- LDN-1251_Siril_StarTools_NEAT.jpg (50.33 KiB) Viewed 1575 times
Atik 314E Cooled CCD
Luminance: 237x90s bin3
Total Integration Time: 5.9 hours
Bortle 5 (on my good days)
Processing: Siril, StarTools, NEAT
Each morning I make the acquaintance with the latest NASA APOD seen here:
https://apod.nasa.gov/apod/astropix.html
A couple months ago the following image was selected as Astronomy Picture of the Day:
https://www.astrobin.com/lg85ah/?nc=user
I've always loved Dark Nebulae and especially their "smokey" appearance. When I drilled down into the image details I was shocked to see that he rated his skies at Bortle 5. I'm Bortle 5 but I had no luck with the one dark nebula I tried last year. Now I understand why. The key to capturing these elusive nebulae are dark skies. That's pretty obvious given their low surface brightness. What I learned these past couple nights answered how it is possible:
#1. Allow the object to reach its highest altitude above your horizon. The sky is more transparent there. At my latitude LDN 1251 reaches a maximum altitude of 55 degrees above the horizon. On the east side of the meridian I have to wait for the object to clear trees but even then it only gives me 2 hours of imaging time. On the west side of the meridian I can follow it down quite low but I had to quit after 3 hours due to the decreased transparency when the altitude fell below 40 degrees.
#2. Your Bortle class is measured at or near the zenith (i.e. directly overhead). You can see this difference when you look overhead and see the Milky Way but as you scan down towards your horizon your sky turns gray where you can clearly see the outline of trees. So I repeat, wait for the object to climb in altitude. You can begin imaging sooner but just know that you will need to significantly increase your total integration time.
#3. Match your latitude to the declination of the object. Like I said LDN 1251 reached a maximum altitude of 55 degrees as it crossed the meridian. The gentleman who captured the APOD of LDN 1251 lives in the State of Maine which is 3 degrees farther north than me. Last year I tried imaging a dark nebula just north of Aldebaran in Taurus. In my backyard Taurus is blocked by trees as it nears the meridian so I was only able to image it when it was about 40 degrees above the horizon. That's not high enough.
Now for some comments about my image. First off, it is monochrome, not color like the APOD. Secondly, the image size is small. That is entirely due to my choice of using bin3 together with some image rotation after the meridian flip. I chose bin3 in order to turn my little refractor into a light bucket. I wasn't so much interested in creating a beautiful image as much as I wanted to prove that I could capture it. Tonight, I'll get another clear night so I might choose to switch to bin2. That will yield a better quality image but at the expense of longer integration time. Just off the top of my head it will double the time from 6 hours (at bin3) to approximately 12 hours (at bin2).
When you compare my image to his, please know that my field of view is narrower. That big bright red star in his image is just above the top of my frame. I wanted to keep it out because it is a real blow torch at 6th magnitude. In my image the bright star just below the top of the frame and left of center is the "eye of the fish" in his image.
My image is just starting to capture some of the filament structure in the smokey parts of the nebula but I would need more integration time to truly pull it out. Finally, I was hoping to pick up the "bow wave" as seen in his image but I just didn't have enough integration time.
I want to compare his scope and camera to mine. My guess is his refractor runs circles around mine!
Brian
