RBA & AF Astrophotography

Andromeda (M31) versus Triangulum (M33)

Posted: September 17th, 2010

This large panorama (a 3x4 mosaic) presents an unusual view that confronts two of the largest galaxies (as seen from Earth) in the night sky: the Andromeda Galaxy (M31) and the Triangulum Galaxy (M33).

The Andromeda Galaxy (top left corner) is a spiral galaxy approximately 2,500,000 light-years away, in the constellation of the same name. The Triangulum Galaxy (bottom right corner) is also a spiral galaxy, at approximately 3 million light years distance in the constellation Triangulum. The bright star in the middle is Mirach, a red giant star about 470 times as luminous as the sun and approximately 200 light years away.

Between them, and invading the entire scene, the often very elusive galactic cirrus clouds can be seen.

Because of the large field of view required to capture these two galaxies in one image, there aren't many images, if any, presenting these two galaxies in the same composition. For that reason, I find this image to be of unusual beauty as well as perhaps a bit thought provoking.


I had to go "at it" several times for several reasons, so in the end the image is a potpourri of data captured in Spain in August, at the DARC Observatory early September, and at the Central Nevada Star Party last weekend. Same scope and camera, but different skies, different exposure times, different amount of subframes, and in one case, even different binning! This mosaic has it all! (BTW I do NOT recommend messing up like that at all - there are "reasons" for all of this, it's just too long of a story :-)

The FOV can be captured - with the FSQ+reducer and the STL11k - as a mosaic of 3x4 (12 frames), but in reality I ended up shooting 26 different frames, each with its LRGBs... This is because once I was done with the data I captured while in Spain, I didn't like the final FOV, so I rotated it, and then I had to capture more frames to "fill up" the holes, then creating seamless frames became very difficult - first because I used different binning and timing, and second because adding frames to an already processed mosaic is often a VERY BAD IDEA. So anyway, I went again and captured more data at the CNSP last weekend to have frames that would match better when building the mosaic. Even with that, some differences can be obvious if you pay attention, but the only way out of it would be to retake the 3x4 frames that make up the FOV and process them all together at once (and I've rather move onto other projects).


I was hoping Mirach (the star in the center) didn't end up dominating the image so much. Knowing how bright it is and that it was going to end up in the middle of the image, this was wishful thinking, but in the end I think it balances the image somewhat ok - kind of like the mid pivot of a seesaw between the two galaxies. Not quite the effect I was hoping for, which was more the effect of "confronting" these two monster galaxies, with the added challenge that the galaxies are very far apart and the attention may get lost, not sure where to focus, and Mirach constantly becoming the safe harbor of our attention, but I think something can be made out of it. Or maybe I'm reading the image backwards!!


The signal from the galactic cirrus is quite real, not artifacts, not gradients. As always, with very faint data, I cannot guarantee absolute precision in the light intensity differences, and only suggest that it's approximate. In any case, if we were to capture it deep enough, and in a perfect world, the cirrus should look a lot wispier than in this image. Instead, it looks more like a blur.

To see what I mean, if I do a heavy stretch on the raw data, I can tell the visible cirrus clouds are quite wispy. Look at this crop of one of the areas (top-middle, though the very top in this stretched image doesn't appear in the final image because it was cropped out):

(yes, in the above image you can clearly see one seam :-)

It would be amazing if this kind of detail could be brought to the final "pretty" image, but unfortunately it was very hard to do, for me at least (it's really dim stuff), so I settled with being able to bring the signal above the noise, but heavily blurred. Also I didn't have a lot of data, so I simply didn't have the know-how or the means of better bringing out this signal that was sitting right with the noise.

BTW the blur doesn't come from applying noise reduction but from separating large and small scale structures in the image. The "à trous" wavelets tool in PixInsight however tends to produce this effect when you abuse it, and although perhaps there's a way to preserve some of this appearance by breaking and processing the image in more than 3 scales, I didn't experiment with that and instead went for what I already know how to do: breaking the image in just 2-3 scale layers (wavelet planes), operating on them separately and then adding them back, rescaling. 



Louie Atalasidis (Contact, Page), September 18th, 2010, 16:08
Hi Rogelio

A unique composition mate...I like It!great work again.



RBA (Contact, Page), September 18th, 2010, 16:10
Thanks Louie! :-)

Monica, Houston, Texas (Contact, Page), September 23rd, 2010, 9:50
Truly beautiful, infinity in motion - many thanx for sharing.

RBA (Contact, Page), September 23rd, 2010, 10:05
Thank you Monica for stopping by and taking the time to let us all know what the image tells you!

Tim Stone (Contact, Page), March 10th, 2011, 20:01
Incredible image, Rogelio. I'm impressed at the scale and also that you've preserved the galactic cirrus. Many times that's just wiped away with a black clip. Also, you've managed to capture NGC 404 (Mirach's Ghost) in this image. Really really lovely.

RBA (Contact, Page), March 10th, 2011, 21:42
Thanks Tim! Glad you liked it!

Vasselle (Contact, Page), September 22nd, 2011, 18:45
superbe image de M31et de M33
et je voulais vous dire continué a nous faire rêvé avec vos photo Astro
elle sont tous magnifique bravo

Robert (Contact, Page), October 14th, 2012, 11:42
woooow.....this mosaic is the best I have ever seen !!!!

Anil (Contact, Page), September 26th, 2013, 12:37
Wow! This is just incredible. Saw it on APOD, and love it. As an astronomer who has published papers on several of the objects in this image (including Mirach's Ghost!), it is a pleasure to see them all together in such a lovely image.

Greg Parker (Contact, Page), October 3rd, 2015, 7:12
You have probably seen that this has been a recent APOD taken by somebody else - so you were 5 years ahead of your time with this one :)

RBA (Contact, Page), October 3rd, 2015, 15:50
The image from Malcom is a composite, with the galaxies "pasted" over a sky captured with a camera lens. Two very different efforts. Thanks Greg! :-)

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