Andromeda and the Milky Way just keep getting closer

The Andromeda Galaxy (NASA)

Until 1925, nobody knew that galaxies existed beyond our own Milky Way. With today’s telescopes, 200 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. That single galaxy is the most famous by far: Andromeda!

One reason for its renown is its fortunate overhead position, 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 and, oddly, the largest in this whole section of the universe. You’d have to venture 40 million light-years to find anything bigger. But its greatest draw may simply be that it’s visible to the unaided eye in rural regions like ours.

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. Amongst those stars but a thousand times more distant, Andromeda’s ghostly glowing smudge could easily pass for a faint fragment of cloud.

How distant? Astronauts traveling fast enough to touch the Moon in just three days would require 500 billion years to reach Andromeda. 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. Moonlight reaches our eyes after traveling less than two seconds, while Andromeda’s frozen portrait arrives after hurtling through space for 2 ½ million years.

If Andromeda’s so large in our sky, it must be simply awesome through a big telescope, right? Wrong! Despite the disease of high-poweritis that temporarily afflicts most beginners, many celestial objects look best under low magnification, and Andromeda’s a perfect example. The biggest problem is obtaining a sufficiently low power so that the whole galaxy can fit in the field of view. Through most telescopes the task is impossible. Andromeda’s just too big, and only a small, nebulous, unimpressive section can be seen at a time.

By sheer coincidence, the nearly edgewise appearance of Andromeda matches the view that any Andromedans would have of us. The fact that Andromeda appears near the Milky Way in our night sky automatically tells us that from there, we too are oriented sideways. It’s almost as if there’s a giant mirror out there, and we’re seeing ourselves.

It’s a safe bet that intelligent life gazes upward from numerous Andromedan planets, curious about our own smudgy galaxy. Do they realize, as we do, that our two systems are approaching each other? With the separation decreasing by 70 miles each second, we’ll collide in five billion years. But no problem: We’ll pass through each other without harm, since the constituent stars are too far apart for individual contact. Ultimately, our two cities of suns will merge into an enormous new galaxy that has already been named: Milkomeda.

So we’ll always hang out together. Like its mythological namesake, Andromeda’s chained to the rock of our own gravity. While virtually every galaxy has hopped aboard the “Let’s fly away from the Milky Way” bandwagon, Andromeda’s one of just two dozen that loiter too close to participate in the universe’s expansion. In a Cosmos where the red shift is as commonplace as pizza, Andromeda displays the rare blue shift.

It’s our roommate, our eternal companion: reason enough to take a peek as it passes high overhead at midnight – the farthest thing that the eye can see.

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