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This is the Whirlpool galaxy (also known as M51a or NGC 5194) and its companion galaxy M51b (also known as 5195). Both galaxies are located about 23-million light-years from Earth, in the constellation Canes Venatici. The galaxy pairing is easily visible to amateur astronomers and can be seen with binoculars, making M51 one of the most well known galaxies in the night sky. Both galaxies are collectively referred to as M51, though it isn’t uncommon for people to use the designation to refer only to the Whirlpool galaxy.

 

The Whirlpool galaxy itself is an interacting, grand-design galaxy. M51a is ‘interacting’ because it’s interacting gravitationally with M51b, and ‘grand-design’ because it has very well-defined spiral arms (not unlike our Milky Way). Gravitational forces exerted on the Whirlpool galaxy by its companion are helping to drive M51a’s star formation. You can see the fruits of this interaction by looking at the bright blue star clusters (the largest concentrations being closest to M51b). Within these blue pockets are the youngest stars in the Whirlpool Galaxy. In contrast, the oldest stars can be found near the Whirlpool’s central bulge.

 

There are a few foreground stars seen here. These stars are ‘large’ bright balls and have the starring photographic effect. These stars are located within our own Milky Way. Again, in contrast, in the background you can see several galaxies which are much further away than the Whirlpool – many of which appear red due to the effects of redshifting.


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