photonovore
Moonatic
Reged: 12/24/04
Posts: 2472
Loc: tacoma wa
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Holmes is currently both moving away from Earth *and* getting closer to Earth! This is because although the comet is in the portion of its orbit where it is headed away from Earth, the Earth's orbit is currently carrying us in the same direction at a slightly higher relative velocity--we will be "catching up" to the comet until Nov. 6th at which time the comet's relative velocity will cease to be offset by our own.
Here is a orbital diagram whih may be of interest:
JPL Orbital generator
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Mardi
4" achromat, ETX-70.
Whitepeak Lunar Observatory Website
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photonovore
Moonatic
Reged: 12/24/04
Posts: 2472
Loc: tacoma wa
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Jeremy, I have my doubts that the annular appearance of the nebulous cloud of this comet is an artifact of either our visual system or of image processing. The best image i can find illustrating the detail of this entire structure is from a new participant here at CN, Anton from Moscow: low contrast detail of Holmes. Rgradient was used in Iris, a technique recognized for realizing cometary detail (Christian Buil, France). Considering that the nebular area is almost certainly spherical in three dimensional shape, one would expect the outer areas to have a higher net material density (and thus reflective brightness) than the inner areas in crossection when viewed two dimensionally--as in our view from here on Earth. A spherical nebular form would be consistent with the nebular area's theoretical formation ("A flurry of sublimation would ensue with mega-jets of dusty gas emerging from the sinkhole to create a cloud around the comet..."--Spaceweather on Holmes, NASA) Considering that the cometary nucleus is doubtless also a tumbling body in space, such jets would therefore tend to distribute the material into a roughly spherical shape during the course of their eruption. The "shell" characteristic would occur as a result of the finite-in-time nature of the gas/material jet activity. IOW when the source of the debris material ends its eruptive phase, the expansion of the material already ejected would of course continue, resulting in a "shell" of debris, which eventually dissipates--as we are seeing.
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Mardi
4" achromat, ETX-70.
Whitepeak Lunar Observatory Website
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Tom Polakis
professor emeritus
Reged: 12/20/04
Posts: 551
Loc: Tempe, Arizona
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Quote:
Jeremy, I have my doubts that the annular appearance of the nebulous cloud of this comet is an artifact of either our visual system or of image processing. The best image i can find illustrating the detail of this entire structure is from a new participant here at CN, Anton from Moscow: low contrast detail of Holmes.
Mardi,
I think your explanation as to why one would expect the perimeter to be brighter makes sense, but the (unprocessed) pixels don't lie! I'm attaching a brightness profile for a horizontal slice that cuts through the image you cited. Note that there is only a plateau, if that, and certainly no reduction in brightness anywhere moving inward.
It's a powerful illusion!
Tom
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Tom Polakis
Tempe, AZ
Visual observing, DSLR photography, lunar & planetary imaging
http://www.pbase.com/polakis/
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Tuugii
professor emeritus
Reged: 03/22/07
Posts: 522
Loc: Ulaanbaatar, Mongolia
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nice works!
here is an image processed from the datas collected yesterday through 21":
I am not sure, but when I examine the image carefully, I see two dim jets going out in opposite directions from the nuclei.... do guys see/observed that?
Indeed the comet had dimmed a lot, the outer shell is no more bright and contrasty.
Tuugii
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telescope=time machine...
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Ziggy943
scholastic sledgehammer
Reged: 08/11/06
Posts: 827
Loc: SLC, UT
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Quote:
I think the tail is facing away from us (approximately) as the comet heads outwards, away from the Sun.
It looks to me that there is enough of a triangle, Earth-Comet-Sun that there should be a tail. I would expect a tail a million or more miles long to be easily visible. I think there is another explanation.
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Siegfried
4" Mak
160mm F8 TEC (born 1-18-2007, 27 lbs, 45.5" long), on AP900
150mm F17.5 (D&G lens) (first light 6-7-2008)
9" F/14.8 Alvan Clark (1915), on Byers 812
14.25 F/5.5 Newt in a roll off observatory
Others, that have come and gone
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rusirius6278
Carpal Tunnel
Reged: 11/03/06
Posts: 1722
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Quote:
Quote:
I think the tail is facing away from us (approximately) as the comet heads outwards, away from the Sun.
