Quote:
Originally Posted by metal_geek
Try explaining anything "Astronomy" releated to anyone and scale and perceptions goes out the window.
I was showing a friend of mine the Andromeda galaxy one night, and I said "It's about 100,000 light years across and 2.5 million light years away!!!.." and he being rather unimpressed said "I would have thought 100,000 light years would be bigger"...
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I realize this is not what your friend had in mind, but 40kpc diameter viewed at 800kpc away results in an angular diameter of ~ d/D ~ 40/800 ~ rad/20 ~ 3 degrees of arc on the celestial sphere. For reference, the moon is about 30 arcminutes, or 0.5 degrees. This makes Andromeda 6 times "larger" (6 times the angular diameter) than the moon. That is pretty big. And considerably bigger than what you actually see in the sky, because you only see the central part of the galaxy with the naked eye. So really, your friend was right when he made that statement, albeit for the wrong reasons.