SOHO prepares for comet McNaught (Forwarded)

ESA News
http://www.esa.int

11 January 2007

SOHO prepares for comet McNaught

Recently, sky watchers in the Northern Hemisphere have been enjoying the
sight of Comet McNaught in the twilight sky. Now, solar physicists using
the ESA-NASA SOHO spacecraft are getting ready for their view. For four
days in January, the comet will pass through SOHO's line of sight and
could be the brightest comet SOHO has ever seen.

As Comet McNaught heads towards its closest approach to the Sun on 12
January 2007, it will disappear from view for earthbound observers,
becoming lost in the Sun's glare. That's where SOHO comes in. Poised in
space between the Earth and Sun, SOHO ceaselessly watches the Sun and
objects that pass nearby.

Comet McNaught will pass within a fifth of the distance between the Earth
and the Sun. As the comet approaches the Sun, the amount of dust and gas
it releases will increase dramatically, causing the comet to become
extremely bright. "This might become the brightest comet SOHO has ever
seen," says Bernhard Fleck, SOHO Project Scientist.

The material ejected from the comet forms the tails. There are two tails,
the dust tail and the gas -- or ion -- tail. The dust tail is the brighter
and is formed by the intense sunlight forcing dust particles away from the
comet. The solar wind, a constant stream of material flowing from the Sun,
drags ionized gas from the comet to create the ion-tail.

Researchers Karl Battams and Jeff Morrill at the Naval Research Laboratory
in Washington, DC are planning colour filter observations of these two
comet tails. "Close to the Sun the ion and dust tails move apart, a
phenomenon that is often difficult to observe from the Earth. By measuring
the ion-tail angle we can get information about the solar wind speed very
close to the Sun," says Morrill.

Comet McNaught is moving through space on an inclined orbit. This will
carry it above the Sun's north pole and across the Sun's equator, a place
where there is a reversal of the magnetic properties of the solar wind.
Crossing this boundary could cause the comet's ion-tail to fragment.
Observations of such events are generally very rare, so SOHO's images of
comet McNaught constitute an exciting opportunity for scientists.

After SOHO's work is finished, the comet will emerge from the Sun's glare
and become visible again to earthbound sky watchers in the Southern
Hemisphere. "It could become a really bright object in the twilight sky,"
says Fleck. The ghostly veils of a bright comet are amongst the most
spectacular of sights that can be seen in the night sky.

Between 12 and 15 January, Comet McNaught will not be visible from Earth
but everyone can still track the comet's passage near the Sun by looking
at the SOHO images at
http://soho.esac.esa.int/hotshots/

For more information

Bernhard Fleck, ESA SOHO Project Scientist
Email: bfleck @ esa.nascom.nasa.gov

Daniel Müller, ESA SOHO Deputy Project Scientist
Email: dmueller @ esa.nascom.nasa.gov

Karl Battams, Naval Research Laboratory, Washington DC, USA
Email: karl.battams @ nrl.navy.mil

Jeff Murrill, Naval Research Laboratory, Washington DC, USA
Email: morrill @ shogun.nrl.navy.mil

[NOTE: Images supporting this release are available at
http://www.esa.int/esaSC/SEMMCRSVYVE_index_1.html ]

More about ...

* SOHO overview
http://www.esa.int/esaSC/120373_index_0_m.html

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Related links

* Comet McNaught photo gallery
http://www.spaceweather.com/comets/gallery_mcnaught.htm
* SOHO comets page
http://ares.nrl.navy.mil/sungrazer/
* SOHO comets movies
http://soho.nascom.nasa.gov/gallery/Movies/comets.html
* SOHO hotshots
http://soho.esac.esa.int/hotshots/