topsie (12:20 pm):

the apparent size of the rising or setting sun or full moon when it is just above the horizon isn't just an illusion caused by it's proximity to the trees and rooftops, as many 'experts' claim, but is caused by magnification when it is seen through the atmosphere near the horizon.

The same magnification is responsible for what's called the "ephemeris jump" (you can look that up) noticed mostly for a setting sun or moon. The sun/moon appears to approach the horizon at "normal rate" until what looks like about the last 5 degrees (where it "should" take about 20 minutes more to reach the horizon) but "plops" out of sight in a minute or less. The effect is especially visible when seen from an airplane at 20 or 30 kft altitude.

John