I used 3,4 and 5 minutes at ISO 1600, plus 12 minutes (only3) at ISO 400. Although 5 minutes bagan to show the sky fog in the dark areas it still showed more contrast in the comet's tail. So the plan is to even go longer tonight, 6,7 and 8 minutes at ISO 1600.
I want to find what is the maximum depth I can go before sky fog over powers the tail detail.
Just a bit of rough maths from the 39-odd degrees of tail detectable on 20 Jan:
Earth was 0.984 AU from Sun, comet 'head' was 1.17 AU from Sun & 0.616 AU from Earth at the time. Using an assumption that the tail points directly away from the Sun (probably a reasonable assumption given its extreme straightness and the fact that the comet is a sungrazer), then the detectable tail length was about 1.24 AU or 185 million kilometres! It would only take an extra degree or two of tail length to become detectable over the next few days and the length would be around 200 million kilometres.
Cheers -
That's amazing Rob! Certainly puts the size of this thing into perspective!
Hi all, here is last nights image, 13 x 3 minutes with 24mm lens at F1.4 and Astro 40D at ISO 1600. I would usually use F2 for better star images but need maximum sleep time due to early starts with shearing for one more day.
Comet is getting very faint, still got a long tail, but will soon be beyond my gear to record.
Tried photoshop exposure tweeking with offset and gamma correction to help bring out the tail.
Good to see that Lester is still dragging it in there.
Where I was over the weekend conditions weren't good enough to make any solid observations, but it cleared nicely here after astro twilight was over. I dragged out my reclining meteor observing extendable chair to lay back and Hunt for Lovejoy up near the zenith with the bino's.
Transparency was 9/10 so thought I might confirm what I thought I saw briefly last night before clouds interupted things. I am happy to say that I could still detect the first 3 degrees or so. Once I found it I went back inside and made up a chart from Megastar 5, than came out and plotted what I could see.
All I can say is that it wasn't easy. Sweeping quickly across the comet at right angles with the bino's confirmed my suspicions, but there were numerous small star groupings in line with the tail that made me think the comet was longer. In the end I dismissed those groups and came up with what is on the drawing attached. It will be interesting to see how it fits with any shots taken tonight.
What a change. A month ago I was observing Lovejoy within 10 degrees of the horizon, now it is within 10 degrees of the zenith!
Top stuff again Lester, with a bit of work it appears to show the tail extending extremely faintly to above Omicron2 Canis Majoris, or about 39 degrees.
That's a good image from last night.
I can't squeeze any more out of my camera, especially in this heat.
So it will be interesting to see if you can pull a few more rabbits out of the hat.
Thanks Lester for providing an image from last night.
I hope that you don't mind but I took the liberty of cropping a piece around the head for comparison with my drawing. I have highlighted some groups of stars that I used to plot the comet that also appear on your image. Given the time difference between N.Z. and S.A. the fit is pretty good. If it stays clear I'll be doing another drawing plus have a go with the 20 inch to see if I can find the head with that.
the sky cleared here for just over an hour. This is 7x6 minute exposures with 24mm lens at F2 and Astro 40D at ISO 1600. Canopus to the bottom and Sirius to the left.
no luck last night. What appeared to be a very clear sky may have had just a trace of cirrus still present after sunset. I tried observing the comet without knowing the exact position but just a general idea so that I wouldn't be baised. That didn't work, so I went in and had a look at where it should be and came back for another go with the 10 x 50's. I had a suspicion that I saw about a degree around the head, but nothing so conclusive that I would commit to putting it on paper. After nearly an hour I packed it in. Even a slight decrease in the quality of the transparency made it impossible to distinguish the comet from the background! On that basis I didn't give the 20 inch a go, maybe it would have made a difference?
That will be my last crack at it Lovejoy as the weather is putting paid to anymore attempts for nearly a week. Lester your latest shot confirms my suspicion as well as emphasising just how faint it really is now. Great effort mate.
Hi Coops, yes any lack of sky transparency would make the comet a "no show". I was lucky last night as it was still cloudy here in the morning with a very brisk temperature after 2 hot days and evenings.
Thanks Liz. Here is tonights effort, 25th January = 13 exposures of 6 and 12 minutes with ISO 1600 and 800. Will try an individual stack of each ISO group tomorrow to see if the ISO 800 has more contrast.
For some unkown reason when I add flat frames into the stack, DSS doesn't register the bottom left area of the FOV correctly, so this image has not got any flats included.
Great stuff Lester! Seems to show the tail fairly clearly to just past Furud (Zeta Canis Majoris), or 26 degrees. After that vague hints or nothing (see attachment).
I shot it too - lot harder to get a trace than last time I tried. Shows the same thing as yours, though not as clearly (26 degrees). Also like yours, there's a hint out further but not enough to say one way or the other.
Cheers -
Last edited by Rob_K; 26-01-2012 at 01:53 AM.
Reason: Forgot attachment
