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"And given that it’s 2.5 million light years away, the surprising amount of sky space Andromeda takes up speaks to just how ridiculously large a 140,000 light y
by robbrown451 6y ago
"And given that it’s 2.5 million light years away, the surprising amount of sky space Andromeda takes up speaks to just how ridiculously large a 140,000 light year diameter galaxy is."
Well, not really. I mean, that doesn't tell me anything about its hugeness, because apparent size is based on a ratio. They're making a ratio with light years on both sides, so they effectively cancel out. 2.5 million / 140,000 is 17.8. So Andromeda is only 17.8 times as far away from us as its diameter. (which is, to me, a very interesting takeaway)
You could substitute "millimeters" for "light years" and it would appear the same size, i.e. a 459 foot diameter object that is 8200 feet away would have the same apparent size as Andromeda.
Not trying to criticize the article, but thought it was an interesting way they put it.
- unwind 6y agoThat's of course true, but I think it's a pretty big part of the context that "the object" is a galaxy, i.e. a collection of approximately 1 trillion (1,000,000,000,000) stars. It's more or less obvious that such an object cannot be very close, and thus it's apparent size in our sky really does convey something about its size. That was my interpretation, at least.
- robbrown451 6y agoIf you could see the galaxy as brightly as in the photos, there's nothing to indicate its size, at least not directly. You are saying it can't be close because it has a trillion stars, and we know stars are big, therefore it is big, therefore it must be far away, and then back to therefore it is big. Isn't that kind of circular? I could imagine ancient people seeing a galaxy that size (if it was bright enough), and guessing it was a few hundred miles away and under a hundred miles across.