Paula Cleggett-Haleim
Headquarters, Washington, D.C.                      June 9, 1993
(Phone:  202/358-0883)            

Jim Elliott
Goddard Space Flight Center, Greenbelt, Md.
(Phone:  301/286-6256)

Ray Villard
Space Telescope Science Institute, Baltimore, Md.
(Phone:  410/338-4514)

RELEASE:  93-108

HUBBLE CLOSING IN ON AGE OF THE UNIVERSE

     Astronomers working with NASA's Hubble Space Telescope today
announced results of a major step to measure the Hubble Constant
and the age of the universe.

     The team has discovered Cepheid (variable) stars in its
first target, the spiral galaxy M81, and measured the distance of
the galaxy to be 11 million light years.  They quote a 10 percent
uncertainty in this result (plus or minus approximately one
million light years).  Previous estimates of the galaxy's
distance have ranged from 4.5 to 18 million light years.

     Cepheids are pulsating stars that become alternately
brighter and fainter with periods ranging from 10 to 50 days.
Astronomers have known for over 50 years that the periods of
these stars precisely predict their total luminous power, which
allows their distance to be measured.

     The Hubble Constant (H0) is the ratio of the recession
velocities of galaxies to their distances in the expanding
universe.  The age of the universe can be estimated from the
Hubble Constant and currently is thought to lie between 10 and 20
billion years.  A more precise measurement of the Hubble Constant
is required to narrow this range.

     Team member Dr. Wendy Freedman of Carnegie Institution of
Washington said, "In our two observed fields in M81, we have
found a total of 32 Cepheids.  Decades of previous work from the
largest ground-based telescopes have only succeeded in measuring
periods for two Cepheids.  HST's superior resolution and its
ability to schedule observations when and where they are required
give HST a special advantage in this work."

     Messier 81 is a large spiral galaxy in the constellation
Ursa Major.  It is a rotating system of gas and stars similar to
the Milky Way galaxy, but approximately twice as massive.  This
galaxy achieved prominence 3 months ago when the brightest
northern supernova of this century was discovered.

     The astronomers used the Hubble's Wide Field & Planetary
Camera to study two fields in M81.  In each field they took 22
20-minute exposures spread over 14 months to find the variable
stars and measure their periods and brightness.

      The project is one of several so-called "key projects"
designated top priority scientific goals for the Hubble Space
Telescope.  This extragalactic distance scale key project aims to
discover Cepheids and measure the distances to galaxies to
determine an accurate value of the Hubble Constant.

      Dr. Jeremy Mould, Principal Investigator for the team,
said, "This is the first step in a major program of measuring
distances of galaxies with the Hubble Space Telescope.  When the
telescope is serviced later this year, and the new Wide Field &
Planetary Camera is installed with its corrective optics, we plan
to use the same technique on galaxies up to 50 million light
years away, which will allow us to measure the Hubble Constant,
the rate of expansion of the universe.

      "We have 3 years of work ahead of us and, until the project
is substantially complete, I won't speculate on what value of H0
this work will yield."

      Although this HST key project has the explicit goal of
getting H0, other astronomers have used Hubble to search for
Cepheids.  Previous HST observations carried out by a different
group also demonstrated HST's unique capability by resolving 27
Cepheids in another galaxy.

      The announcement was made at the 182nd meeting of the
American Astronomical Society in Berkeley, Calif.  The results
are detailed in several presentations by team members at that
meeting and are being submitted for publication in the
Astrophysical Journal.

      The team, led by Jeremy Mould (California Institute of
Technology, Pasadena, Calif.), consisted of Sandra Faber and
Garth Illingworth (Univ. of California, Santa Cruz);  Wendy
Freedman, John Graham and Robert Hill (Carnegie Institution of
Washington);  John Hoessel (Univ. of Wisconsin, Madison);  John
Huchra (Center for Astrophysics, Cambridge, Mass.);  Shaun Hughes
(Caltech) (Univ. of Calif., Santa Cruz);  Robert Kennicutt (Univ.
of Arizona, Tuscon);  Myung Gyoon Lee (Carnegie);  Barry Madore
(Caltech);  Peter Stetson (Dominion Astrophysical Observatory,
Victoria, British, Columbia);  Anne Turner (Univ. Arizona,
Tuscon); and Laura Ferrarese and Holland Ford (Space Telescope
Science Institute, Baltimore).

- end -
     ___    _____     ___
    /_ /|  /____/ \  /_ /|     Ron Baalke         | baalke@kelvin.jpl.nasa.gov
    | | | |  __ \ /| | | |     Jet Propulsion Lab |
 ___| | | | |__) |/  | | |__   M/S 525-3684 Telos | The tuatara, a lizard-like
/___| | | |  ___/    | |/__ /| Pasadena, CA 91109 | reptile from New Zealand,
|_____|/  |_|/       |_____|/                     | has three eyes.