Whirlpool Galaxy

One of the most photogenic galaxies in the sky — a grand-design spiral interacting with its smaller companion NGC 5195 in Canes Venatici, about 23 million light-years away. M51 was the first galaxy where spiral structure was observed (by Lord Rosse in 1845). The interaction with NGC 5195 is compressing gas in M51’s arms and triggering intense star formation, visible as bright pink HII regions strung along the spiral arms like beads. A rewarding target that reveals more detail with every hour of integration.