M 51

M51, the 'Whirlpool Galaxy' in Canes Venatici is famous for its beautiful spiral structure. Its companion galaxy, NGC 5195, (seen to the right of M51 in this image) was discovered in 1781. The M51 system is a spectacular example of interacting galaxies - in this case NGC 5195 is being "ripped apart" by the huge gravitational disturbance of M51, while M51 has in turn undergone huge structural alteration (note crooked upper arm) from the gravitational effects of NGC 5195. The distance of M51 is estimated to be about 37 million light years. The diameter is approximately 100,000 light years and the total mass is estimated to be the equivalent of 160 billion suns.