Thursday, February 23, 2012

Alternative views of M31 and M104

I created the following images while doing class prep for my astro class and thought they might be of interest. I wanted to show how M31 would look from a view above one of its poles, so I tried to compensate for the foreshortening we see because of its inclination to us. The goal was to show the central bar more clearly for those who have trouble seeing it.
M31: Visible light (left) and Infrared (right, Spitzer NASA/JPL/CalTech)

the left image is one of mine, and the second is a Spitzer image from NASA/JPL and CalTech. My image of M31 is not so hot; if you want to try this yourself, you would do better to start with this amazing image. I think I've got the two images reasonably aligned and scaled to match. The brightest portions of the Spitzer image coincide with the dark dust lanes in the visible-light image.

You might find this fun to do with other inclined galaxies. It won't work with very nearly edge-on galaxies. Here's the Sombrero, for example:
M104 (Sombrero Galaxy, NASA Hubble)

Notice how the central bulge obscures the more distant portion of the dust/gas ring.

To remove foreshortening first rotate an image so that the long axis of the galaxy is either horizontal or vertical. Then resize the image, stretching it greater in the direction of its thinnest axis. (Make sure to turn off your graphics program's preservation of the aspect ratio.) Adjust the stretch amount until you have the galaxy looking round and you're done. We assume the galaxy is round, but that's not always the case. It's a decent first guess.

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