Astronomy Picture of the Day

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

August 21, 1995

An Orbiting Iceberg
Credit: European Space Agency, Giotto Camera Team.

Explanation: A comet nucleus, formed from the primordial stuff of the solar system, resembles a very dirty iceberg. Orbiting far from our Sun, it can remain frozen, preserved for billions of years. Occasionally, a chance gravitational encounter will alter this distant orbit and send the nucleus plummeting towards the inner solar system. In 1986, the European spacecraft Giotto visited the nucleus of Halley's comet as it approached the sun. Data from Giotto's cameras were used to produce this enhanced image which shows surface features on the dark nucleus against the bright background of clouds of gasses produced as the icy material was vaporized by the Sun's heat. The potato shaped nucleus measures about 10 miles across.

Tomorrow's picture: Venus Unveiled

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