S&T's News Bulletin - Jun 23



New evidence strengthens the theory that our Moon was created during a
titanic impact of a Mars-size object with the Earth billions of years ago.
Using data gathered last year by the Clementine orbiter, planetary
scientist Paul Lucey and two colleagues have mapped the amount of iron
present in minerals all over the lunar landscape.  The percentage varies
>from  practically zero in the highlands to about 14% in the mare basins.
But these values are lower than would be expected if the Moon's
composition were the same as the Earth's mantle, so it now seems rather
unlikely that the Moon could have formed along with the Earth or was
somehow torn from its side.  Lucey's team also finds that huge areas on
the lunar far side have virtually no iron at all but instead consist of an
aluminum-rich silicate rock called anorthosite.  Pure anorthosite is rare
on the Earth, but it's exactly the kind of mineral expected to form a
crust if the whole exterior of the Moon were once a deep sea of molten
rock.  And such a magma ocean almost surely would have been present if the
Moon formed after a giant impact on Earth.


The Ulysses spacecraft has begun its exploration of the region over the
Sun's north pole.  It reached a solar latitude of +70 deg on June 19th and
will climb to +80 deg by the end of July.  The spacecraft passed over the
southern pole last year, where it found that the solar wind's velocity is
about 800 km per second -- roughly twice the speed of the wind coming from
equatorial regions.


The Space Shuttle's launch has been delayed at least one day, but that
won't affect your ability to watch the Mir space station as it coasts over
the U.S. in late June and early July.  Mir's passes over the U.S. and
southern Canada are depicted on page 69 of SKY & TEL's July issue, but
you'll need to make slight corrections to the lower map on that page.  In
general each pass should be shifted 5 millimeters in a direction
perpendicular to the track's length, toward the northeast. A time
correction must also be applied.  For observers near the U.S.-Canada
border, the spacecraft will come by about 30 minutes earlier than noted on
the map.  Those in the midsection of the U.S. will need to look about 20
minutes earlier, those in far-southern states about 12 minutes.  These
corrections are approximate; for an up-to-date list, see the SKY &
TELESCOPE postings on CompuServe in the GO SKYTEL areas, in the astronomy
area of America Online, or at Sky Publishing's new site on the World Wide
Web (http://www.skypub.com).

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   | Stuart Goldman         Internet: sgoldman@cfa.harvard.edu  |
   * Associate Editor                 mrastro@aol.com           *
   | Sky & Telescope                                            |
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