M51 - the Whirpool Galaxy
[The Whirlpool Galaxy], M51, is probably the best known galaxy in the sky - it clearly shows spiral structure and is probably one of the first images most people will think of when thinking of galaxies. It is better described as a grand-spiral galaxy, [SA(s)]. It is some [23 million light years away] but is clearly visible with a pair of binoculars and some steady hands (it can be found in the constellation of Canes Venatici). Interestingly, the companion galaxy seen at the end of the whirlpool (NGC 5195) is actually interacting. The gas in the galaxy is disturbed as the result compression, common in galaxy interactions, causes formation of new stars!
Oh and being a radio astronomer I think I should also point out this cool image of [M51 at 21cm] - not many galaxies are resolved like this at radio wavelengths.
This photo was short-listed in the the Astronomy Photographer of the Year 2009 competition.
![[M51 at 21cm]](http://www.mpifr-bonn.mpg.de/staff/wsherwood/Images/m51cm20i.gif){kind=link}