Update on Comet Hartley 2

Comet Hartley 2 has now reached naked eye brightness for those lucky enough to observe from a dark site. For the rest of us the comet is actually a rather difficult object. Under any level of light pollution, the comet is nearly impossible to see with just the naked eye. At my home (Lm = +5.5) the comet is a faint, barely discernible fuzzball in 10×50 binoculars. At least the comet’s location is relatively easy to find due to the large number of bright stars available for star-hopping. Still the comet has not been an impressive sight and I’d guess that most inexperienced observers will have a hard time finding it.

For example, I just went out to catch a glimpse of the comet as it passed by the Double Cluster in Perseus. I  was rather surprised that I could not find it at first. Because it was located near a few bright stars it was swamped by their glow. The proximity to the stars also ruled out any attempt at estimating its brightness. On of these nights I need to drive out to a darker site and see how much of a difference that makes.

The reason for the difficulty in seeing the comet is twofold. One, the comet is large with recent CCD images finding the comet’s light spread over a coma 36’+ across. Two, any amount of light pollution really does a number on low surface brightness objects. Since most of us live and observe near city lights, objects like Hartley 2 can literally be lost against the bright sky.

The comet is much easier to see in CCD images and I continue to observe it with the LightBuckets 0.2-m (8″) astrograph. The two images below are from the nights of Oct. 2 and 6 UT, respectively. Due to the increasingly rapid motion of the comet I was able to median combine the 19 individual images from Oct. 6 UT in such a way as to make the stars (mostly) go away. The coma is fairly circular and there is little fine detail in the coma. A narrow dust(?) tail points just west of south (PA ~200-205) and can be traced up to 12′ from the nucleus. This is still within the outer coma so this comet does not (yet at least) display the ‘lollypop’-type appearance typical of 5th to 6th magnitude comets.

Recent visual magnitude estimates place the comet between magnitudes +5.3 and +6.5. My own visual estimate from last night (Oct. 7.22 UT) gave a magnitude of +5.9. CCD derived measurements from the LightBuckets 0.2-m come in a little fainter at +6.3. The following table presents a summary of my visual and CCD observations in ICQ .

Oct. 07.22, m1= 5.9, Diam=24' (Visual, 10x50 binoculars)
     06.27, m1= 6.3, Diam=36' (0.20-m reflector + CCD + Astrodon G filter)
     04.17, m1= 6.5, Diam=16' (Visual 10x50 binoculars)
     02.43, m1= 6.7, Diam=38' (0.20-m reflector + CCD + Astrodon G filter)
     02.30, m1= 6.5, Diam=20' (Visual 10x50 binoculars)
Sep. 25.31, m1= 7.3, Diam=23' (0.20-m reflector + CCD + Astrodon G filter)
     15.28, m1= 8.2, Diam=24' (0.20-m reflector + CCD + Astrodon G filter) 
     12.23, m1= 8.1, Diam=26' (0.20-m reflector + CCD + Astrodon G filter)
     03.33, m1= 9.8, Diam=8'.6 (0.61-m reflector + CCD + Astrodon G filter)
Aug. 05.37, m1=11.9, Diam=4'.4 (0.32-m astrograph + CCD + Astrodon G filter)
June 17.41, m1=16.8, Diam=0'.6 (0.32-m astrograph + CCD + Astrodon G filter)

As the graphs below show, the brightness trend has not changed over the past month. All but a single visual estimate has fallen below the expected brightness of the comet (based on its last well observed return in 1997). So unless we are all missing a large fraction of the coma and the comet is actually brighter than is being reported, Hartley 2 is on pace to peak at magnitude +4.5 to +5.0 in two weeks.

About Carl Hergenrother
I am a professional astronomer specializing in the study of comets, asteroids and meteors. This blog will focus on my professional and amateur work in this field

6 Responses to Update on Comet Hartley 2

  1. pratik pawar says:

    Hello sir…. i want your help…we observed night sky whole night but we didnt find comet….we observed for 3 nights but no comet…… we are using 8” reflector and 32mm lens…but near double cluster there is no such thing….our view is right or not? we are observing from india city- pune… can u tell me the timings of the planet from india?? so dat we can observe once again… and i have photograph of that double cluster section using Nikon d80.. there is smthing greenish and diffused..i can sent u …ple help me.
    Regards
    Pratik Pawar
    India City-pune
    (+919325077244) PHONE NO

    • Carl Hergenrother says:

      Hi Pratik,

      Yes, Comet Hartley 2 is proving to be a very difficult object to find. Unfortunately, the comet is so big and diffuse (over one degree or 2 apparent lunar diameters across) that any amount of light pollution will make seeing the comet difficult.

      You may want to try looking for the comet in a smaller instrument like a pair of binoculars. If the comet is too magnified you can literally look right through it without noticing such a low surface brightness object.

      You can find good finder charts for the comet at Sky and Telescope. Currently the come is traveling south through Perseus and is many degrees from the Double Cluster now.
      http://www.skyandtelescope.com/observing/highlights/102632669.html

      Yes, please send me your picture at and I’ll tell you if you caught it. The comet should be a greenish fuzzball so I have no doubt that you caught it with your Nikon.

      Thanks for writing and I hope this helps,
      – Carl

  2. Debbie Dobkin says:

    My family celebrated my Dad’s 80th birthday in the NC mountains this past weekend. The home that we rented was on the outskirts of Lenoir NC and the only house on a mountain. We had an unbelievable view on the night sky. On Friday there was a new moon and we were in total darkness. Our view faced north and we could see the outline of Grandfather Mountain and lights in distance of the small town of Blowing Rock, NC. Suddenly this huge fireball with a tail came racing across the sky. It there long enough for us all to see it (approximately two to three seconds). You can imagine the hooping and hollering we all made. First we thought it was a shooting star but the tail made us think it was a comet. My brother said it had to be space trash to produce such a firey tail. Is it possible this was Comet 103P/Hartley 2 or the recently discovered comet C/2010 A4 (SIDING SPRING)?

  3. Lisa says:

    Lots of great information, Carl, thanks so much! Beautiful pictures too! I hope it clears out by tomorrow around here so I can have a look with my 6″ Astroview…..

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