Astronomy Picture of the Day

A Tail of Two Hemispheres

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#98602 by @ 02.02.2007 00:00 - nach oben -
A Tail of Two Hemispheres


By January 19/20 Comet McNaught's
magnificent dust tail stretched
for about 150 million kilometers (~1 AU), requiring images from both
southern and
northern hemispheres of planet Earth
to take it all in.

Two such views - from
Cerro Paranal in Chile (left)
and the Carnic Alps in Italy - are
combined in this unique
that also outlines
a perspective view of the comet's orbit (dotted line) and
relative position of the Sun.

Driven by
solar radiation pressure the dust tail initially
points away from the Sun, but also trails outside the comet's

Astronomers try to
for the complex structure along the tail,
including the pronounced striations, by
considering forces acting on
the dust (e.g. gravity,
solar wind
and radiation) as well as the
release time and size of the
dust grains.

In the diagram, the modeled location of dust grains released
at approximately the same time relative to
passage, synchrones, are shown as dashed lines.

The location of grains of similar size, syndynes, are shown as
solid lines.

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