It looks to me that there is enough of a triangle, Earth-Comet-Sun that there should be a tail. I would expect a tail a million or more miles long to be easily visible. I think there is another explanation.
you`re right...the present tail is invisible to our eyes as explained here.
http://www.space.com/scienceastronomy/071029-comet-holmes-tail.html
Jim
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current scopes
Vixen ED103SWT
Vixen ED102S
C-102AZ/HD
StarMax 127
Jason 60/11.7
UO HD Abbe Orthos - 5mm, 6mm, 7mm, 9mm
Older UO Ortho - 4mm
Celestron 2x Ultima Barlow
and many other scopes i`ve been fortunate enough to check out...
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photonovore
Moonatic
Reged: 12/24/04
Posts: 2472
Loc: tacoma wa
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Quote:
Quote:
Jeremy, I have my doubts that the annular appearance of the nebulous cloud of this comet is an artifact of either our visual system or of image processing. The best image i can find illustrating the detail of this entire structure is from a new participant here at CN, Anton from Moscow: low contrast detail of Holmes.
Mardi,
I think your explanation as to why one would expect the perimeter to be brighter makes sense, but the (unprocessed) pixels don't lie! I'm attaching a brightness profile for a horizontal slice that cuts through the image you cited. Note that there is only a plateau, if that, and certainly no reduction in brightness anywhere moving inward.
It's a powerful illusion!
Tom
There is no argument that the raw images do not show this. However, raw images often fail to show the 'whole picture'-- which is why they are processed.
Here is an example: Comet Holmes Oct 29th, Lorenzo Comolli with an example of the detail gained through application of the Larson-Sekanina algorithm. This is a similar algorithm (rotational gradient) to that used by Anton (Iris rgradient) in the previous image reference i posted. These are considered legitimate algorithms for detail enhancement of internal cometary structures--at least by the European Southern observatory (Unique Observations Of Comet McNaught Reveal Sprinkling Nucleus See photo caption)
Based on the above (as well as the best assumptions concerning the mechanisms of formation of the nebular structure), i have to conclude that the structures indicated in these processed images, including the (two-dimensional) annulus, would be more likely to reflect actual structures than to be primarily illusory or processing artifacts. Of course likelihood is not the same as certainty... 
As an aside, you have to admit that it is also kind of neat that a processing algorithm-- developed by amateur astronomers-- has been adopted and put to use by the professional community. That is what i call "contributing to science"!
It will be interesting to see what sort of images the pros release in the next few weeks! Perhaps that will help settle this question?  Thanks for the response!
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Mardi
4" achromat, ETX-70.
Whitepeak Lunar Observatory Website
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Jeff Young
Post Laureate
Reged: 08/04/05
Posts: 3169
Loc: Ireland
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Here's a sketch from earlier tonight. I did this one at nautical twilight before the moon rose in the hopes of catching the outer halo, which was fairly easy averted vision. This is through 18x70's.
(I also inverted this image as it seems to bring out faint detail better -- at least on an LCD monitor. Let me know what you think.)
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Nikon 18x70s / UA Millennium Colorado:
Solarscope SF70 / TV Pronto / AP400QMD Coronado SolarMax40 DS / Bogen 055+3130
APM MC1610 / Tak FC-100 / AP1200GTO Tak Mewlon 250 / AP600EGTO
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Glassthrower
Vendor - Galactic Stone & Ironworks
Reged: 04/07/05
Posts: 14687
Loc: Hurricane Alley
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Nice sketch Jeff! That big Nikon was made just for this - to gobble up comets!
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Michael Gilmer - Member of the Meteoritical Society & Collector of Falling Stars.
Galactic Stone & Ironworks - Buy/Sell/Trade Meteorites, Moon Rocks, Mars Rocks, & 35 different falls and types!
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Chopin
Canis Insanus
Reged: 02/03/05
Posts: 3379
Loc: In the doghouse.
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Quote:
Nice sketch Jeff! That big Nikon was made just for this - to gobble up comets!
Agreed, that's a honey of a bino! Sweet sketch too, Jeff. 
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Jason®
Phlog
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Chopin
Canis Insanus
Reged: 02/03/05
Posts: 3379
Loc: In the doghouse.
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I just got to work, and took a gander at Holmes on the way across the parking lot. SHYKEES! Is it just me, or is it still getting bigger!?! The nebulous appearance was blatent, more so than the past couple of days, IMO. Good thing I brought my 15x85 "Comet Glasses" to work with me... 
