Astronomy Picture of the Day

Discover the cosmos! Each day a different image or photograph of our fascinating universe is featured, along with a brief explanation written by a professional astronomer.

April 19, 1999
See Explanation.  Clicking on the picture will download 
 the highest resolution version available.

The Full Moon
Credit: Lick Observatory

Explanation: Earth has one moon. A symbol in famous love songs, movies, poems, and folklore, many myths about the Moon date back to ancient history. In fact, the name Monday originates from Moon-day. The Moon glows by light it reflects from the Sun and is frequently the brightest object in the night sky. The Moon orbits the Earth about once a month (moon-th) from about 1 light second away. The above-pictured Full Moon occurs when the Moon is nearly opposite to the Sun in its orbit. The Moon's diameter is about 1/4 that of the Earth, and from the Earth's surface appears to have almost exactly the same angular size as the Sun. Recent evidence indicates that the Moon formed from a colossal impact on the Earth about 4.5 billions of years ago, and therefore has a similar composition to the Earth. Humans walked on the Moon for the first time in 1969.

Tomorrow's picture: Big Boom

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Authors & editors: Robert Nemiroff (MTU) & Jerry Bonnell (USRA)
NASA Technical Rep.: Jay Norris. Specific rights apply.
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& Michigan Tech. U.