Imaging Supernovae

Imaging Supernovae

Professional astronomers distinguish between two main classes of supernovae. The distinctions have to do with the type of explosion occurring, how it is triggered, the resulting light curve and the atomic elements visible in the spectrum of the supernova. However, for amateur astronomers' purposes we can consider two very basic types of supernova: galactic and extragalactic. Our primary concern is with extragalactic supernovae, as a galactic supernovae is far more infrequent an event than even a brilliant comet, solar eclipse, or any of a number of other "rare" astronomical phenomena. In fact, more than a dozen generations have passed without any human witnessing a supernova in our own Milky Way galaxy! If one occurs it will certainly be front-page news, so don't worry about missing out on that event!

Finding Extragalactic Supernovae

Imaging supernovae essentially involves imaging galaxies. There are few other considerations than those normally applied to capturing a CCD image of a distant galaxy. Supernovae usually occupy the briefest time span of the three main transient events discussed in this section. Comets are often visible for weeks or even months, and even rapidly-moving near-Earth asteroids stick around for a week or more. Supernovae on the other hand may last only a few nights, appearing as a single brilliant star outshining the light of 100 billion companions in its host galaxy.

A good resource for current supernovae is the International Astronomical Union's list of Recent Supernovae:

http://cfa-www.harvard.edu/iau/lists/RecentSupernovae.html

The list gives the latest discoveries and the name of the host galaxy (or position if the host galaxy is uncataloged). Due to the short time available to image supernovae, subscribing to the IAU Circular is recommended as well. This email circular lists recent astronomical headlines including supernovae, novae, comets, interesting asteroids, and other events. Often the information in the circular is not available immediately through any other source.

Photometric (brightness) measurements can be made of a supernova as it fades. This information tells scientists about the type of explosion and can even lead to information about the distance to the host galaxy or the redshift (recessional velocity) of that galaxy, leading to a better understanding of the universe.

How About a Nova in the Meantime?

While we all await the next galactic supernova to flare up and outshine all the other stars and planets, there is a similar event which occurs on a smaller scale but also more frequently. A nova is a stellar explosion, orders of magnitude smaller than a supernova, but often impressive as a rare astronomical phenomenon. Novae are stars within our galaxy which outburst every so often, causing a previously invisible star to brighten suddenly, sometimes to naked-eye visibility. Imaging a nova involves nothing more than imaging a star field, but again the event is transient and may last only a week or so (unless exceptionally bright, in which case it may last a month or more). Watching the latest astronomical headlines is always a good idea! Taking an image after the nova has faded (or several over the course of its fading) allows a glimpse into the life of an unusual star.