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Twelve Days of Mercury This Christmas

An excellent opportunity arises over the Christmas period for a rare view of the planet Mercury, just above the south-western horizon at dusk. Mercury will lie close to two other planets, brilliant Venus and gas-giant Jupiter, and they will all be joined by a crescent Moon on December 29th to form a spectacular grouping.

On Christmas Day, Mercury, the solar system's innermost planet, will shine at magnitude -0.7, about as bright as the brightest stars, while both Jupiter and Venus will be brighter still. Mercury will reach greatest eastern elongation, that is, greatest angular distance from the Sun, on January 4th. By January 9th, Mercury will have faded slightly as it continues in its orbit around the Sun.

Crater-surfaced Mercury has been in the news lately, as the NASA spacecraft Messenger has been skillfully imaging its uncharted surface. Messenger was launched in August 2004, and made flybys of Mercury in January and October this year, sending many photographs back to receivers on Earth for study by planetary scientists. The next flyby of Mercury is scheduled for September 2009, before the craft is placed into science orbit around Mercury for one year of intensive studies.

Highly accurate topographical measurements of Mercury will be made with Messenger's onboard laser altimeter, and its magnetometer and spectrometer will map Mercury's magnetic field structures and the abundances and radioactivity of the elements making up its surface.

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Last Revised: 2009 January 5th
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