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PHOTO RELEASE NO.: STScI-PRC94-49c EMBARGOED UNTIL: 2:00 P.M. EDT
Wednesday, October 26, 1994

THE SPIRAL GALAXY M100

An image of the grand design of spiral galaxy M100 obtained with NASA's
Hubble Space Telescope resolves individual stars within the majestic spiral
arms. (These stars typically appeared blurred together when viewed with
ground-based telescopes.)

Hubble has the ability to resolve individual stars in other galaxies and
measure accurately the light from very faint stars. This makes space
telescope invaluable for identifying a rare class of pulsating stars, called
Cepheid Variable stars embedded within M100's spiral arms.

Cepheids are reliable cosmic distance mileposts. The interval it takes for
the Cepheid to complete one pulsation is a direct indication of the stars's
intrinsic brightness. This value can be used to make a precise
measurement of the galaxy's distance, which turns out to be 56 million
light-years.

M100 (100th object in the Messier catalog of non-stellar objects) is a
majestic face-on spiral galaxy. It is a rotating system of gas and stars,
similar to our own galaxy, the Milky Way. Hubble routinely can view
M100 with a level of clarity and sensitivity previously possible only for the
very few nearby galaxies that compose our "Local Group.''

M100 is a member of the huge Virgo cluster of an estimated 2,500
galaxies. The galaxy can be seen by amateur astronomers as a faint,
pinwheel-shaped object in the spring constellation Coma Berenices.

Technical Information:
The Hubble Space Telescope image was taken on December 31, 1993 with
the Wide Field Planetary Camera 2 (WFPC 2). This color picture is a
composite of several images taken in different colors of light. Blue
corresponds to regions containing hot newborn stars.

The Wide Field and Planetary Camera 2 was developed by the Jet
Propulsion Laboratory (JPL) and managed by the Goddard Space Flight
Center for NASA's Office of Space Science.

Credit: J. Trauger, JPL and NASA