You might find this xkcd blog entry interesting, if you have not yet seen it: - Edit 1
Before modification by Joel at 15/02/2013 05:19:58 PM
It bears tangentially on this question:
Isaac already covered this pretty exhaustively, but consider 1) the naked eye can see many (though by no means all) stars from light years away and 2) they twinkle. Light pollution is often the biggest barrier: Obviously, few stars are visible by day beside Sol, and soon after acquiring my telescope I learned that whether one views the moon and planets or stars usually depends on whether the moon is nearly full or nearly dark; a full moon washes out much of the nearby sky, just like the sun. There is a reason naval ships have smoking lamps: Absent all other light sources, and perfectly skylined by the ocean, a lit cigarette is frequently visible all the way to the horizon.
I pause here, again tangentially, for my standard lunar observation warning: Telescopes with apertures >2-3" (5-8 cm ) should NOT on full or nearly full moons at low magnification. The quantity of light gathered and small surface area of exposed retina make the experience painful after 10-20 seconds, and dangerous after that.
3. If you were in a place that was completely flat, by which I mean a plane, not even on a curved surface such as the Earth, what limits would be placed on how far you could see? If there was nothing in your way, no buildings or anything, would you be able to see something big, say an Olympus Mons sized mountain, that was a thousand miles away? More? Or would dust, atmosphere, pollution, or whatever else combine to blur the sight of distant objects?
Isaac already covered this pretty exhaustively, but consider 1) the naked eye can see many (though by no means all) stars from light years away and 2) they twinkle. Light pollution is often the biggest barrier: Obviously, few stars are visible by day beside Sol, and soon after acquiring my telescope I learned that whether one views the moon and planets or stars usually depends on whether the moon is nearly full or nearly dark; a full moon washes out much of the nearby sky, just like the sun. There is a reason naval ships have smoking lamps: Absent all other light sources, and perfectly skylined by the ocean, a lit cigarette is frequently visible all the way to the horizon.
I pause here, again tangentially, for my standard lunar observation warning: Telescopes with apertures >2-3" (5-8 cm ) should NOT on full or nearly full moons at low magnification. The quantity of light gathered and small surface area of exposed retina make the experience painful after 10-20 seconds, and dangerous after that.