NGC 3310 and Supernova 1991N

In 1991 a supernova went off near the nucleus of the unusual spiral galaxy NGC3310. This picture shows both a before (bottom, April 1987) image and an after (top, April 5th 1991) image of the central region of the galaxy. Supernova 1991N was apparently first detected on March 29th and announced in an I.A.U. Telegram on March 30th, so that it is seen here when it was quite close to maximum brightness. This picture shows dramatically how bright a supernova can be, since it clearly outshines the nucleus and, indeed, rivals the entire output of its host galaxy. Spectroscopic observations of the supernova were strongly contaminated by the underlying bright ring, but it seems to have been of type Ic, or possibly Ib. The other bright spot on the lower right of each frame is one of the brightest and most distant known HII regions. NGC3310 is a peculiar active galaxy.