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Comet C/2009 P1 Garradd

 

This comet, discovered in 2009, has been measured (by others) to have an orbital eccentricity of 1.001011. So its orbit is hyperbolic rather than elliptical and it will not return to the Solar System.

 

 2012 Mar 19

I last photographed this back in the autumn but since then it has moved through Hercules and Draco and is now north of Ursa Major. This caused a problem setting up for the photo because the zenith can be awkward to get to with an equatorial mount. After locating the comet I noticed that the bottom of the telescope was being driven into one of the tripod legs and so I had to start again, swinging the telescope through 180 degrees about the polar axis. The result is certainly pleasing. The comet has a nice blue tail of particles being driven away by the solar wind:

Canon EOS 5D MkII ISO6400 64x32s
254mm Newtonian f=1200mm f/4.8
HEQ5 equatorial mount, driven but not guided
2012 Mar 19 00:01:37-00:39:18 UT
From Rookhope 54.8N 2.1W 330m asl. Rural, almost no light pollution (3 Bortles)

I did not track the comet directly. My equatorial mount simply did its usual thing of driving at sidereal rate (ie, star rate, compensating for the rotation of the Earth). The comet does not move perceptibly in each individual half-minute exposure. But between the first and last of the 65 exposures the motion of the comet against the stars was significant, as is evident in my image.

The key is software. I have written the stacking part of my GRIP application so that for comets and asteroids the object of interest can be held still in the stacked result.

 2011 Sep 28

Canon EOS 5D MkII ISO6400 32x30s 254mm Newtonian f/9.6 (f=2400mm, Barlow)
HEQ5 mount, driven but not guided 2011 Sep 28 21:24:27-21:43:09 UT
From Rookhope 54.8N 2.1W 330m asl. Rural, almost no light pollution (3 Bortles)

 2011 Sep 21

Canon EOS 5DMkII 254mm Newtonian @2400mm (2x Barlow) f/9.6 ISO6400 33x30s 2011-9-21 21:26:34-21:45:23UT
From Rookhope 54.8N 2.1W 330m asl. Rural, almost no light pollution (3 Bortles)

On HEQ5 mount, driven but not guided.

The 33 separate half-minute exposures of my photo have been stacked (using GRIP) so that the comet appears to remain stationary while the stars trail past. The area shown is 0.42° x 0.30°. Using GRIP again I measured the trail lengths as 0.010°. Elapsed time was 18m49s = 1129s so the comet was moving at 0.010 x 86400 / 1129 = 0.77°/day.

 2011 Sep 14

Canon EOS 5DMkII 254mm Newtonian @2400mm (2x Barlow) f/9.6 ISO6400 38x30s 2011-9-14 21:03:54-21:28:13UT
From Rookhope 54.8N 2.1W 330m asl. Rural, almost no light pollution (3 Bortles)

On HEQ5 mount, driven but not guided. I used a 2 inch (5.08 cm) 2x Barlow lens for increased magnification.

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