Messier 51 is a rather pretty spiral galaxy, sometimes known as the Whirlpool Galaxy. Unfortunately, as a spiral galaxy is basically a big swirly thing, there are a few others which people mis-identify as “whirlpool galaxy” too. The real whirlpool galaxy is easily remembered by the companion galaxy, NGC 5195, with which it’s interracting. Together, the two always remind me of Scylla and Charybdis from greek mythology…