M33, ISO
M33 is a nearby example of a spiral galaxy. It is only slightly inclined to our line of sight such that we can see both structure in the spiral arms, and the central bulge. Observations of galaxies like these can help us determine the structure of our own Galaxy, the Milky Way.

This image shows M33 in infra-red light (at a wavelength of 60 microns) from the Infrared Space Observatory (ISO). As well as tracing populations of cooler stars, photons in this part of the spectrum trace the warm dust found in regions where new stars are forming. The young stars illuminate the surrounding gas which absorbs he light and re-radiates it in the infra-red.

Image credit: ISO