Astronomy Picture of the Day

Explanation: The Whirlpool Galaxy is a classic spiral galaxy. At only 23 million light years distant and fully 65 thousand light years across, M51, also known as NGC 5194, is one of the brightest and most picturesque galaxies on the sky. The smaller galaxy appearing here below and to the left is well behind M51, as can be inferred by the dust in a foreground spiral arm blocking light from this smaller galaxy. The Whirlpool, pictured above, is visible with binoculars in the constellation of Canes Venaciti. M51 is a spiral galaxy of type Sc and is the dominant member of a whole group of galaxies. Astronomers speculate that M51's spiral structure is primarily due to its gravitational interaction with this smaller galaxy.