Q: Why can we sometimes see the moon in the daytime?

A: The moon takes about four weeks to complete its orbit around Earth, said Jim Lattis, director of Space Place, a UW-Madison outreach project on South Park Street. When the lunar month begins - the new moon is located sunward of Earth, and it is invisible.

As the moon moves east over a couple of days, a thin, faint crescent moon may appear in the western sky just after sunset. Several nights later, the moon is fuller, brighter and higher in the sky at any time of day, all of which make it more obvious against the bright blue sky.

As the moon continues to move east, it fattens toward a full moon, becoming brighter and more visible in the afternoon. The full moon rises when the sun sets and is directly opposite the sun in the sky. After full moon, the moon is not visible in the afternoon, but it will appear in the morning, first as nearly full, then as a shrinking crescent.

Toward the end of the lunar month, the crescent dwindles to nothing as the moon once again rises with the sun, and we are back to new moon.

Produced in cooperation with University Communications

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