Comet 17P - Estimate of physical size

Estimate of physical size of Comet 17P:

2 arcmins = 120 arcsecs =~ dia. 142472 kilometers
3 arcmins = 180 arcsecs =~ dia. 213708 kilometers

Computations - using the sine rule

1 a.u. = 149,597,870.691 kilometers ; wikipedia
Distance Earth to Comet 17P Oct 25 = 1.637 a.u. ; NASA-JPL Near
Earth Object simulator
Distance Earth to Comet 17P Oct 25 = 244,891,714 ; Product
Comet 17P object size: 2-3 arcmin ; my obs and other internet reports

Physical diameter using the sine rule from object's diameter in
arcsecs:

Physical diameter = [ Deg2Rad( Objdiameter_arcsec / 3600#) ) *
Distance_to-Object ]

Results for 120 and 180 arcsecs:

120 arcsecs =~ 142472 kilometers
180 arcsecs =~ 213708 kilometers

Diameter of major planets ; wikipedia

Jupiter 142985 km
Saturn 120534 km

Worked example for 120 arcsecs:

Objdia/3600 = 0.0333333
Deg2Rad ( Objdia/3600 ) = 5.8173 x 10^-4 = 0.00058173
Deg2Rad ( Objdia/3600 ) * Dist_to_object = 0.00058173 x 244,891,714
Deg2Rad ( Objdia/3600 ) * Dist_to_object =~ 142,462

- C

On Fri, 26 Oct 2007 12:19:31 -0700, canopus56
wrote:

Estimate of physical size of Comet 17P:

2 arcmins = 120 arcsecs =~ dia. 142472 kilometers
3 arcmins = 180 arcsecs =~ dia. 213708 kilometers

As of last night, I put the distinct coma size at 6 arcmin, with a
diffuse coma extending to 17 arcmin. So I'd make those sizes several
times larger.

Intensity profiles from the last two nights are at
http://www.cloudbait.com/gallery/comet/holmes.html

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

On Oct 26, 2:20 pm, Chris L Peterson wrote:
As of last night, I put the distinct coma size at 6 arcmin, with a
diffuse coma extending to 17 arcmin. So I'd make those sizes several
times larger. snip

Thanks, Chris. I have created a physical size reference table for 2
to 30 arcmins based on today's distance estimate here -

http://www.utahastronomy.com/Current...e_of_Comet_17P

- Canopus56

On Fri, 26 Oct 2007 15:16:22 -0700, canopus56
wrote:

Thanks, Chris. I have created a physical size reference table for 2
to 30 arcmins based on today's distance estimate here -

http://www.utahastronomy.com/Current...e_of_Comet_17P

Good thing. Before the snow rolled in this evening, I got more images.
The coma is now well over 10 arcmin across. I've updated the profiles at
http://www.cloudbait.com/gallery/comet/holmes.html ; it is now obvious
that the nucleus has split, or that the coma is becoming significantly
offset from the nucleus (can't really say which).

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

Chris L Peterson wrote:
Good thing. Before the snow rolled in this evening, I got more images.
The coma is now well over 10 arcmin across. I've updated the profiles at
http://www.cloudbait.com/gallery/comet/holmes.html ; it is now obvious
that the nucleus has split, or that the coma is becoming significantly
offset from the nucleus (can't really say which).

I think what we are seeing may simply be a projection effect: the bright
elongated inner region may well be the tail seen extending behind the
comet (and a bit to the side). The offset in general may be due to the
approximately 15 degree viewing angle. One thing for su we don't get
the chance to see bright active comes from the point of view very often.

Clear skies,
Greg

--
Greg Crinklaw
Astronomical Software Developer
Cloudcroft, New Mexico, USA (33N, 106W, 2700m)

SkyTools: http://www.skyhound.com/cs.html
Observing: http://www.skyhound.com/sh/skyhound.html
Comets: http://comets.skyhound.com

To reply take out your eye

On Oct 26, 1:19 pm, canopus56 wrote:
snip all

In a Cloudy Night's forum, someone pointed out that you can use the
Google search box's built-in calculator to find the physical size of
Comet 17P. In general -

sin ( radians (your_arcmins arcmins) ) * 1.62900 [a.u.] * 149 597 871
= physical size 17P

Get the current day's distance to Comet 17P from the NASA-JPL Near
Earth Object orbit simulator -

http://ssd.jpl.nasa.gov/sbdb.cgi?sstr=17P&orb=1

An example of a string that is formated for use in the Google search
box is:

sin(radians * (10 arcminutes)) * 1.62900 * 149 597 871

which yields = 708 878.821 kilometers

According to Allen's Astrophysical Quantities, typical comet coma
physical diameters are 10,000 to 100,000 km.

- Canopus56