Bad Astronomy: Misconceptions and Misuses Revealed, from ...

108 SKIES AT NIGHT ARE BIG AND BRIGHT
long, dark shaft. But we must be fair and look at the disadvantages
as well.
There is one big one, and it’s a deal-killer. Ironically, we looked
at it as an advantage before: the narrow opening of the chimney.
Before, it was good because it cut out glow from the sky, increasing
contrast, making it easier to see stars. However, the small
opening means there’s less of a chance of a bright star passing into
your field of view.
Most people think of the sky as being filled with stars. That’s
an illusion. You can see roughly 10,000 stars with the unaided eye,
and they’re spread out over the entire sky. We can estimate the
average number of stars you might see through the opening at the
top of a chimney. The answer may surprise you: even with a big
opening, you will usually see only about 10 to 20 stars on the very
darkest and clearest of nights. On a more typical night you might
only see one or two stars. So, actually, looking through a chimney
makes it a lot harder to see stars even at night. You are cutting out
so much of the sky that only a few stars can be seen through the
narrow aperture. During the day the odds are far, far worse. There
are only six objects that you can see during the day to start with,
not 10,000. The odds of one of these being in the chimney opening
are remote indeed.
Scientists, of course, don’t usually just calculate a number and
assume it’s correct. They actually go out and test it. An astronomer
named J. Allen Hynek did just that and published his results in an
issue of Sky and Telescope (no. 10 [1951]: 61). One day he took a
few members of his astronomy class to an abandoned smokestack
near Ohio University, where he taught. The bright star Vega—the
fourth brightest in the sky—passes very close to directly overhead
at that latitude, and they timed their experiment so that it would
be in their field of view from the bottom of the smokestack. Vega
is about half as bright as should be possible to see according to
our calculations, but it is still one of the brightest stars in the sky.
If it cannot be seen during the day, then certainly the vast majority
of stars cannot be seen then, either.
At the appointed time Hynek and his students peered upwards,
straining to see a glimmer from the star, but they all failed to observe