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Jason®
Phlog
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Olivier Biot
Amused
Reged: 04/25/05
Posts: 14334
Loc: 51°N (Belgium)
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Got to see it at last today for the very first time, through some sucker holes
The color is definitely yellow, particularly at low power. What also struck me is the double halo slightly off center with respect to the nucleus. And it's big!
I can see the comet as a very slightly hazy star with the unaided eye, it's very obvious in my 15x70 binoculars and spectacular in my 80mm refractor with the 40mm Paragon or the 14mm UWA4000.
Of course I am quite lucky to have it close to the zenit as seen from my observing spot in Brussels.
Glad to have seen it at last 
Cheers!
Olivier
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Tal-200K (#199) with JMI NGF-Mini2M focuser on GEM3 • Astro-Tech AT80ED on Orion Sirius EQ-G with EQDIR & home made wireless EQDIRECT • Celestron Regal LX 8x42 & 10x42 • Helios 15x70
ATM 14" f/5 (designing mirror cell and filter wheel/focuser) • ATM 10" f/6 Portable Truss (polishing) • ATM 10" f/25 Dall-Kirkham (primary: polishing, secondary: #120 grit)
AstroForecast
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PRESTON
super member
Reged: 10/28/04
Posts: 147
Loc: Haldimand, Ontario, Canada
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Is is just me, or has this comet faded quite a bit in the last 24 hrs? Compared to last night, it seems to me the comet is quite a bit fainter tonight. My sky conditions were not great tonight, so I could be wrong.
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15x70 Binocular & Tripod
114/900 EQ Newtonian
150/1200 Dob Newtonian
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Refractor6
Post Laureate
Reged: 10/20/04
Posts: 3144
Loc: Vancouver B.C. , Canada
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It may appear fainter that's hard to estimate at this point but it has expanded noticably in size from my Friday night observations of it. Been tracking it right after sunset so it may brighten up when the sky is truly dark later. One thing I just noticed is it appears more like a glob like M92 would appear in my 50mm finder to the naked eye now and less "star" like in appearence like last Friday night. Amazing site again indeed!.
127 f/6.45 refractor Meade SWA 28mm ep at 29 power
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Stan
Takahashi FS-102 NSV
Antares 152 f/8 prototype
Antares 152 f/6.5
Antares 127 f/6.45 prototype
Orion 9x63 mini giants
Pentax 20x60 PCF WP
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Mike K
sage
Reged: 04/01/07
Posts: 464
Loc: Central Texas
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Quote:
Is is just me, or has this comet faded quite a bit in the last 24 hrs?
I don't think it has faded appreciably overall, but it is certainly expanding in size, so the brightness per unit of area may be diminished slightly. It is difficult to tell visually after 24 hours. Perhaps someone can provide CCD evidence one way or another.
I spent almost an hour observing it tonight, looking in particular for any annular structure in the coma, as discused earlier in this thread. It is interesting how changing the amount of magnification varies this effect. I am convinced it is an illusion caused by the brightness of the inner coma/fan and the high contrast edge of the outer coma against the dark sky. I subjected it to very high magnification by placing my 7mm Nagler in a 2.5 Powermate so the comet filled the entire FOV, then placed the comet outside the field and let it drift slowly in. I watched very closely many times to see if the nebular glow increased evenly or if it increased/decreased/increased. I am quite certain it does not darken inside the boundary of the outer coma.
The effect of softening on the trailing (SW) edge seems even more pronounced tonight that last, while the NE edge shows good contrast. I can easily imagine the comet's motion through space.
Based on the posts about a tail being visible in infra-red, I tried my I3 this evening with a near IR filter. The view was quite imilar to the visual image through glass, though somewhat brighter. I did not notice any structure extending out past the coma that is visible in a normal EP. I did almost think I could see motion in the nucleus, but I am sure that was due to scintillation in the I3, rather than a real effect. Out of curiosity, I put an Ha filter in the I3 and was surprised that the comet was still easily visible, though much dimmer than unfiltered or NIR.
This has been a great week observing a fascinating object.
Clear skies,
Mike K.
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Clear skies,
Mike K.
