Monday, May 4, 2020

Venus

I rolled Big Bertha out a couple nights ago and looked at Venus, that really bright "star" in the west in early evening.  This is the only time that I have seen it at crescent phase.  Venus' phases were a surprise to Galileo.  If Earth was at the center of the solar system, these phases were impossible.

1 comment:

Karl said...

Actually, phases aren't themselves impossible if the Earth is at the center of the solar system. All that's needed is for the Sun to be in an orbit farther from the Earth than Venus is.
However, the pattern of the phases, and retrograde motion of Venus and Mercury, work so much better if you assume those planets orbit around the Sun.

Even then, all you need is a coordinate transform to put Earth at the center of your reference frame. But then orbital mechanics becomes a lot trickier.