Number of stars visible with the naked eye.

[vanillacoke]

I remember reading some place that on a clear night up to ten thousand stars are visible. How did they figure that one out? I'm picturing some guy with a telescope, pen and paper counting away all night. What's the secret? Computer magic? Photography?

 

[doubletruncation]

Originally, yes, it would have been people charting down all the stars they saw by eye using a sextant or some scheme to get the positions. This goes back to Hipparchos in 150 BC (who charted something like 850 stars) and then Ptolemy from 150 AD or so who charted 1028 stars in his Amalgest (these catalogues only covered the part of the sky visible to these observers, so not all of the southern hemisphere is included). Others followed up on this (notable names include Tycho Brahe who was the last to do this sort of thing without a telescope and John Flamsteed). Probably someone else can give a more detailed history than I can.<br /><br />At the beginning of the last century astronomers started using photographic plates to make the catalogues. They would take pictures with their telescopes and then catalogue the stars that they found on the images, by eye. The biggest catalogue done in this fashion was the Henry-Draper catalogue ( http://www.answers.com/topic/henry-draper-catalogue ) which has some 200,000 stars (which were catalogued by a group of women working at the Harvard College Observatory who systematically recorded the stars they saw on the photographs) including stars much fainter than can be seen by the naked eye. <br /><br />Modern catalogues, such as the Guide Star Catalogue, the USNO A and B catalogues, the 2 Micron All-Sky Survey catalogue, and the Sloan Digital Sky Survey, are all done automatically using robotic telescopes to image the sky and then computers to search the images for stars or other sources of light.<br /><br />The modern catalogue of stars brighter than the visible limit (taken to be 6.5 magnitudes which is about 1000 times fainter than the brightest star, Sirius, and only visible on a very clear night for someone with excellent eyesight) is the Yale Bright star catalogue ( http://www.alcyone.d <div class="Discussion_UserSignature"> </div>

 

[alokmohan]

Around 6000 stars are visible by naked eye.

 

[MeteorWayne]

And you know this how? <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>

 

[michaelmozina]

On a clear, moonless night in Mt. Shasta, you might see 6100. Ah the joys of not living in a big city. <img src="/images/icons/smile.gif" /><br /><br />I guess a few of the variables would be light in the vicinity, field of view, moonlight conditions, individual vision, etc. I can't really say I've spent the night counting stars I could see, and even then, my vision may not be nearly as good as it was in my 20's. Ok, maybe I'd only see 6000 now. <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> It seems to be a natural consequence of our points of view to assume that the whole of space is filled with electrons and flying electric ions of all kinds. - Kristian Birkeland </div>

 

[input22]

Actually the real count is:<br />New York: 0<br />Toronto: 8<br />Chicago: 2<br />Phoenix: 1,007<br />Athens: -2<br />Paris: 5<br /><br />etc., etc.

 

[derekmcd]

Good answer <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> <div> </div><br /><div><span style="color:#0000ff" class="Apple-style-span">"If something's hard to do, then it's not worth doing." - Homer Simpson</span></div> </div>