I was talking with a friend about how slowly the star field changes (based on the speed that we are moving through the galaxy) and I started to wonder about a star's visible size. They are basically the pixels that make up our sky. This made me wonder, how many stars (let's use the north star as a reference.) would it take (lined up side by side) to draw line that appeared solid across the middle of the sky, perpendicular to the horizon which appeared solid?
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2$\begingroup$ I never would have thought there would be a way to ask "how many pixels does the sky have?" and get away with it, but you pulled it off! $\endgroup$ – uhoh Jul 19 '16 at 4:44
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$\begingroup$ The milky way is pretty much solid, just not a thin line but a wider band (and not of uniform luminosity). $\endgroup$ – orion Jul 19 '16 at 6:28
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This is more of a question of human perception, than astronomy. I was going to answer your question with this: "One, it just needs to be close to Earth." But, I decided it wasn't THAT funny. Anyway, stars are essentially point sources as far as our eyes are concerned. Typical visual resolution is about 0.02° or 0.0003 radians. Assuming from horizon to horizon is 180° (or π radians) that calculates out to roughly 10,000 stars. I'd probably increase that by 50% or 100% to be sure. You do understand that you can't line stars up side by side, I hope. There's no need, its about the angular distance, not absolute distance between them, that matters. They can be light years apart as long as they appear to be within about 1 arcminute of one another, our eyes will see them as a single object - subject to the psychological aspects of keeping color and apparent magnitude roughly uniform as well.
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2$\begingroup$ This was going to be my answer, but I have been beat! $\endgroup$ – Tanenthor Jul 19 '16 at 4:17
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1$\begingroup$ I'll vote +1 for "funny" because you were nice enough to continue and leave a remarkably well thought out answer as well! Speaking of pixels, just a factoid for comparison, if a phone has 400 pixes/inch and it's 16 inches from my face, that's about half, or 0.00016 radians and considered below visual resolution. $\endgroup$ – uhoh Jul 19 '16 at 4:40
