The stars are shining tonight
September 11, 2012 1:48 PM   Subscribe

When you look up on a starry night, you see more than a thousand points of light. How many of what we see with the naked eye are stars and how many are galaxies?
posted by megatherium to Science & Nature (9 answers total) 6 users marked this as a favorite
 
Apart from the Milky Way, only the Magellanic Clouds (in the southern hemisphere) and Andromeda Galaxy can be seen with the naked eye. http://curious.astro.cornell.edu/question.php?number=590
posted by plep at 1:50 PM on September 11, 2012 [4 favorites]


It should also be noted, the Andromeda Galaxy is 5° across and is not a little point of light, but rather a huge and very faint smudge.
posted by Kid Charlemagne at 2:14 PM on September 11, 2012


Wikipedia has a slightly longer list of galaxies that can be seen with the naked eye.
posted by yoink at 2:30 PM on September 11, 2012


You can also see the odd nebula and star cluster if you know where to look, plus five of the planets (and the moon, naturally).
posted by Scientist at 2:46 PM on September 11, 2012 [1 favorite]


If you're in a city, or any place with significant light pollution, you can't see any galaxies at all.
posted by Chocolate Pickle at 3:05 PM on September 11, 2012


Quite a few of the Messier objects turn out to be galaxies. When Messier was creating his list of "things in the sky visible to the naked eye which are not comets", he was working without a telescope. Some of the Messier galaxies are quite spectacular e.g. M101.
posted by Chocolate Pickle at 3:11 PM on September 11, 2012


It should also be noted, the Andromeda Galaxy is 5° across and is not a little point of light, but rather a huge and very faint smudge.

I used to do a fair bit of astrophotography back in the day. With a sidereal tracker (mine was home-made with two boards, a hinge and a 1/4" screw) and my Pentax 1000 I got some pretty nice shots over the years. Andromeda is surprisingly big across the sky. You just can't see it with the naked eye or without a long exposure.

Not sure how a common digital camera would measure up to accomplishing the same thing, but damn, that Pentax took some fine long exposure photos.
posted by elendil71 at 3:46 PM on September 11, 2012 [1 favorite]


Assuming you're in the Northern Hemisphere, basically everything that's not a planet or our Moon is a star in the Milky Way. You can see the bulge of Andromeda as a faint smudge if you're in a place with little light pollution, but I'm fairly skeptical of the other northern hemisphere "naked eye galaxies" on the linked Wikipedia page. You'll notice that some of them are "one guy claims to have seen this."

If you're in the southern hemisphere, add the LMC, SMC, and Omega Cen (whether this last one is truly a galaxy is up for debate).

Messier used a telescope, so most Messier objects are not visible with the naked eye.
posted by Betelgeuse at 6:36 PM on September 11, 2012 [1 favorite]


Assuming you have perfect seeing (not eyesight, but seeing, i.e. viewing conditions, as far as weather, ambient light, etc.) at sea level, the human eye should see all stars brighter than (apparent) magnitude +6. (brightness increases 10 times with every magnitude, but lower numbers = brighter-- the sun is a -26 magnitude for example, while +6 is very dim). Some sources say +6.5 or +7, but I don't know how that affects the below number, which I'm told correlates to +6.

That works out to about 6000 visible stars in the sky, or roughly 3000 visible in a given hemisphere in an instant.
posted by Sunburnt at 10:27 AM on September 12, 2012


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