The Whirlpool Galaxy

Located 21 million light years away in the constellation Canes Venatici (just below the handle of the big dipper). This was the first galaxy to be classified as a "spiral" galaxy. Estimated diameter is 76,000 light years with a mass of approx 10% of the milky way galaxy. M51 is also known as NGC 5194 and can be seen interacting with NGC 5195, a dwarf galaxy. These two are the most famous of interacting galaxy pairs.