NASA'S HUBBLE SPACE TELESCOPE ESTABLISHES
       ACCURATE NEW DISTANCE MEASUREMENT TO NEIGHBORING GALAXY

Recent observations of the remnants  of  Supernova  1987A,  conducted
with NASA's Hubble Space Telescope, have provided an unexpected bonus
-  an  accurate  determination  of the absolute distance to the Large
Magellanic Cloud, a satellite galaxy of the Milky Way, located in the
southern hemisphere.

The refined value of 166,000 light-years is accurate to  within  five
percent  say  the researchers.  Previous estimates range from 160,000
to 195,000 light-years. This new measurement is a cornerstone for the
determination of the size and the age of the Universe.

These findings were reported today at the  meeting  of  the  American
Astronomical    Society   in   Philadelphia,   Pennsylvania   by   an
international team of astronomers: Nino Panagia, Roberto Gilmozzi and
F. Duccio Macchetto, ESA astronomers at the Space  Telescope  Science
Institute  in Baltimore, Dr. Hans-Martin Adorf of the Space Telescope
European Coordinating Facility in Garching, Germany, and  Dr.  Robert
P.  Kirshner  of  the  Harvard Smithsonian Center for Astrophysics in
Cambridge.

"This is an achievement of great importance because the  distance  to
the Large Magellanic Cloud is an essential step to the calibration of
the  cosmological  distance  scale, " says Panagia. "Therefore, being
able to determine this distance with an accuracy  of  5%  means  that
after  a  few  more  comparable steps we will be able to estimate the
Hubble constant (the distance scale of the universe) to  an  accuracy
of  10-15%  and, therefore, the age of the Universe with that high an
accuracy as well."

These results are based on observations made with the European  Space
Agency's  Faint Object Camera (FOC) last August. The FOC revealed for
the first time the  detailed  structure  of  an  eerie  gaseous  ring
surrounding  the  remnants  of  supernova  1987A,  which  exploded on
February 23, 1987 in the Large Magellanic Cloud.

This ring is a relic of the nitrogen enriched stellar  envelope  that
was  ejected  in  the  form  of a stellar wind by the progenitor star
when it was in the phase of red supergiant.  The material  was  later
compressed by a fast wind from the star when it had evolved back to a
blue supergiant state, just a few thousand years before the explosion
occurred.    The  stellar  wind  was  apparently  more  efficient  at
compressing gas along an  equatorial  belt  to  produce  a  ring-like
rather than shell-like structure.

"Thanks  to the FOC observations" says Nino Panagia, "we know that we
are dealing with a real ring which is an equatorial structure.  HST's
ability to resolve the ring  structure  has  allowed  astronomers  to
accurately  measure  its  angular  diameter  which  is the first step
toward  estimating  the  supernova's  true  distance.    HST's   high
resolution  unequivically shows that ring has angular diameter of 1.7
arcseconds, which is equivalent to the apparent separation between  a
pair of car headlights located 100 miles away.

Once  aware  of  the  ring  structure,  the  astronomers were able to
estimate the ring's physical diameter, which is the  second  step  in
calculating  its  true distance.  This required analyzing three years
worth  of   SN1987A   ultraviolet   data   gathered   by   NASA/ESA's
International  Ultraviolet  Explorer  (IUE) satellite. The data are a
record of how ultraviolet emissions  from  the  ring  brightened  and
dimmed following the 1987 explosion.

Since  the  ring  is inclined along the line-of-sight, light from the
full circumference of  the  ring  didn't  reach  Earth  at  the  same
instant.  Light from the edge of the ring tilted toward Earth reached
the IUE 80 days after the supernova.  Light form the edge of the ring
tilted farthest away from Earth didn't arrive until  420  days  after
the  explosion.   This  time  difference  allows  the  researchers to
accurately calculate the ring's physical diameter of 1.4 light-years.

With precise values for angular size and physical diameter  in  hand,
determination  of  true distance of 166,000 light-years is simple and
straightforward trignometric calculation.

The supernova ring has also provided new insights into the  evolution
of  a  massive  star.   By comparing the present diameter of the ring
and its expansion velocity, (as  determined  from  observations  made
with   IUE   as   well  as  ground-based  optical  measurements)  the
researchers infer that about 5000 years ago the star turned back to a
blue supergiant after being a red supergiant for  more  than  half  a
million  years.  "These are direct measurements of evolutionary times
for an individual star" Panagia emphasizes. "This  result  has  never
been obtained before in any other case on time scales so diverse".

In  the  years  to  come  HST will accurately measure the distance to
nearby galaxies,  ten  to  twenty  million  light  years  away.   The
ultimate  goal  is  to  measure  the  size  of  the  universe and, by
inference, determine its age, now estimated to be between 10  and  20
billion years.
                               *******

The  Space  Telescope  Science  Institute  is  operated  by AURA (the
Association of Universities for Research  in  Astronomy,  Inc.),  for
NASA, under contract with the Goddard Space Flight Center, Greenbelt,
Md.  The  Hubble  Space  Telescope  is  a  project  of  international
cooperation between NASA and ESA (the European Space Agency).