Sky watch: Distant galaxy Great Andromeda

A long time ago in a galaxy far, far away, a beam of light began its journey through the cosmos.

At the speed of 186,282 miles per second, this beam could orbit our planet nearly 450 times in just one minute. But it wasn't orbiting our world . . . it was coming from another galaxy.

Its journey began some 2.4 million years ago -- long before the ice ages carved the land on which we live. on one cool October evening in 2011, this travel-weary light beam will encounter a tiny blue world in orbit around a G2V star near the edge of its own galaxy. Within only one-thousandth of a second, it'll slice through this planet's atmosphere and enter the upturned eye of a stargazer.

It is here that its voyage comes to an end -- in the eye of a terrestrial stargazer 14.4 million trillion miles from its home: the Great Andromeda Galaxy, also known to astronomers as M31.

cast your gaze high into the northeastern sky. Find the four stars of the Great Square of Pegasus. If you follow a line from the square's northeastern-most corner to its southwestern-most corner and continue along that path, you'll soon encounter a faint, elongated smudge that is M31.

You can also use the topmost three stars of the constellation Cassiopeia to point in its direction. In fact, the galaxy lies at the intersection of those two lines.

Originally believed to be one of the nearest clouds of gas and dust in our Milky Way, it wasn't until the early decades of the 20th century that astronomers discovered that it was actually a galaxy in its own right, and the farthest object visible to the unaided eye.

With binoculars, you'll be amazed at the immensity of M31. Even from its great distance, this pinwheel of hundreds of billions of suns -- a galaxy half-again as large as our own Milky Way -- spans an area of sky 12 times larger than the full moon. And it's absolutely breathtaking.

As you gaze at its faint glow, ponder the journey made by the photons of light that stimulate your retina at that very moment. And if you don't shiver with amazement . . . well, you may just not be human!