Wednesday, September 4, 2013

Starting the Next Andromeda Season with Baby Steps

We're getting to the point in the year when the Andromeda Galaxy (M31) is above the Indiana haze at around 11:30pm - so it's the earliest in the season to attempt a decent Andromeda stack. My previous attempt was back in January when I was first learning how to use Deep Sky Stacker - and while I haven't had too much practice since then, I figured I could do a little better.

For comparison, my previous attempt was during a gibbous moon with 318 light frames. This time around, I had a new moon and 667 light frames (but I chose to keep the best 80%, so an effective 534 total subs). Total exposure time is around 11 minutes. Images were taken with Canon Rebel XT (350D) on a fixed tripod.

Messier 31 andromeda 300mm
Stack of 534 subs, 94 darks, 104 bias, f/5.6, 300mm, ISO 1600, 1.3 sec each
Layered with my previous image at 30% transparency

It's definitely more recognizable than just a fuzzy blob! Granted, it's got plenty of fuzz and blob to go around. I try to remind myself that this is with a relatively slow lens and 8 megapixel camera (Canon Rebel XT) so it's not going to be Hubble quality. It's a baby step, and my best Andromeda to date! Still, after two nights of shooting, 4 hours of image stacking, and 2 hours of image processing, I had high expectations!

Messier 31 andromeda galaxy label
Dust trails are visible on M31 as darker lines on the top ridge. M110 and M32 are featureless but visible nonetheless.
Andromeda image processing
Baby steps, improvement over my first Andromeda attempt

Update: Planning my shot...

Jason in the comments asked for an unprocessed light frame, but I can do one better. Here is some more info on how I planned out the shot.

andromeda star chart
First I find the right general area by star-hopping from Mirach to the left

andromeda 8 second exposure
Then I scan the area at ISO 1600 with 8 second exposures until I get Andromeda framed correctly. In this case, in the bottom 1/3 of the frame. This is because the sky will appear to move upward, so Andromeda will be centered as long as possible.

andromeda fixed tripod frame
After getting Andromeda in the right spot in my field of view, I switch to 1.3 sec exposures to avoid star trails following the 600 rule (600 ÷ 1.6 (my image sensor crop factor) ÷ 300 (focal length) = 1.25 sec


  1. Could you post one of your light frames unprocessed please? I tried photographing M31 with my new cameraa couple of nights ago but I couldn't even locate it with binoculars! I took a few photos of the general Cassiopeia area and I've pinpointed where it should be, but there's nothing in the picture. I think there may be too much light pollution where I am and o just want to see a comparison photo before I spend a lot of time taking shots for a stack!


  2. Hi Jason, I added some more content to the bottom of the post. I hope this helps! Instead of binoculars I'd try locating it with an 8 sec exposure and looking for a fuzzy blob.

  3. Thanks! I've got clear skies forecast tonight so I'll give it another shot