Thursday, October 27, 2016

Andromeda Galaxy (M31) and the satellite galaxies M32 and M110

Andromeda Galaxy – produced from 186 RAW images of 9 minute and 21 seconds of exposure in total stacked using Deep Sky Stacker (DSS); individual images were of 105mm on a full frame Canon DSLR, ISO 8000; 3.2 seconds of exposure each, Custom White Balance at 3500 Kelvin,; the final image is cropped to make Andromeda fill a good percentage of the frame. Its neighboring satellite galaxy M110  is visible towards the upper right part of Andromeda and its brightest satellite galaxy M32 is visible as a fuzzy spot towards bottom of the core at the edge of the disk of Andromeda) 

Andromeda, now classified as the nearest major galaxy from Milky Way, which was once catalogued as the Great Andromeda Nebula, is the largest in the local group of galaxies in our neighborhood. It lies approximately two and a half million light years from earth and holds almost one trillion stars (10 raised to the power of 12) which means about double the star count in Milky Way.

I thought that it was impossible to capture a picture of Andromeda with a just DSLR unless aided by a telescope and a costly equatorial mount. But after reading a few articles on internet, I decided to give it a try. 24th October 2016 was a moonless clear sky night for Donegal and probably the entire Ireland. We (me and my friend Vinu Padbanabhan) set out to a secret dark location in Donegal around 11:00 pm and reached the location at midnight, the sky was astoundingly clear and dark enough that the Milky Way band was clearly identifiable as soon as the car’s headlights were turned off. Not a single source of light was seen 360 degrees around and no moon!

Here is how the final picture posted above was achieved. After indentifying a few well known asterisms, I was able to locate the approximate direction of Andromeda in the sky, I never had identified Andromeda before but I had read that it is visible to the naked eye on a clear night sky. After a few minutes I found the faint star like fuzzy spot which could be Andromeda. After setting the DSLR in manual mode, maximum ISO, auto focus turned off, manually focused at the near infinity mark, maximum aperture and maximum zoom (105mm on the 24mm-105mm lens on a full frame Canon); I pointed the tripod mounted camera to the approximate direction. I took a few shots with 20 seconds of exposure time, but couldn’t find Andromeda other than stars on the image. Every time I couldn’t find the galaxy in the image, I changed the direction slightly around the approximated location (it is very difficult to point the camera at a faint object in a dark sky as we cannot see stars through the view finder eye piece).

The final non cropped stacked image stacked using Deep Sky Stacker from 186 images

At last, I found half of the fuzzy patch at the bottom line of an image. I then carefully tilted the tripod a few times in between the next few shots so that the fuzzy patch is in the center of the frame. After calculating the direction of rotation of the stars (located the Polaris - the Pole Star and imagined the circle that Andromeda would trace in the next one hour around Polaris), the camera was aligned again by carefully tilting the camera between each shots so that the fuzzy smear of Andromeda appears in the center left of the frame and moves across to the frame to the center right when earth rotates.

 The ISO was then set to 8000 after repeated trial shots by setting the exposure to 3.2 seconds (applying the 500/focal length rule to prevent star trails, 4.75 seconds turned out to be the maximum exposure time at 105 mm), the white balance was set to color temperature of 3500 Kelvin. This entire process took around 45 minutes.

Since an intervalometer was not built-in on my camera, I installed the custom firmware Magic Lantern and used its intervalometer feature to take continuous shots with the above settings. By this time, my fingers were frozen in the cold weather of 5 degrees Celsius outside; it was very difficult to operate the buttons on the camera.

An individual unprocessed image from the 186 samples used to create the final image, note that Andromeda appears in the center as a fuzzy smear in this image
Leaving the camera alone to take continuous shots, we got into the car and turned the engine on to escape the cold weather outside as well as to prevent lens fogging (the camera was placed close to the front radiator grill of the car). A few 100 shots were taken in the next half an hour but when I inspected the camera, I found that the lens got fog on it, I checked the last few images and verified that Andromeda has moved towards the center of the frame by this time. I took the camera inside the car to heat it up and remove the fog from it, and then when it was all clear, placed the tripod much closer to the radiator grill, and repeated the alignment process all over again to have Andromeda on the left center of the frame, and left the camera on intervalometer feature to take as many shots.

Around 800 images were taken in the next 45 minutes and this time no lens fogging occurred, we took a few more wide-angle pictures of the Milky Way band and the starry sky and then packed up the equipments, drove back and reached Letterkenny by 03:30 am.

In the next few days I kept on processing the raw images multiple times and stacked the images in various combinations using deep sky tracker(DSS) software to get a satisfactory image of Andromeda and the final cropped image was produced.

To my surprise the satellite galaxies of Andromeda namely M110 and M32 turned out to be visible in the final cropped image.


  1. wow ! I would love to start my astrophotography journey sometime in near future !

    1. Warning!!! be caereful :) as you dive deep into Astrophotography, it becomes an expensive hobby very soon. But I wouldn't discourage, it is a fantastic hobby

  2. Wow awesome dedication, appreciate it buddy!!!

  3. Which DSLR, what are the lenses used?
    It's brilliant