astronomylight-pollutionobservers
I have always lived near a large city. There is a stark contrast between the picture linked below for example, and what I see with the naked eye.
Sometimes I can see a few stars here and there, but usually they can be counted on my fingers. I'm looking up at the night sky right now, and there isn't a single visible star!
Question: What creates this large gap in what I can see?
Here's the photograph I was talking about: http://apod.nasa.gov/apod/ap120123.html
The number of stars that are visible depends heavily on local conditions. Under perfect conditions (e.g. a mountain area with minimal atmospheric turbulence) and with perfect eyesight, one would be able see stars as faint as magnitude 6.5. Of course, conditions are usually not ideal. According to this site, there are
1500 stars brighter than mag 5.0
4800 stars brighter than mag 6.0
6000 stars brighter than mag 6.3
8000 stars brighter than mag 6.5
in the entire night sky. Of course, at any given moment you can only see half of the celestial sphere. But as the Earth rotates, you can observe a larger portion of the night sky from a given location: for example, someone on the equator can in fact observe the entire night sky. It's easy to show that someone on a latitude $\varphi$ can observe a fraction $\frac{1}{2}(1 + \cos\varphi)$ of the celestial sphere. Someone in the Mediterranean can see ~90%, while someone in central Europe can see ~80% over the course of a year.
However, there are a few factors that limit the number of stars that we can actually see with the naked eye. First, it's more difficult to see stars near the horizon than stars near the zenith, because the former have to pass through more air mass. So the threshold magnitude depends on the altitude above the horizon. Second, many stars are components of binary systems (or multiple star systems). Of course, to the naked eye these systems appear as single stars.
So how many stars were known prior to the invention of the telescope? The standard star catalogue in the Middle Ages was the one published by Ptolemy in the 2nd century (part of his Almagest), which in turn was based on Hipparchus' work. Ptolemy's Almagest contains 1022 stars. In the Arab world, Ptolemy's work was updated by Al-Ṣūfī, who published his Book of the Fixed Stars in 964.
The first real improvement, particularly in positional accuracy, was made by Tycho Brahe, who completed his ”thousand-star” catalogue in 1598. His catalogue contains 965 stars. Finally, Johannes Hevelius published the last major catalogue based on naked eye observations in 1687, the Catalogus Stellarum Fixarum, which contains 1,564 stars. The gaps in the southern sky were filled by Louis de Lacaille, who sailed to South Africa in 1750, but his work is based on telescope observations.
It would be interesting to know how many stars were catalogued by Indian and Chinese astronomers, but I haven't found info on that.
Here is an update on (my) answer that your refer to. I have changed the visual threshold to V<6.5 mag (which is what Sky and Telescope have done) and I have used the revised Hipparcos reduction from van Leeuwen (2007) (catalogue available here) to obtain a (almost) complete catalogue of stars with their trigonometric parallaxes. It contains 7892 stars. I am not going to investigate the discrepancy with the Sky and Telecope article which uses the Hoffleit & Jaschek bright star catalogue as their reference.
The distribution of distances is illustrated in the two plots below (labelled in light years, as you wish). The first shows the number of stars as a function of distance. The second shows the cumulative fraction of stars closer than some distance. From this, you can read off, or I can tell you, that 90% of bright stars in the Hipparcos catalogue are closer than 1175 light years.
NB: I don't think 4 significant figures are warranted. There are some tens of bright stars that are so distant that their parallaxes are too small and are garbage (negative in some cases). I'm also not clear about what the status of binary stars are (you can't resolve them, but in many cases Hipparcos could)
Number of bright stars versus distance
Normalised cumulative frequency of star distance
Best Answer
This is a simple and clear issue, with a unique answer. I see other replies mentioning weather conditions, dark adaptation and so on. That's just so much hand waving, given that the first thing you said was "I've always lived in somewhat large cities".
The core problem here, by a very wide margin, is light pollution if you live in a large city. This is the one factor, above everything else, that affects your ability to see the stars.
Here's a light pollution map:
http://www.jshine.net/astronomy/dark_sky/
The white zones are the worst, and they are in the middle of the cities. Black zones are the best.
Here's a somewhat better (but not perfect) comparison of a dark sky versus light polluted sky (your picture was taken with a very long exposure that doesn't look very realistic):
The dome of light above the city is very visible if imaged from afar:
Long exposure pictures in cities will reveal the orange skyglow, which is the main reason why you can't see the stars - it's like noise masking off the faint light from the distant objects:
Light pollution affects primarily the observations of faint objects, such as nebulae or distant galaxies. Bright objects such as the Moon, the big planets, or some of the bright stars, are not affected by light pollution.
Using a telescope with a large aperture alleviates the effects of light pollution to some extent, but it cannot work miracles. A dark sky is always better.
Usually a 1 hour drive away from the city will bring you in a place with dark sky, free of light pollution - but it depends on several factors. In such a place you should be able to see the Milky Way with your naked eye. The Andromeda galaxy also is visible with the naked eye if the sky is dark enough.