When my grandmother went to school, nobody knew that galaxies existed beyond the Milky Way. But with today’s telescopes at least 10 billion can be detected, each with hundreds of billions of suns and probably an equally staggering array of planets, moons, and who knows what else. Yet the average educated person can name only one galaxy other than our own. That single galaxy has so entered our vocabulary that it has become the galactic paradigm, the most famous by far: Andromeda.
One reason for its renown is its fortunate overhead position above North America and Europe, where it’s perfectly placed for observation each autumn. Probably another factor is its mellifluous name. After all, the galaxy M87 is bigger, M82 more violent, Centaurus A more mysterious. But none has the euphonious appeal of Andromeda, a name too lovely to forget.
Andromeda is also the nearest spiral galaxy to us. It’s very much our sister galaxy, although it has about twice the mass of the Milky Way. But its greatest draw may simply be that it’s there, visible to the unaided eye.
From north of the tropics, the only naked-eye view we have of a galaxy is Andromeda. Even the lavish star fields that spill across October’s skies like blowing sand, so seemingly infinite, lie no farther than a few thousand light-years. Among those stars, but a thousand times more distant, Andromeda’s ghostly glowing smudge could easily pass for a faint fragment of cloud, utterly camouflaged in bright city skies.
How distant? Astronauts who need three days to touch the moon would require 500 billion years to reach Andromeda, dozens of times longer than the universe has existed. Like snowflakes blown against a window, the night’s stars are mere foreground specks bearing no spatial connection to that enormous object looming in the distance.
It’s big, all right. Otherwise, how could something so remote take up 4 degrees of our sky? When seen through binoculars, its brighter central section appears larger than the moon, which in reality takes up only a half degree. Its enormousness might be grasped by comparing distances: moonlight reaches our eyes after traveling less than two seconds, while Andromeda’s frozen portrait arrives after hurtling through space for over 2 million years!
If Andromeda is large in our sky, it must be simply awesome through a big telescope, right?
Despite the disease of high-poweritis that temporarily afflicts most beginners, many celestial objects look best under low magnification, and Andromeda is a perfect example. The biggest problem is obtaining sufficiently low power so that the whole galaxy can fit in the field of view. Through most telescopes the task is impossible. Andromeda is just too big, and only a small, nebulous, unimpressive section can be seen at a time.
Like its mythological eponym, Andromeda is chained to the rock of our own gravity and will always linger next door. While nearly every other galaxy has joined the let’s fly away from the Milky Way bandwagon, Andromeda is one of about two dozen known--the local group--that loiter too close to participate in the expansion.
So whatever the fate of the universe, we’ll occupy adjacent seats for the show, reason enough to take a peek as Andromeda passes high overhead these nights, near the W-shaped constellation Cassiopeia. If more motivation is needed, we might simply recall that when we look at Andromeda, we’re encountering the farthest thing the eye can see.