How big( in relation to the horizon )does a harvest moon get?

Question

I saw the moon in Jamul, California get so big once there was very little sky showing. It also went through many color changes. Silver. Silver in the center with gold edges. Then a hazy overall yellow. Then pure 24k gold. Then a purple tinged with green. Back to Gold. Back to silver. Is this a common phenomenon?

Answer 1

The full moon has an angular size of 0.5 degrees, plus or minus a tiny bit, whether it is on the horizon or well above it. Our visual senses interpret images at low elevations differently than at high ones. It is a trick that is played in our brains, not the sky.
Near the horizon there is much more air for the light to pass through because of the angle than the more direct path from higher angles of elevation. As a result, all the pollution, turbulence, and so forth have a greater effect than at higher angles. The longer path also filters out the higher frequency colors of the spectrum with the moon just as it does with the sun. The moon becomes more 'white' at higher angles.
The color changes that you mention seem a bit extreme, but parts of California are famous for pollution, so I guess that anything is possible.
FYI I have measured the size of the moon at both low and high angles with accurate instruments because I had to prove the size thing for myself.

Answer 2

The horizon subtends 360 degrees. The moon is about half a degree across. Hence, it would take 720 moons (approximately) to extend all the way around the horizon, side by side.

The size of the moon DOES change, both because it's orbit is not a circle, and because it is 4,000 miles (roughly--it's really one earth radius) closer when it is directly overhead versus when it is rising or setting. If it is at its perigee and overhead it is several per cent larger than at apogee and on the horizon. Still, the difference is too small to see without optical or photographic assistance.

Answer 3

Ahem....the moon doesn't change size.