6/11/2010: Hydrogen in M51, NGC 5194. Perhaps the first spiral nebula, M51 is a large galaxy, over 60,000 ly across, with a readily apparent spiral structure. M51 is a part of a well-known interacting galaxy pair, its spiral arms and and dust lanes clearly sweeping in front of companion galaxy NGC 5195 (top).
Also known as NGC 253, the Sculptor galaxy is part of a cluster of galaxies visible to observers in the Southern hemisphere. It is known as a starburst galaxy for the extraordinarily strong star formation in its nucleus. - Image: NASA/JPL-Caltech