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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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