30°31" N 97°44" W, LP: Red
Observe: Once or twice a week back yard, once a month under dark skies
Favorites: Globulars, planets, face-on spirals
Equipment: CPC925/XT10i/TMB-92SS/Lunt LS60THaDS
Eyepieces: Naglers, Ethoi, UO HDs, Hyperion Zoom
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Old Dinosaur
scholastic sledgehammer
Reged: 05/08/07
Posts: 839
Loc: Out in the sagebrush
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The moon hasn't risen here yet and I have very dark and steady sky conditions tonight. The first thing I noticed was a faint halo all around what has been the outer coma. very striking and at least twice the diameter of the coma. In the inner core, now that the comet has moved there is just one point of light which must be the nucleus. This glow of a halo about blew me away, I hope some others see it and it's not just me hallucinating on bad hot chocolate!
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WRS Observatory
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Phillip Creed
Idiot Seeking Village
Reged: 07/25/06
Posts: 1033
Loc: NE Ohio
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I was talking to Dave Miller earlier tonight and was kind of torn between going to a decent spot to take advantage of the moonless window and not going. In the end, I figured I had to give it at least one shot from a dark sky, so I drove to Zepernick Wildlife Area, about 20 aerial miles east of Canton.
Here's the short version of tonight's report:
Big. B-I-G comet. Drive to dark skies and see it. Peace. Out. (for all those Jim Rome fans out there...)
Long version:
Oct 30.05 UT: m1 = 2.6, DC = 8, Dia = 8'...NE...Phillip J. Creed (New Alexander, OH) [First moonless viewing of the comet in the 25x100s. Words won't do it justice, but I'm an idiot, so I'll foolishly try. Sky NLM ~ 6.3, with occasional patches of cirrus.
The comet's continuous expansion, along with the now-moonless evening skies, made for an easily-visible outer coma of enormous size. In the 25x100s, the bright, inner coma now spans ~9', but the outer coma is now about 20' in diameter!
The "shadow arc" centered on the northeastern side for some reason didn't seem as prominent as it was the past two nights, but the bright SW-pointing fan emanating from the nucleus stood out better...hmmmm. The lack of definition between the inner and outer coma on the SW side that was noted last night was still visible.
The SW side of the outer coma had a curious visual feature; the tenuous glow seemed to stop abruptly around an 8th-mag star. I'm wondering if the star's brightness was enough to disrupt my averted vision (these binos can easily see stars past mag-12.0 from a sky like this) or if there's a little asymmetry with the coma. Based on previous photos, I'd assume it's my eyes playing a trick on me; but does anyone else notice this at at low-power in rich-field telescopes?]
Clear Skies,
Phil
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"Why suffer from insanity when you can revel in it?"
Wilderness Center Astronomy Club member since 1995
ICQ Comet Observer Code: CRE01
*****
16" f/4.5 Truss Dobsonian (FOR SALE!!)
Orion 120mm ST Refractor
23mm Axiom LX
13mm Nagler Type 6
9mm Nagler Type 6
1.75X Siebert Barlow
*****
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Refractor6
Post Laureate
Reged: 10/20/04
Posts: 3144
Loc: Vancouver B.C. , Canada
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Yes one very tiny central point of light observed and yes the glow of the halo is amazing now that the sky is dark. Simply stunning!.
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Stan
Takahasi FS-102 NSV
Antares 152 f/8 prototype
Antares 152 f/6.5
Antares 127 f/6.45 prototype
Orion 9x63 mini giants
Pentax 20x60 PCF WP
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DarrellW
newbie
Reged: 12/26/06
Posts: 4
Loc: Eastern TN
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Quote:
The SW side of the outer coma had a curious visual feature; the tenuous glow seemed to stop abruptly around an 8th-mag star. I'm wondering if the star's brightness was enough to disrupt my averted vision (these binos can easily see stars past mag-12.0 from a sky like this) or if there's a little asymmetry with the coma. Based on previous photos, I'd assume it's my eyes playing a trick on me; but does anyone else notice this at at low-power in rich-field telescopes?]
Clear Skies,
Phil
I noticed it looked a little "lopsided" tonight myself, viewing thru my Starmax 127 scope at 48x 62x, but at 123x and 205x it looked round again. This is the first night I've been able to observe with anything other than binocs so I'm not in a position to compare tonights observations with previous nights. It's definitely a spectacular view at low powers though. I did notice it still appears a very faint yellow color thru the finderscope, but even at 48x it's appears white.
Darrell
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Dipole
sage
Reged: 12/21/06
Posts: 398
Loc: Right behind you
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I finally had clear enough skies so I hauled the scope out to a darkish site and... WOW!
All your talk and the great images were a great lead in to a spectacular view! Even through the finder it was pretty impressive.
Ain't the Universe amazing?
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