Monday, February 14, 2011

Who's right? Mike Bara or every professional astronomer?

The Moon has an apogee of 405,696 km and a perigee of 384,399 km.
At apogee it has an angular diameter of 29.3 minutes — at perigee, 34.1'

Earth has an aphelion of 152,098,232 km and a perihelion of 147,098,290 km.
At aphelion, the Sun has an angular diameter of 31.6' — at perihelion, 32.7'.

Here's a sort of ASCII-graphics visual aid:
29         30         31         32         33         34 minutes of arc

(I realize that this could go seriously adrift for readers with non-standard browser settings, or who are reading this on their wristwatches.)

         For almost half its orbit, toward the apogee end, the Moon is apparently smaller than the Sun. For about a third of its orbit, toward the perigee, it appears larger. For the rest of the time the angular diameters of the two bodies are essentially identical. More competent people than you and me have found that rather amazing.

         So what does that mean for solar eclipses? Well, that depends on whether you are A) a trained astronomer or otherwise educated and sane person, or B) Mike Bara.

         If you're in Group A, you would say that when the Moon is in the apogee half of its orbit, a solar eclipse cannot ever reach totality because the apparent size of the Moon ain't enough to mask the Sun. Instead you have the rather spectacular effect of an annular eclipse.

         If you're in Group B, however, you would disagree. You'd say that an annular eclipse happens when the Moon is near perigee.

         Since Mike Bara's automatic response to any criticism of his writings and lectures is "I never said that," the question has to be, "Did Mike Bara write the following on page 214 of The Choice, or didn't he?

"An annular eclipse means that the Moon and Sun are in perfect alignment, but the Sun is not totally blotted out because the Moon is a little too close to the Earth."


Chris Lopes said...

So our favorite "engineer" isn't aware of the whole "the closer it is, the bigger it looks" idea? I'd have thought one of his porn star/stripper girlfriends would have pointed that out to him long ago. ;)

Biological_Unit said...

I think MB is correct on this one.

Chris Lopes said...


Maybe not.