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Old 10-11-2010, 03:23 PM
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Comet Observations 2nd 8th November 2010

Comet Observations 2nd 8th November 2010


10P/ Tempel 2

2010 Nov 02.45 UT; m1= 10.0; Dia= 7.7; DC= 3; 25cm L, f:5 (x39)
Coma diffuse, elongated to NW, background star in coma.
Comp Star= TYC 5851-321-1; Method= S; Cat= TJ

2010 Nov 08.44 UT; m1= 12.2; Dia= 5.5; DC= 2/3; 25cm L, f:5 (x39)
Coma large, gradual concentration to centre, not condensed.
Comp Star= GSC-5851-1163; Method= S; Cat= HS


65P/ Gunn

2010 Nov 08.43 UT; m1= 14.7; Dia= 0.5; DC= 2; 25cm L, f:5 (x83)
No tail, dim with small central condensation visible using averted vision in good seeing.
Comp Star= GSC-6932-0121; Method= S; Cat= HS


C/2009 P1 Garradd

2010 Nov 08.46 UT; m1= 13.6; Dia= 1; DC= 5/6; 25cm L, f:5 (x83)
No tail, small star-like central condensation, uniformly diffuse outer coma.
Comp Star= GSC-7492-0890; Method= S; Cat= HS


103P/ Hartley 2

2010 Nov 02.70 UT; m1= 5.6; Dia= 20; DC= 3; 7x50 B
Coma appears elongated to the East and West slightly. Not visible naked eye, central condensation gradually intensifies to centre.
Comp Star= TYC 759-2861-1; Method= S; Cat= TJ

2010 Nov 08.64 UT; m1= 6.2; Dia= 20; DC= 3/4; 7x50 B
Coma large and diffuse, broad fan shaped, elongated to the North, central condensation not stellar but bright and gradual. Faint outer coma visible using averted vision.
Comp Star= TYC 4822-3681-1; Method= S; Cat= TJ


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Old 12-11-2010, 08:37 AM
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Thankyou OBMY.
Still a few lurking out there, have tried for Tempel over the last 2 weeks, but no luck there.
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Old 12-11-2010, 08:56 AM
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G'Day Liz and OBMY;

Re: Hartley 2 Obs

Interesting that OBMY's observation notes mentions that the coma is 'large and diffuse'.

I'm trying to figure out why they couldn't detect the (only recently announced) CO2 jets emanating from its dark side, prior to the flyby by Deep Impact.

Apparently, CO2 in the jets isn't detectable remotely by either our space bound scopes or ground based scopes. (Which is one reason justifying the probe's flyby).

Would've thought that if the coma was big, there'd be enough background light and hence we'd be able to pick up enough of the absorption spectrum to detect CO2 from Earth/orbit.

Big mystery this one. (We've been wrangling on the Science forum about it since yesterday).

Any thoughts/comments/ideas ?

Cheers
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Old 15-11-2010, 08:49 AM
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G'Day Liz and OBMY;

Re: Hartley 2 Obs

Interesting that OBMY's observation notes mentions that the coma is 'large and diffuse'.

I'm trying to figure out why they couldn't detect the (only recently announced) CO2 jets emanating from its dark side, prior to the flyby by Deep Impact.

Apparently, CO2 in the jets isn't detectable remotely by either our space bound scopes or ground based scopes. (Which is one reason justifying the probe's flyby).

Would've thought that if the coma was big, there'd be enough background light and hence we'd be able to pick up enough of the absorption spectrum to detect CO2 from Earth/orbit.

Big mystery this one. (We've been wrangling on the Science forum about it since yesterday).

Any thoughts/comments/ideas ?

Cheers
Hi Craig,

There's a few factors as to why we can't see the nucleus.
As you know comets are only visible due to either scattering of reflected sunlight from dust particles or flourescence from ionised gas.
The coma is split up into 3 main parts, the hydrogen envelope which is invisible at visual wavelengths, the outer coma (which is the part i measure) and the inner coma which is what we refer to as the central condensation or "false" nucleus. The nucleus is hidden within this central condensation. Ground based telescopes are able to image the inner coma and using a special computer program, the Larson-Sekanina filter (which was produced to study coma morphology), they can carefully produce maps of jets emanating from the nucleus which are projected into the coma.

http://users.libero.it/mnico/comets/ls.htm

A similar thing was done here:
http://www.mpg.de/english/illustrationsDocumentation/documentation/pressReleases/2010/pressRelease20100426/

So we know the jets are there but what constitutes the jets will be unknown until spectroscopic observations from in-situ spacecraft can do that for us. We can't really see them as the reflected sunlight from dust particles coming from the nucleus itself creates the false nucleus which shrouds the true nucleus from observation.

