[ut.stardate] Stardate jul 22

dipper@utastro.UUCP (Debbie Byrd) (07/29/84)

The planet Neptune will be carefully watched by some astronomers
today.  We'll tell you why -- right after this.

July 22  Occultation by Neptune

Today the planet Neptune gets special attention from astronomers
because today this faraway world passes in front of an
even-more-distant star, the faint star SAO186001.  This type of event
is called an occultation -- Neptune is said to occult the star.  In
this particular case, the occultation will be well observed -- because
Neptune is the only gas giant world in the outer solar system NOT known
to have a system of rings.

Saturn's rings have been known for centuries, since shortly after the
invention of the telescope.  Jupiter's ring or rings were discovered in
1979 by the Voyager spacecraft.  And the dark, narrow rings of Uranus
were discovered in 1977, in an event much like the one due to involve
Neptune and a star today.

When rings were discovered for Uranus -- just before Uranus was due to
occult a star -- astronomers saw the light from the star wink off, and
then return, several times before the main occultation.  What was
happening was just this -- the rings of Uranus were also passing in
front of the star, blocking its light.

Rings for Uranus and for Jupiter were a surprise.  Now it would almost
be a BIGGER surprise if Neptune doesn't have rings.  Then we'd have to
figure out why it doesn't, when all the other gas giants do.  In any
case, the issue will be resolved today only IF rings are discovered for
the planet Neptune.  Otherwise, we may have to wait until later in this
decade to find out -- sometime after the launch of Space Telescope --
or when Voyager finally gets to Neptune in 1989.

Script by Deborah Byrd.



(c) Copyright 1983, 1984 McDonald Observatory, University of Texas at Austin