This is an image of the Andromeda Galaxy (also known as Messier 31), created from data taken by the Sloan Digital Sky Survey. SDSS uses a 2.5m telescope in New Mexico and has imaged a quarter of the sky (as well as doing an amazing amount of spectroscopy), and its data is publicly available online. However, while that data is very high quality and extremely uniform for such a wide area, the usual generation of images for the web sometimes has a few artifacts, often near very bright objects. Andromeda, the nearest large galaxy to us, suffers from some of these issues.
I've applied some other tools to the data to make what I hope is a more pleasing image to explore, although the brightness of each pixel is less straightforwardly linked to the actual brightness observed.
SDSS imaging is broken down by what are called 'fields', which are 2048 by 1489 pixels in size. Each pixel is 0.4 arcseconds (an arcsecond is 1/3600th of a degree), so each field is up to a little over 0.2 degrees across. Since M31 is several degrees across I've taken a large number of fields around the M31 area and stitched them together, using the overlaps between fields to model and correct for any differences between them, giving a single image a bit over 2.5 degrees on a side. This is made super-easy by the Montage software. I did this for three of the filters SDSS uses (g, r and i) to create a 587 megapixel result in each of those three bands.
Astronomical data has a tremendous dynamic range - the brightest things in an image can be vastly brighter than the faintest things. I applied hand-picked stretches to bring that vast dynamic range back into something that can be viewed on a monitor and have both bright and faint detail readily observable, as well as to correct the white balance. I did some extra background correction to deal with some remaining differences in the background illumination (although others still remain), and then I also applied 'wavelet transformations', which change brightnesses of larger structures than a single pixel in order to bring out certain features. I did all of this using the excellent PixInsight (an amazing tool I recommend for both amateur and professional astronomers seeking to make visually stunning images).
Finally, I needed to get this enormous image on to the web. I used jQuery tiles for this task.
All in all the credit for this is almost entirely down to the amazing work of SDSS astronomers for making such high quality data so readily accessible, and the programmers of Montage, PixInsight and jQuery tiles, who made this task fundamentally easy (if still computationally time consuming!). See the credits and acknowledgements page for full details.
Yes, there are a few. The Hubble Space Telescope has imaged a large part of it (about a third) as the Panchromatic Hubble Andromeda Treasury or PHAT. Since it's HST the data for that has 3 to 8 times the resolution of SDSS (depending on the band - two different cameras on HST were used).
Robert Gendler has an amazing 317 megapixel image of M31. It's an astonishing image which certainly took more effort on his part than this did on mine (I didn't take the data that made this image!), and it's all the more impressive for having been done with a telescope with 25 times less collecting area. It looks to be very very well mosaiced too.
Elmo Tempel and Taavi Tuvikene have also produced a mosaic of Andromeda from the same data as me. Theirs is 425 megapixels, covering a wider area than the one here, but at half the resolution. On the other hand they've done a much better job of modelling the varying backgrounds - science quality in fact.
I'm Edd Edmondson. When I made this, I worked at the Institute of Cosmology and Gravitation at the University of Portsmouth, which is a member of the SDSS-III collaboration. You can email me at eddedmondson@gmail.com and I'm on that Twitter thing.
I may do some other objects in this way in the future, but if you like looking at pictures of galaxies I have to recommend Galaxy Zoo (of which we are also a part), which will let you look not only at images of many other galaxies but help us do science with them too. You should also check out Galaxy Zoo's sister the Andromeda Project, which lets you go through the incredibly high resolution images of M31 from PHAT (mentioned above).
