Why does the Milky Way appear curved?

[mapguy]

Clear skies this weekend, so we drove 30 miles out of the city, and enjoyed a good view of the Milky Way. One thing that confused me, though: the band seemed to have a slight curve to it as I followed it across the sky. Since the plane of the galaxy is flat, I would've expected the Milky Way to appear as a straight line across the sky when viewed with the naked eye. Is there something about our atmosphere that causes it to refract into a curve? Or was I experiencing some kind of optical illusion, perhaps having to do with the curvature of the Earth?

[ngc3314]

The midplane of the Milky Way does appear very close to a great circle (as shown on celestial maps). In my experience, the eye doesn't do a very good job of telling us that - my worst example is seeing the phase of the Moon with the Sun in the sky. I know perfectly well that the crescent must point exactly along a great circle to the Sun, but my perception is pretty much always that it angles one way or the other.

When the Milky Way goes exactly overhead, I do see it as a great circle, when the visual perception is pretty much "that's vertical".

[utesfan100]

Clear skies this weekend, so we drove 30 miles out of the city, and enjoyed a good view of the Milky Way. One thing that confused me, though: the band seemed to have a slight curve to it as I followed it across the sky. Since the plane of the galaxy is flat, I would've expected the Milky Way to appear as a straight line across the sky when viewed with the naked eye. Is there something about our atmosphere that causes it to refract into a curve? Or was I experiencing some kind of optical illusion, perhaps having to do with the curvature of the Earth?

A simple way to rule out an optical illusion would have been to hold up a straight edge to the Milky Way. If the Milky Way really was curved, the straight edge should appear as a tangent line to the curve.

Our brains tend to see the sky as a flat screen, rather than a spherical dome. I would expect the Milky Way to physiologically appear to curve away from you as you move your eye away from the highest point in the sky due to this effect, but a straight edge would show that it is indeed a line.

[John Mendenhall]

Plenty of obscuring dust, also. Wiki has good photos, article is 'Milky Way'.