Great to see that today’s Astronomy Picture of the Day shows Herschel’s image of the Andromeda Galaxy, M31. Since Herschel operates in the far infrared, what you see in this image is not stars, but dust in M31′s interstellar medium warmed by starlight. The colours represent temperature, so bluer is hotter and redder is colder.
The data that went into that image comes, in part, from the SPIRE consortium, which I’m part of. I’ve even worked on this data a bit, but I’m not responsible for the artistry behind this image.