Comet Holmes shocks, intrigues and awes
UPDATE; 10.28.07 - 7 am -
Here's a pencil sketch I made about 5:45 am this morning using the 8-inch LX90 and a 5 mm Hyperion eyepiece which gives about a 10' fov.

It was bigger and maybe brighter and certainly more interesting. There was a stellar like nucleus, fan-shaped coma, then a much larger, fainter outer coma. I had noted heavy irregularities the night before, but I think this was because of dew on my scope.
Size - it came close to filling the 3.5mm on my 8-inch - the one with a 7-minute fov - so I would say it has to be five minutes - maybe a tad larger. Spaceweather.com has a neat animation today that shows how the comet grew over the past several days and compares it with Jupiter if we were seeing Jupiter at this distance. There are no numbers, but my own crude calculations puts the size at about 130,000 miles which I think is in the same ballpark as the animatin shows. (Jupiter is close to 90,000 miles in diameter.) Really amazing how far a little dust can go - and how fast! Think of seeing dust motes in sunlight streaming through a window and you have an idea of what you're seeing when you look at the comet. The dust motes in this case look much closer together simply because they are so far away - about 150 million miles from us.
Brightness. When I first saw it naked eye I thought I was looking at Delta Persei. I checked to the left, no comet. It took a while before I realised delta Persei at 3.0 was significantly fainter and to the right. Not nearly as bright as Mirfak (1.8) though. So I would say 2.5.
It takes high power well and the nucleus, plus at least one close star, makes focusing pretty easy. While high power gave me confidence I was seeing all I could see, I liked it better at around 150X - 200X.
There's a picture - I'm not sure who took it - here that best captures my visual experience of the comet - especially the darker area between the inner coma and the outer coma.
--- end update ---
from Dr. P. Clay Sherrod, an observer with far more comet experience than I have. His measurements from a CCD are in line, I believe with the smaller - but still large - 5 minutes of arc I estimated visually. I would expect the CCD to see more. here's what he just posted to a major comet discussion list.
UPDATE: October 28The comet has increased dramatically in size and complexity; (see LAST image on
this
page) details are:
NEW image is posted at:
http://www.arksky.org/smf/index.php?topic=1429.msg6902#msg6902
Coma diameter, overall: 348.3" (average 8 measurements, CCD)
Coma inner core (bright) diameter: 117.3"
Dark "compression/shock" ring in outer coma: 204.2"
Nuclear magnitude - 9.8 (average)
Total magnitude = 2.3NOTE that even though the comet is considerably larger on this morning than on
the
previous morning, the brightness overall has dropped (naked eye estimate
utilizing Alpha
Perseii and Alpha Cassiopeia).The last picture in this sequence below demonstrates the strong outgassing from
the
central nucleus and the incredibly rich yellow color of this comet.Clay
http://www.arksky.org/
"Omigod. Through thin clouds lit by the full Moon I had to guess where Perseus was, but I swept around with 10x50 binoculars, and wham, there was the comet!" Alan MacRobert, Sky and Telescope
From Iran to Westport to just about any where in the norther hemosphere, obsevers are being left in awe by Comet Holmes which suddenly blossomed, growing in brightness a million fold from a ghostly whisp to an easy, naked-eye object, visible even in a sky washed out by the full moon. A sampling:
"Comet 17P/Holmes stunned comet watchers across planet Earth . . ." Astronmy Picture of the Day web site.
"I was stunned at how lovely and intriguing this object was." George N. Huftalen, Jr., ASSNE member.
"This is really exciting. God, I love this hobby!!!"- Bob Magnuson, ASSNE member, in email before he even got a look at Comet Holmes.
My wife, Bren, had the best description I've heard so far. "It looks like a shuttlecock coming right at you," she said. And it does, right down to a hint of feathers. Of course, that's in a telescope. To the naked eye it looks like a star. Even the smallest binoculars, however, will show you that the "star" is something else. It's larger and fuzzier than the other stars. And in a telescope it looks like a planetary nebula. Here are two pastel skecthes I made using an 8-inch telescope at 63X. The first was made last night, the second this morning.
Note: No attempt was made to draw these to the same scale, though I think the comet was a tad larger in the morning, the change wasn't as dramatic as these drawings may imply.
Using the naked eye and 8x42 binoculars I judged the comet was about magnitude 2.6. I compared it with Mirfak (1.8) and Delta Persei (3.0) I made no direct measurement of its size, but my informed guess puts it at 3 arc minutes this morning. This is significantly larger than I've seen reported by others, so either my methord is off, or the comet has grown. What I did was look at it in a 3.5mm Hyperion eyepiece which is supposed to have a true field of view on this scope of about 7 minutes. The comet filled nearly half the field of view. I felt the nucleus was about one-fifth, to one-fourth the size of the coma and about twice as bright.
I could not make out any significant detail at any power, though the comet seemed to take magnification well. What I did note was that the nucleus was off center and it seemed a little more off center this morning than it did last night. Also, the coma has a ragged edge, though at low power it looks smooth. The coma appeared weaker towards the edge opposite what I assume is - or will be - the tail. I couldn't escape the suggestion of a shuttlecock - and a strange sense of concentric rings.
Is this comet actually coming towards us? I have not seen details on its position. It would be interesting if we're between it and the Sun. If that's the case, than we're looking down the barrel, so to speak.
When you know what you're looking at - when you have some idea just how extraordinary this event is - then you have that wonderful experience I can only describe as rapt in awe. I felt it this morning as I looked again at the comet. This time it was high in the northwest. After observing and drawing for about 45 minutes, I climbed the small ladder so I could look out the slit in the observatory dome at the whole sky. What a feeling! It was perhaps 6:05 am. In the northwest the largest and brightest full moon of the year was shining back towards me. In the southeast it was met by a dueling beam coming from brilliant Venus. Directly overhead was ruddy Mars, a cosmic volleyball that is currently dancing the epicycle fandango in the irregular ring made by the Winter Hexagon - that ring of some of our brightest stars that makes people think our winter skies must be clearer. Inside the ring was the huge, red star, Betelgeuse, a fitting companion to Mars.
Capella - yellow like the comet and forming one of the Hexagon's corners - provided a guide to Comet Holmes. You could draw a line from it to Mirfak and find Homes on it, perhaps three-quarters of the way to Mirfak. Actually, in color Holmes reminded me of Saturn which was also in the southeast, though way outshined by Venus. There was a hint of Sun in the East as we all rolled that way and you could trace that softlight up through Venus. Keep going through Saturn, Mars and over to the Moon and you've formed a huge arch that marks well the plane of our Solar System. Comet Holmes was closer to another plane - the plane of our Milky Way Galaxy.
When all these things are familiar to you - when you have a sense of place, a sense of time and a sense of perspective that you can only gain through a familiarity with the night sky - them moments like these stretch into eternity. And here we are, intelligent (we think) little bipeds on this terrific little planet and what are we doing? My only answer is we are the universe becoming aware of itself. And if you have experienced something of that, then you know why a veteran science writer, such as Alan MacRobert, starts his report on first sighting Comet Holmes with the single word: "Omigod."
Posted by Greg Stone at October 26, 2007 08:40 AM Comments? Please email me: gstone@umassd.edu