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S&T News Bulletin - May 5

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         SKY & TELESCOPE'S NEWS BULLETIN -- MAY 5, 1995
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NOT "MACHO" IN THE LMC

A 400-night imaging survey of the Large Magellanic Cloud (LMC) seems to
rule out another once-promising candidate for the dark matter thought to
comprise the bulk of our galaxy's halo.  Supposedly, massive compact halo
objects (MACHOs) are giant planets or tiny stars that exist in great
profusion around the galaxy's remote margins.  But over the past three
years Charles Alcock and his colleagues have been looked for them in the
center of the Large Magellanic Cloud using an Australian 1.3-meter
telescope -- with little success. The survey did record three otherwise
steady stars brightening and dimming over a few weeks' time, which matches
the predicted behavior of a star undergoing gravitational lensing by a
passing foreground MACHO.  Because the astronomers detected so few
candidate events, it would seem that MACHOs comprise at most 20 percent of
our galaxy's still poorly understood halo.  Indirectly, therefore, the
case has been strengthened for some exotic nonnuclear substance to make up
the bulk of the dark matter in our cosmic neighborhood.

SATURN's EDGE-ON RINGS

We're fast approaching the first of three nights this year when the
majestic rings of Saturn will be turned edge-on to us for the first time
since 1980 and thus rendered virtually invisible.  The first of the three
disappearances occurs May 21st, and right now the rings are tipped only
about 1/2 degree to our line of sight.  So if you observe Saturn right now
you're not likely to see much except the planet's distinctly flattened
ball.  Saturn rises only a few hours before dawn, so it's not particularly
well placed for viewing. If you have a good-size telescope you might try
to watch the planet's larger satellites play tag.  Tethys, Dione, Rhea,
and Titan are undergoing eclipses and occultations by Saturn and one
another.  A complete observing guide begins on page 68 of SKY &
TELESCOPE's May issue.

MERCURY IN THE EVENING

Mercury is in the midst of its best apparition of the year, but you'd
better act now to see it.  The illusive planet can be spotted about 10
degrees up in the west-northwest after sunset.  On May 12th the planet 
reaches its greatest eastern elongation from the Sun, though for us at
mid-northern latitudes the easiest spotting actually occurs two days
earlier -- weather permitting, of course.

A SPOTLESS SUN

Eagle-eyed observers report that the Sun has been virtually spotless since
April 22nd.  That's great if you're a dishwasher but not so hot if you're
a solar observer.  Even though we are approaching solar minimum, such a
spotless span is unusual.  When was the last time *you* saw any of these
dark blips on the Sun?

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   *------------------------------------------------------------*
   | Stuart Goldman         Internet: sgoldman@cfa.harvard.edu  |
   * Associate Editor                 mrastro@aol.com           *
   | Sky & Telescope                                            |
   * P. O. Box 9111           Sky & Telescope: The Essential    *
   | Belmont, MA  02178           Magazine of Astronomy         |
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