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© Anthony Ayiomamitis
This Friday night, if you think the Moon looks unusually big, you're right. It's the biggest full Moon of 2010. Astronomers call it 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 but 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 through Saturday morning: diagram.

A good time to look is Friday 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. Why not let the "Moon illusion" amplify a full Moon that's extra-big to begin with? The swollen orb rising in the east may seem close enough to touch.