M33 galaxy through a hydrogen alpha filter. Source
Recently I've been working on a project for my Astronomy class at the University of Iowa. We were given free reign to choose what we wanted to study and my group and I chose to map out the star formation regions of the M33 galaxy. This picture here is of said galaxy through a hydrogen alpha filter. The Ha filter filters out all light that isn't of the same wavelength as the light emitted by hot hydrogen. The benefit of this is that it allows a viewer to identify star formation regions because these regions emit heavily in the hydrogen spectrum, but not very well in any other wavelengths.