Once while well-known astronomy lecturer and author by George Lovi (1939-1993) was running a public night at the Brooklyn College Observatory in New York, the telescope was pointed at Venus, displaying a delicate crescent shape. Yes, Venus goes through phases, just like the Moon does, as seen from our point of view.

A student, surprised by the crescent, stubbornly insisted he was really looking at the Moon. Lovi pointed out that the Moon wasn't even in the sky that night.

"So what?" the student said. "Doesn't a telescope show you things you can't see without it?"

This is but one of a number of popular misconceptions in astronomy. Some are widely held, others linger more as confounding questions in the backs of peoples' minds. Why don't meteor showers actually rain down? Is there a South Star? Why is July so hot?

Here's my own personal list of ten Confounding Cosmic Questions, in no particular order, along with some less confounding answers:

1

Is a half Moon half as bright as a Full Moon?

It is certainly logical to expect that when the Moon is 50 percent illuminated (at First or Last Quarter phase; also sometimes called the "half-moon"), that it would be shining only half as bright as a Full Moon.

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Indeed, if the Moon's disk was flat like a white piece of paper or a projection screen, then its surface brightness would be the same all over and this would be true.

But of course, this is not the case. The Moon is a sphere, and the amount of reflected light from the Sun per unit of Moon area decreases toward the lunar terminator (the dividing line between the bright and shaded regions). Near and especially along the terminator, mountains and boulders strewn across the lunar landscape cast innumerable shadows. This gives the effect of the Moon appearing brightest near and along its edge, but grayer toward the terminator.

In contrast, at Full Moon, the Sun is shining on the Moon from nearly the same direction as we are viewing from the Earth. That is, the Sun is behind us as we view the Moon. (It is directly behind during a total lunar eclipse.) This means that all the shadows cast by mountains on the Moon are directly behind the objects casting them -- and thus are not visible to us.

Believe it or not, only about 2.4 days from Full Moon does the Moon shine half as bright as when it's full. And when the Moon is at First Quarter phase, it is actually only 1/11 as bright as full!

At Last Quarter it's even dimmer - 1/12 - because of the greater visible area of the dark maria (or lunar "seas") on its illuminated portion. [See our Skywatcher's Guide to the Moon]

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