When OS X Lion shipped, Apple used an image of the M31 galaxy in the constellation Andromeda as the default desktop image. Then, when Mountain Lion was announced, the default image changed to a galaxy no one could identify immediately. Now, a reader has tipped us off.

The galaxy, it turns out, is NGC 3190, a spiral galaxy in the constellation Leo (the “Lion”). It’s almost edge on to our line of sight.

The galaxy was the NASA Astronomy Picture of the Day for May 3, 2010. Our thanks to reader Paul Duke who sent us the tip.