My observations describing "large and diffuse" means that through binoculars or the eyepiece the outer coma has a large angular diameter comparable with something such as the moon, i view many fainter comets with coma's between 0.5' to 5', so in regards to 103P it has a coma dia of around 20' which is larger than "normal".

Hope this helps.
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Old 15-11-2010, 09:54 AM
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Originally Posted by Outbackmanyep View Post
Hi Craig,

There's a few factors as to why we can't see the nucleus.
As you know comets are only visible due to either scattering of reflected sunlight from dust particles or flourescence from ionised gas.
The coma is split up into 3 main parts, the hydrogen envelope which is invisible at visual wavelengths, the outer coma (which is the part i measure) and the inner coma which is what we refer to as the central condensation or "false" nucleus. The nucleus is hidden within this central condensation. Ground based telescopes are able to image the inner coma and using a special computer program, the Larson-Sekanina filter (which was produced to study coma morphology), they can carefully produce maps of jets emanating from the nucleus which are projected into the coma.

http://users.libero.it/mnico/comets/ls.htm

A similar thing was done here:
http://www.mpg.de/english/illustrationsDocumentation/documentation/pressReleases/2010/pressRelease20100426/

So we know the jets are there but what constitutes the jets will be unknown until spectroscopic observations from in-situ spacecraft can do that for us. We can't really see them as the reflected sunlight from dust particles coming from the nucleus itself creates the false nucleus which shrouds the true nucleus from observation.

My observations describing "large and diffuse" means that through binoculars or the eyepiece the outer coma has a large angular diameter comparable with something such as the moon, i view many fainter comets with coma's between 0.5' to 5', so in regards to 103P it has a coma dia of around 20' which is larger than "normal".

Hope this helps.
Hi OBMYp;

Thanks for your considered words .. and the links.
I've have read so many papers over the last 3 days or so that I think my eyes are about to drop out !

From what I've read, there's quite a bit involved in the issue of remote detection of CO2 from a distant comet. It seems that the Keck scopes are regarded as having some of the best IR sensing capabilites of Earth bound scopes at the moment - in the 0.8 to 5.4 micrometre band, however, these are mainly set up for exoplanet observations (perhaps not dust emitting comets). The distance to the comet and the resolving power of the scopes is one issue, as getting visibility close to the nucleus surface is tricky - even perhaps, not possible.

Deep Impact/EPOXI detected CO2 at about 4.25 microns, directly emitted at the surface source of the jets.

The space bound scopes are set up to detect at smaller IR wavelengths than Hartley's jets have proven to be. (Eg: The Hubble/NICMOS spectrometer operates at about 1.5 to 2.5 microns).

As you say, with comets, the dust causes unique issues amongst which is polarisation of the light in different parts of the absorption/emission spectra. This causes all sorts of problems for which they've developed corrective measures which in turn, rely on theoretical models. (As distinct from direct observation/measurements). As the gas moves away from the nucleus, it may also get zapped by UV etc (depending on its distance from the Sun), which may cause different atomic oscillation modes, and chemical recombination with accompanying H2O, which can then disguise the initial plain old CO2 gas signatures. Remote scopes may miss the CO2 gas because they may not be able to resolve the light close to the nucleus.

I've also found out that there's controversy about IR measurements for exoplanets as well (mainly due to the different interpretations upon which the theoretical models are based, and in evolving IR sensing technologies themselves.

Putting all this together, I can now see why they've sent up the comet probes. It removes any ambiguities because of theoretical/corrective measures and allows the creation of a comet detecting specialised set of instrumentation, which has now proven itself !!

Great stuff .. very exciting.

Apologies for hijacking your observation report .. I tapped into it to gain more knowledge of it all - thanks kindly for that .. I really appreciate the efforts you guys/gals go to, and I just wanted to let you know that others do look at your reports ... and the efforts you contribute do help others in their respective quests !!

Cheers & Regards
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Old 15-11-2010, 10:35 AM
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Hi Craig,
No worries, anytime, i want to learn more myself and it's great to see that comets do create interest among the masses. It's one of many areas which amateurs contribute and it's good to see such open and warrented discussion, no matter how way out some "theories" seem.

Keep asking questions by all means!

Cheers!
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