Thursday, September 3, 2015

visible light - At what distance could you see andromeda with the naked eye?



We've all seen the telescope photographs of andromeda galaxy: enter image description here


I'm wondering if it were possible to travel close enough to the andromeda galaxy could you achieve a same perspective with the naked eye? What distance away from andromeda would give you the same vantage point as the photograph to the point that you could take the same photograph with a regular point and shoot camera?


I assume you would be in intergalactic space between andromeda and the milky way.


On that note, if you were halfway between the two, would you be able to clearly make out both galaxies in their entirety or would you simply see 2 points of light that more resemble stars than galaxies?



Answer



Well, First off, you can see the Andromeda galaxy with your naked eye from a dark place on a clear night. You should try it if you can. It looks like a smudge of appreciable size, not like a point. So half way between the Milky way and Andromeda, both would look like smudges twice as wide as Andromeda does from earth. I think a standard point and shoot camera is slightly better than the naked eye, but not a whole lot. The other way to think about it is to consider the power of the lens used to take the picture. Telescopes are usually between 10 and 100 power, although more is possible. A point and shoot is usually 1-3X I think. The naked eye is 1X of course. But long exposures "see" much more than the naked eye. So to get 10X you would need to be 90% of the way to Andromeda so the remaing distance is 1/10th of the way to Andromeda, to get 33X power equivalent, you would need to be 97% of the way to Andromeda, etc. I am guessing you would see some structure at 10X, particularly with a long exposure from space, but to get the equivalent of the truly excellent pictures you see on the web or in astronomy magazines you might have to go to 33X or even 100X. For 100X you would have to go 99% of the way to Andromeda. Again, your point and shoot with a long exposure is probably three to ten times better than your naked eye.


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