M33
This image shows a section of M33, one of the two nearest spiral galaxies to our own Milky Way. M33
is so close (830,000 parsecs, or 2.7 million light-years) that it is actually possible to resolve its brightest
stars from the ground, particular if the seeing is spectacular, as it was when these images were taken (0.8 arcsecond). The blue stars in this picture are hot massive stars, and the yellow disk and bulge consists of
billions of unresolved stars like the sun. The red extended objects are gas clouds like the Orion nebula, known as H II regions. The large gas cloud at upper left is known as NGC 604, and is one of the largest H II regions known, harboring thousands of massive stars, 40 times the size of the Orion nebula. This
image was taken in order to measure the light fluctuations of a set of binaries (double stars) that contain
Wolf-Rayet stars, a type of evolved massive star.
Image credit: Neugent/Pugh/Massey/DCT/NSF