Whirlpool Galaxy, composite radio-optical image. The Whirlpool Galaxy (M51a) is locked in a gravitational interaction with the smaller irregular galaxy NGC 5195 (above M51a). M51a is around 50,000 light years in diameter, around half the size of our Milky Way. These two galaxies are around 37 million light years from Earth, in the constellation Canes Venatici. This is the most detailed radio image of the Whirlpool Galaxy ever captured, combining data from the Very Large Array (VLA) and the Hubble Space Telescope (HST) between 2005 and 2012. The optical data is in white and the radio data (C-band) is in red. This is a very rich environment for star formation.