RE: Science Porn
November 27, 2014 at 6:06 pm
(This post was last modified: November 27, 2014 at 6:13 pm by Jackalope.)
(November 27, 2014 at 12:47 am)Chuck Wrote:(November 26, 2014 at 11:04 pm)SteelCurtain Wrote: More fun with scales:
That's far from accurate. The furthest stars easily visible to the naked eye even in relatively light polluted areas like Los angeles are those of the andromeda Galaxy 2.5 million light years away, or a distance equal to about 20 times the diameter of a typical large spiral galaxy implied here. Admittedly I am talking about seeing a collection of stars, not resolving a single star.
The furthest single star that can be resolved by the naked eye would be blue supergiants. These can be seen out to about 5000 light years. So a circle encompassing the further individual stars visible to the naked eye would still be 1/10 the diameter of a typical large spiral galaxy - ie far larger relative to the Galaxy than the yellow circle in the picture.
You make a good point, that the distance at which stars are visible is dependent on their intrisic brightness and intervening dust, in addition to distance.
Visibility of M31 from urban skies is pretty iffy. Its pretty reliably visible (if you know where to look and what you're looking for) from my country property 30 miles north of Portland, but from the city itself, I've never been able to spot it unaided. Typical magnitude limit is 3ish. Yeah, M31 is bright, but that brightness is spread out over a very large area - and good luck resolving individual stars. ;-). Can't even do that with my 200mm Schmidt-Cassegrain (couldn't do it with my 300mm reflector either, before I sold it).
The brightest stars you can see? Most of them are really close, relatively speaking. I've seen sources that claim 4000 ly for the brightest supergiants under mag 6.5 skies (average eyes, very dark skies). 5000 ly for exceptionally dark skies and eyesight seems within the realm of possibility.