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Astronomy: If Andromeda Were Brighter, This is What You’d See

Introversion

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If Andromeda Were Brighter, This is What You’d See

Wait said:
Andromeda is the closest large galaxy to us.

At 140,000 light years across, it’s 40% bigger than our 100,000 light year diameter Milky Way.

Andromeda is 2.5 million light years away from us, or about 25 Milky Way diameters. Here’s a picture to scale:

...

Light takes 2.5 million years to pass between the two galaxies, so if a fancy Andromeda alien is viewing us with a telescope right now, it’s seeing a bunch of Australopithecus walking around being unappealing.

In kilometers, Andromeda is 250 quintillion km away from us. The moon is 400,000 km away, so if you had a ruler that stretched from the Earth to the moon, you’d need 625 trillion of them to reach Andromeda.

And yet, in the scheme of galactic distance, Andromeda is our next door neighbor and one of the only galaxies close enough to be moving toward us—because its “short” distance away means the force of gravity can overpower the movement caused by the expansion of the universe, which in almost all other cases pulls all galaxies away from all other galaxies.

And in about 4 billion years, Andromeda will selfishly collide with the Milky Way and the two will form an extra-huge galaxy. You won’t be here.

Andromeda is also one of the very few objects outside our Milky Way that you can see in the night sky with our naked eye—if you know where to look. It looks like a fuzzy star:

...

But the thing is, it’s so far away that only the super-condensed nucleus of Andromeda is bright enough to be visible to our eye, so that’s all we’re seeing. If the whole galaxy were bright enough, this is what you’d see at night (with the moon as a reference)1:

...

Worth a click for that final picture, IMO...
 

Sophia

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Andromeda is 220,000 light years across, not 140,000, but that just makes it even more amazing. :) You can see more of its huge size in ultraviolet and infrared images taken by space telescopes.
 

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Andromeda is 220,000 light years across, not 140,000, but that just makes it even more amazing. :) You can see more of its huge size in ultraviolet and infrared images taken by space telescopes.

Thanks for the correction!

Recently I learned that it's only been a century since the existence of other galaxies began to be an accepted fact in science? If Andromeda truly were visible as the article's mock photos show, I wonder whether a century ago it would've been assumed to be some more local (in-galaxy) phenomenon, or would've provided earlier proof that the universe is truly vast?
 

Chris P

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I would guess it would be assumed to be a close, smaller neighbor. It's human nature to assume familiar locations are closer than they are. Plus, they had no frame of reference for such a great distance (shoot, we really don't even now.)

This calls to mind the mock ups of what it would look like if the Earth had rings. Just imagine the places in folklore, mythology and religion such things would have if they existed or if we could see them. How different our cultures would be!