While waiting for another comet to rise high enough to start shooting, I took a few shots of Comet Johnson even though the moonlight was strong in that area and I wasn’t expecting to get much. Surprisingly, the comet shows up with a slightly diminished tail, but the head and coma show well enough.
I did not spend much time on it and was not going to bother processing the data at first. The colors and dim areas suffered, but not enough so that it couldn’t be fixed somewhat. Lucky for me. 🙂
Terry Lovejoy’s newest comet is in outburst and has brightened quite a bit above what was expected of it. Now, it is a really nice comet in the dawn skies. Unfortunately, it is moving fast and quickly heading lower and lower to the horizon with each morning. So, the good viewing window is short and sweet.
I had to wait for it to clear a roof and it was already after 10:30 UT (5:30 am CDT,) so I had to shoot it between the start of astronomical twilight and nautical twilight. Plus, this is from a Bortle red/white zone, so I had lots of LP to contend with. Not the best conditions, but hey, at least I got a usable image.
Taken from a Bortle Red/White zone, this image is 40 sub-images of 120 seconds each at ISO 800. This is double than what I was able to do before. The inclusion of an IDAS-LPS drop-in filter for my Canon T3 allowed this one stop of extra exposure. So, now I know how much the drop-in filter blocks, which is quite a bit.
Regardless of the above, the gradients and the color shift from removing that much LP still make processing difficult and tedious. I am glad I can drive just 30 minutes and get to a spot dark enough to be camera noise limited instead of skyfog limited. It is such a joy to process images that have low LP levels. 🙂
Here’s a quickie of Comet Johnson. I took two test images before the automated run, which I ended up using. But, I was pretty tired by the time I got to this one, so I let it shoot automated while I took a nap. Unfortunately, the guiding got screwed up after only 11 sub-images and I didn’t shoot more of it after I woke up since it was near sunrise and I needed to shoot calibration data for my other stuff instead. Oh, well…
On Friday evening, March 31st (April 1st in Universal Time) I drove out to a dark sky site and got as many images of Comet 41P as I could. 41P/Tuttle-Giacobini-Kresak was closest to Earth on this day and I was hoping I could document the encounter.
I ended up with 80 good sub-images out of about 100. Unfortunately, I had guiding problems, equipment issues and mount troubles. A bad connection on my new battery pack kept me from starting until I re-rigged it and during the night the mount kept making knocking noises and jerking in RA, making lines instead of star points every 5 to 10 sub-images. I’ll have to figure that one out, since it never did that before.
At least it was very dark and transparent. I was camera noise limited and not LP limited for my exposures. It was kind of weird to shoot 7 minute subs and see that I still had a ways to go before mid-histogram. I wish it was like that every time. lol
Here’s another image of Comet 41P/Tuttle-Giacobini-Kresak taken from a Bortle red zone location which is in the middle of a larger city. No filters and a stock camera on a F/5.6, 480mm focal length telescope were used.
I was able to shoot 2 minute exposures at ISO 400 before it maxed out the light pollution (LP.) This is the StarFreeze version of the data. I have lots more data, too. There is another set of 40x120sec shots and some 90 sec, ISO 400 sub-images I did early on when the comet was lower in the sky and deeper in the LP muck.
For now, this doesn’t look too bad to my eye, considering the conditions. I would estimate the coma is twice the size we see here from a dark-sky location. I’m glad the sky was nearly transparent this night. It made processing easier.
Here’s the obligatory star streaks version:
On the night following the encounter between M108, Comet 41P and the Owl Nebula, the comet was still in the field of view of my setup, so I went back for seconds. I just couldn’t pass up the opportunity to shoot a comet conjunction again!
I went with 3 minutes sub-images at ISO 200, since the 1 minute ISO 800 subs were too cooked by the LP for my taste. Unfortunately, the sky was not as transparent as the previous night and that half-stop of underexposure was needed to get around that. The trade-off was I didn’t get as much of the comet’s coma. Oh, well.
Also, at that exposure length, the comet’s pseudo-nucleus trailed a bit, since it is moving with respect to the Earth and stars and slowly picking up speed as time goes on, to boot. It was not enough to notice if I carefully over-exposed it a bit in processing to make it fatter, luckily. Check the star streaks version, which I did not overexpose, and you can see how far the comet moved in 3 minutes:
A Televue TV-85 w/0.8x focal reducer/field flattener, a Canon T3, my laptop running EQMOD, driving my Atlas EQ-G mount and PHD2 Guiding with an Orion StarShoot guider/Orion Ultra-Mini guidescope was some of the equipment used.
It is not uncommon for comets to pass near famous Messier objects or NGC catalog objects and put on a good show. This comet encounter is special in that there are two famous objects that the comet is having a conjunction with. One is a relatively bright galaxy called M108. The other is the Owl Nebula, one of the better planetary nebulae in the skies.
I shot this with the Canon T3 and Televue TV-85 combo. I used one minute sub-images at ISO 800 and that was about max for the skies I was under. I’m sure people with darker skies got better results. However, I think being able to pull anything out of the skies at this location is great. LP was bad and I had terrible gradients to deal with in post-processing, but I managed. 🙂
I also did a quick star-streaks version that seems to show a longer tail. Not sure, since there were some dust doughnuts left over from an apparently bad batch of flats I used and I had to clone them out. These aberrations were in the tail area, so it could be some remnant of that.
Check it out:
One thing I’ve found out with using electronically assisted methods to view dim objects in bad LP conditions is this: Live stacking generally improves things, but only at first. If you want something as dim as Comet 41P to show any more than just the inner coma, you have to stack with lots more subs using more advanced stacking methods than just average and additive.
So, I shot 103 subs-images, along with 30 darks and about 30 bias images for this object. I brought them into IRIS and used only the first 60 because that is all I could get to align. The usual methods of aligning based on the drift per hour in x and y coordinates doesn’t work if the sub-images are not timestamped. This is another deficiency in the low-end capture and stacking program, RisingSky (ToupSky.) Not sure if SharpCap has the same issues.
Anyway, at least I was able to obtain a basic image and considering the conditions, it is not too bad. Compare this to my previous effort with the Aptina AR0130 sensor. This would probably work lots better at a dark sky site. But, I don’t know if I would waste time on shooting with the RT224 when I could use the Canon T3, which is more sensitive when it comes to comets and captures a much larger field of view.
I was fooling around with the Toupcam from a red/white LP zone and trying to get Comet 41P to show up. I ended up using SharpCap and doing live stacking with between 10 to 23 x 8 sec exposures for each stack. Then, I combined those stacks in IRIS and aligned them on the comet. It came out to be a total of 18 minutes worth of exposure, albeit in a heavy LP zone. So, I got it to show up, but the color and faint details of the tail and coma got lost in the noise.