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Old 02-05-2013, 01:13 PM
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Default Comet Lemmon

A quick LRGB shot taken last night of the head of Comet Lemmon (C/2102 F6) currently in Octans. I think that there's just the hint of the tail leading off to the left. I read that the green colour is due to cyanogen (CN) and diatomic carbon (C2) which apparently glow green when illuminated by sunlight in the near-vacuum of space.

The comet was fairly trotting across the star field as can be seen by the length of the interrupted star trails. I had to keep pausing the video acquisition while I re-centred the comet hence the gaps in the star trails. The luminance channel took just under 2 minutes of exposure time and there are seven gaps in the white luminance trails meaning that I had to re-centre every 25 seconds or so.

Meade 12 f/10 SCT + x0.5 fr + Gstar-Ex mono
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File Type: jpg 0166 Comet Lemmon c2012 F6.jpg (273.3 KB, 28 views)
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Old 02-05-2013, 01:29 PM
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Well done David. I had a hunt around the area with my binocs. last night but was unable to spot it. Probably too small a dot in amongst a lot of other small dots.
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Old 02-05-2013, 05:57 PM
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Very nice shot, David!
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Old 02-05-2013, 07:00 PM
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Robert you should find it an easy target in your binoculars. My 7 x 50s show it very well. It is apparently at about mag 7 and shows as a fuzzy ball so you will know when you've located it. Look almost at the SCP. The attached cropped screenshot from SkyTools3 shows its current position (at 7:58 pm AEDT) and its current track (from 4th to 7th February).

David
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File Type: jpg Comet Lennon Trail.jpg (59.7 KB, 8 views)
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Old 02-05-2013, 07:23 PM
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Thanks David every mornig I awake to clouds been trying to get a shot with the 16" Dob. Its raining now so not much hope for tomorrow.
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Old 02-06-2013, 09:21 AM
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Great shot David...
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Old 02-06-2013, 10:19 AM
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Thanks David. I'll have another go tonight. If the weather stays clear (I live in high hopes) I'll have my scope out.
I have inverted (B&W) and enhanced the sky map for ease of use under red-light and also to save ink on printing.
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File Type: jpg Lemmon Path.jpg (311.0 KB, 6 views)
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Last edited by White Dwarf; 02-06-2013 at 10:32 AM.
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Old 02-06-2013, 12:03 PM
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Nice pic taken there mate. You gotta have sharp eyes and be very patient for that kind of shot.

nice work.
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Old 02-06-2013, 08:24 PM
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Good effort David.
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Old 02-07-2013, 02:55 PM
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Default Just Pretending

Out again last night seeing if I could improve on the previous image of Comet Lemmon. When back inside processing the avis my wife asked me how fast the comet was travelling. Well that stumped me. But I got to thinking that just maybe I could work it out using the image. Never done that before but seemed like fun to try. I realised that I needed to know the distance to the comet so I cheated and looked up a value of 92 million miles on the internet. Thereafter the calculation went like this :
  • Selected the prominent red filter star trail and determined its overall exposure time including pauses to re-centre the comet every so often. 300 frames @ 2.56 sec per frame x 1.3 (to allow for the pauses) = 998 sec
  • Used my sky atlas to measure the width of the camera frame 578 arc sec.
  • Measured the length of the red trail on the image (172 pixels) and the width of the image (1,165 pixels)
  • Calculated the length of the red trail across the sky (578 x 172 / 1,165) = 85.43 arc sec
  • Calculated the circumference of a circle having a radius of 92 million miles (148,100,000 km) = 930,539,743 km
  • Calculated the part of that circumference spanned by the travel distance of 85.43 arc sec (930,539,743 x 85.43 / (60 x 60 x 60) ) = 368,058 km
  • Speed = 368,058 / 998 = 369 kps
Of course that would be the apparent speed across our line of sight and it could only be increased by any radial component (caused by moving towards or away from us). But at least it was a figure. So how accurate is it? I'd be quite satisfied if it was in a ballpark one or two removed from that of the real figure. But when I did eventually find a value reported on the internet it was given as 401.3 kps. Assuming that that contains some radial component I'm quite chuffed with the end result. Can pretend (just for a day) to be a scientist!
Attached Images
File Type: jpg 0176 Comet Lemmon c2012 F6 6 Feb 2013.jpg (164.9 KB, 9 views)
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