Rani Gran
Goddard Space Flight Center, Greenbelt, Md. January 12, 2007

Comet McNaught -- A First Light Present for STEREO

This image
[http://www.nasa.gov/images/content/1...naught_lg.jpg] of
Comet McNaught comes from the Heliospheric Imager on one of the STEREO
spacecraft, taken Jan. 11, 2007. To the right is the comet nucleus, so
bright it saturates the detector creating a bright vertical band in the
image. The comet's dynamic tails extend up and to the left.

The lowest of the tails is the ion tail, which points along the direction of
the solar wind. Above that is the comet's dust tail pushed out by radiation
pressure from the sun. The tail is highly structured, probably the result of
dynamic activity in the comet itself.

Although the two STEREO observatories have been turning on their instruments
since mid-December, the Heliospheric Imagers on this spacecraft turned on
for the first time on Jan. 11 -- just in time to see the spectacular Comet
McNaught.

The Heliospheric Imagers are designed to observe the space between the Sun
and the Earth in order to watch solar storms as they head our way. But here
the Heliospheric Imagers are also able to observe Comet McNaught as it heads
towards the sun.

STEREO's SECCHI/HI instrument was built by a consortium led by the Naval
Research Laboratory (USA), and includes the University of Birmingham (UK),
Rutherford Appleton Laboratory (UK) and Centre Spatiale de Liege (Belgium).

Image credit: NASA