NOTE:  The U.Va. department of astronomy is co-sponsoring two
comet-viewing nights in the area.  The first, on Wednesday, March 26,
will take place at the Ivy Creek Natural Area from 7 p.m. to 9 p.m.
On Tuesday, April 1, viewers are invited to gather at Meriwether Lewis
Elementary School on Owensville Road near Ivy from 7 p.m. to 10 p.m.

A SUBLIME ENCOUNTER:  COMET HALE-BOPP
COMES TO CHARLOTTESVILLE

	CHARLOTTESVILLE, Va., March 13 -- Already a bright spot in the
early morning sky, Comet Hale-Bopp will continue to dazzle viewers
throughout March and April.  This cosmic visitor, dubbed the Comet of
the Century, is certainly the most massive comet to visit the inner
solar system since the great comet of 1811, which presaged Napoleon's
defeat in Russia and which Tolstoy describes in "War and Peace," says
astronomer Al Wootten.  Indeed, Wootten adds, Comet Hale-Bopp will
probably be the "greatest comet to visit since Tycho Brahe's great
comet of 1577, a time before the invention of telescopes." (Brahe was
a Danish astronomer whose careful observations over several decades in
the mid- and late 1500's enabled him to chart the positions of 777
stars.)
	Named for its discoverers, amateur astronomers Alan Hale and
Thomas Bopp, the comet, whose formal name is C/1995 O1, will pass
within 194 million kilometers (120 million miles) of the Earth on the
night of March 23.  At its brightest, the comet may be as bright as 0
to -1.5 magnitudes.  Magnitude is a measure of brightness based on the
brightest star in the Northern Hemisphere, Vega, which is defined as
being zero magnitude.  Objects brighter than Vega are placed on the
negative side of the scale.  Unlike many celestial objects, Comet
Hale-Bopp is best viewed without a telescope.  During the comet's peak
brightness in March and April, viewers need only travel away from
bright city lights and look towards the northwest sky any time after
sunset.
	Wootten, an astronomer at the National Radio Astronomy
Observatory in Charlottesville, is studying Comet Hale-Bopp with both
the 43-meter telescope in Green Bank, W.Va., and the 12 meter
telescope in Tuscon, Ariz.  Wootten looks at the comet's "coma" -- the
aura of dust and gas that surrounds the dense, icy heart of the comet
and that may reach 100,000 kilometers in diameter as the comet moves
ever closer to the sun. 
	"The most abundant gaseous constituent of a comet is water,
which is in the form of ice in the outer solar system," says Wootten.
As the comet approaches the sun, the water sublimes -- passes directly
from a solid to a gaseous state.  Because there is so much water vapor
in earth's atmosphere, astronomers cannot directly measure water vapor
of the comet's coma with earth based telescopes.  Instead, Wootten and
his co-workers look for the hydroxyl molecules that are formed as
ultraviolet light from the sun splits water into its constitutents, a
hydroxyl group (OH) and a hydrogen (H) atom.  With this information,
the scientists hope to determine the rate of water sublimation.  "At
the 12-meter telescope in Tuscon, we are measuring methanol (wood
alcohol) and formaldehyde emission.  In addition to measuring the
amounts of these trace constitutents of the coma, we are using their
emissions to measure the coma's temperature -- particularly the radial
structure of the temperature distribution, which has not been measured
previously," says Wootten.
	###

March 12, 1997
	REPORTERS:  Contact Al Wootten (after March 20) at NRAO at
(804) 296-0329 or awootten@nrao.edu.

	Contact the Ivy Creek Natural Area at (804) 973-7772.

	For general information about comets, contact Charlie Tolbert
in the U.Va. astronomy department at (804) 924-7494 or
crt@virginia.edu.

	Website for more information and images of Comet Hale-Bopp is
http://encke.jpl.nasa.gov/index.html.

	Television reporters should call our TV News Office at (804)
924-7550.