Sky and Telescope
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| The Ulysses spacecraft is about halfway through its pass
above the Sun's south pole. Sky & Telescope diagram; courtesy
European Space Agency. |
Today the Ulysses
spacecraft has come its closest to being directly over the Sun's
south pole. The craft's solar southern latitude is now 80.1°,
though Ulysses is still quite far from the Sun (344 million kilometers,
or 2.3 astronomical units). Even so, from this perspective the nine
instruments aboard are immersed in a heliospheric environment that
cannot be experienced closer to the planetary plane. Ulysses is
making its second swing over the southern pole, the first coming
in September 1994. At that time the Sun was much less active, and
its polar winds escaped easily without having to encounter much
magnetic turbulence. "This time around, Ulysses has not seen
the fast solar-wind streams that were typical of the polar regions
at solar minimum," notes project scientist Richard Marsden.
The current winds are averaging 600 km per second, versus the 750
km per second often observed during the 1994 pass.
Built by the
European Space Agency, Ulysses was launched toward Jupiter in
October 1990. Its close flyby of the giant planet in February
1992 changed its orbit drastically, throwing the craft back toward
the Sun in a looping, polar orbit. Following this month's south-polar
pass, the spacecraft will swing back up through the ecliptic plane
and cross over the northern pole next October. By then the Sun's
magnetic field should have switched polarity, an event that Marsden's
team is very much looking forward to monitoring.
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