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About full Moon and Moon illusion

The size of a Full Moon depends on the position of the Moon in its orbit (~ 0.5 degrees). Thus the biggest Full Moon is when the Moon is closest to Earth (i.e. at perigee).

from spaceweather.com (28 Jan 2010)

“… a “perigee Moon” some 14% wider and 30% brighter than lesser full Moons of the year.

Johannes Kepler explained the phenomenon 400 years ago. The Moon’s orbit around Earth is not a circle; it is an ellipse, with one side 50,000 km closer to Earth than the other. Astronomers call the point of closest approach “perigee,” and that is where the Moon will be Friday night.

Look around sunset when the Moon is near the eastern horizon. At that time, illusion mixes with reality to produce a truly stunning view. For reasons not fully understood by psychologists, low-hanging Moons look unnaturally large when they beam through foreground objects such as buildings and trees.”

(Check also about Moon illusion on wikipedia.)

from APOD (25 Oct 2007)

“… The difference in apparent size between the largest and smallest Full Moon is quite dramatic and similar to this side by side comparison of the lunar apogee/perigee apparitions from 2006. But seen in the sky many months apart, the change is difficult to notice. “