewell to Earth, See You Again in 5.25 Years!

This diagram shows the comet's current position relative to Earth on February 14th. It's still in the neighborhood and a fine observing target. The comet's arc of motion is shown with dark blue indicating its travels south of the ecliptic plane and light blue, above.
NASA / JPL, with additions by the author

As we move into a moonless observing window, the comet remains spread out and tailless. Because it's well past perihelion and leaving Earth in the dust, it's expected to fade this week to around magnitude +9. That makes it fringey for 50-mm binoculars but likely still visible from a dark sky.

Westward Ho!

This map shows nightly positions for comet 45P/H-M-P as it travels west from Boötes into Coma Berenices. If you’re east of that time zone, the comet will be very slightly behind the positions shown; if west, it will be slightly ahead of them. Stars shown to magnitude +8. Click to enlarge and then print out for use at the telescope.
Map: Bob King, source: Stellarium

Telescope-toting observers will do better and enjoy views of what resembles a puff of smoke or mist, with a somewhat more "condensed" or compact central region. 45P/H-M-P still has legs! Pushing ever westward from Boötes through Canes Venatici and into Leo, on February 14th, the comet covers 6° in 24 hours, 5° on February 15–16, and 4° on Feb. 16–17. When you do find it in your telescope, take a peek a little while later, and you'll notice movement to the west at the rate of about 12′ an hour.

Swing into Spring

This black and white map, which plots a longer arc, might prove more convenient for outdoor use. The comet's position is plotted nightly for 10 p.m. CST. Stars are shown to magnitude +8. North is up.
Created with Chris Marriott's SkyMap

The best time to view the comet in the coming week will be from around 10–11 p.m. local time, when it's well placed in the eastern sky. 45P/H-M-P should fade rapidly by late February, so be sure to see it while you can. At its next bright return in October 2032, the comet's expected to reach magnitude +7. I'll keep an eye on it, so check back here for an update in a day or two. Happy hunting!

** UPDATE: Great news! I was able to spot the comet in 10x50 binoculars 15 minutes before moonrise tonight (Feb. 14). It appeared quite large — about 30′ or a full moon diameter wide — but of course faint and very diffuse with an estimated magnitude of +8.3. In just a night or two, the comet will be considerably higher before moonrise and a little bit easier to see.

** UPDATE #2: The Arecibo radio dish spotted the comet too! Instead of visual observations, Arecibo captured radar images of the comet as it flew by Earth, making it the seventh comet to be imaged by radar. The image below shows 13 images collected over two hours of observation.


11 thoughts on “Comet 45P Returns to Dark Skies

  1. Graham-Wolf

    Great work, Bob.

    45p/H-M-P fever all round…. may they never find a cure. This is comet watching, as it should be. The charts are great, if indeed upside-down and back-to-front for us in the Antipodes, but “Stellarium” certainly comes to the rescue. The comet’s large green coma reminds me somewhat of C/1996B2 Hyakutake…. the 3rd closest comet to whizz past the Earth. Recall also seeing IRAS-Iraki-Alcock in 1983, but certainly wasn’t around for Lexell in 1770. This apparition of 45p may be my 6th or 7th. Having so much off a buzz, just can’t be bothered counting.

    Regards from 46 South, NZ.
    Graham W. Wolf.

    1. Bob KingBob King Post author


      Your enthusiasm is infectious! I just got in from viewing the comet in 10x50s. It’s still hanging in there around +8.3. Very large and diffuse and headed (eventually) to a sky near you!

  2. Aqua4U

    Thanks for the updates and maps! I’m still hoping to see this comet as I’ve tried several times but have been clouded or rained out so far. Am hoping for a hole in the clouds, but that looks iffy at best? We’ve been getting slammed by storm after storm here in Northern California. Then when a clear spot DID appear the full moon blew away that off.

    I’d love to see this comet in the 12X70 SkyWatcher binocs I got for x-mas! A ‘proper’ introduction? Then if the hole is big enough I’ll roll out my 12 1/2″ to get up close and personal with it! Now where did I put those weather change cards I had?

    1. Aqua4U

      Back in the early 90’s I belonged to an astronomy club at a ranch near Lake Berryessa, CA. There were usually 4-6 kids running around. Anyway, when the clouds threatened I’d line up the kids and have them all blow as hard as they could at the clouds. GO AWAY!

      Hey… don’t laugh. It worked! Go figure…

  3. Graham-Wolf

    Hi Bob.
    Your latest Mv 8.3 report noted… can’t wait to “nail” the comet again.

    Will have to wait a few more days down here at 46 South, for the Moon to rise much later, and the region near Arcturus also to rise. Comet is still too far north for us, at present. At 10:50 UT last night, stepped outside to see Last Quarter Moon about 20 deg up in the East and to the right and lower of Jupiter. My best guess for my next window for 45p, will be Feb 21st – 25th. I’ve been running more Stellarium simulations on the laptop to make sure. Great that you folk in the northern hemisphere are seeing it already. It sure helps extend that enviable data curve.

    Still impressed with your Feb 5th astropic. It’s a beaut!

    Like you, I am also a mild-tech “point and shoot astro-photographer”. Your own pic roughly equates to ~10s at 1600 ISO. I use a Canon A480 Compact, and do 10s and 15s at 35mm efl, ISO 1600, F3. I also use a 2s shutter delay, to reduce “shake”. Multiple shots taken, with appropriate Darks and Flats, then processed with “Deep Sky Stacker” just might get down to ~ Mv 10. Good luck with any further efforts, Bob.

    Regards from 46 South, NZ.
    Graham W. Wolf.

    1. Bob KingBob King Post author

      Hi Graham,

      Good luck on a sighting of the comet. Sounds like we shoot astropix similarly. What stacking program do you use and is it for Mac or PC?

  4. Capella80Capella80

    Oh well, never got to observe 45p anyways. Clouds moved in with some showers last night. Last observing session I got up early and observed from 4 to 6 in the morning, totally forgot I was waking that early to observe HMP. (It still wasn’t bad. Iridium flares, the ISS, Jupiter bands, Jovian and Saturian satellites, M13, various doubles, and speaking of satellites, I almost fell over when a satellite passed front of Alpha Vupecula.) Maybe I’ll try to get a good look of 2P/ Encke. Unlike the saying “March, in like a lion, out like a lamb”, it tends to be the opposite in Nashville. Might want to get some observing in.

    From 36° North, -Capella.

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