Brings Astronomers Closer to Unveiling the Entire Sky with Adaptive Optics

MAUNA KEA, Hawaii (Jan. 4, 2002 ) – The W. M. Keck Observatory, home to the
world’s two largest telescopes, and the Lawrence Livermore National
Laboratory (LLNL) have created a “virtual” guide star that will greatly
increase the ability of the Keck II telescope using adaptive optics to
resolve fine details of astronomical objects. Installed in 1999, the Keck
adaptive optics system has enabled astronomers to minimize the blurring
effects of the Earth’s atmosphere, producing images with unsurpassed detail
and resolution. The adaptive optics system uses light from a relatively
bright star to measure the atmospheric distortions and to correct for them,
but only about one percent of the sky contains stars sufficiently bright to
be of use. The new virtual guide star will enable Keck astronomers to study
nearly the entire sky with the high resolution of adaptive optics.

The virtual guide star, which achieved “first light” on December 23, was
created using a 20-watt dye laser to illuminate a diffuse layer of sodium
atoms that exists 60 miles (95 km) above the Earth’s surface. When
activated by the laser, the sodium atoms produced a very small source of
light, less than 3 feet (1 meter) in diameter, which allowed the adaptive
optics system to measure the distortions of the atmosphere. The resulting
virtual star was measured at 9.5 magnitude, about 25 times fainter than
anything that can be seen by the unaided eye, but bright enough to operate
the adaptive optics system. The star appeared orange, the familiar color of
common low-pressure sodium vapor street lights. The laser guide star system
was funded by the W. M. Keck Foundation, with additional funding provided by
the National Aeronautics and Space Administration (NASA) and the National
Science Foundation’s Center for Adaptive Optics (CfAO). It was developed in
collaboration with the Lawrence Livermore National Laboratory (LLNL).

Adaptive optics refers to the ability to compensate or adapt to turbulence
in the Earth’s atmosphere, removing the blurring of starlight. Adaptive
optics systems measure the distortions of the light from a star and then
remove the distortions by bouncing the light off a deformable mirror that
corrects the image several hundred times per second. With the Keck adaptive
optics system, astronomers are obtaining infrared images with four times
better resolution than those produced by the Hubble Space Telescope, which
orbits high above the Earth’s atmosphere. Many significant discoveries have
already been attributed to Keck adaptive optics, and the Keck laser guide
star system will lead to many more.

“We asked for an early present this year, and just before Christmas we were
given a virtual star that will dramatically increase the research
capabilities of the world’s largest telescope,” said Dr. Frederic Chaffee,
director of the W. M. Keck Observatory. “This effort could not have been
possible without the talent and dedication of our adaptive optics and laser
guide star teams. We couldn’t be happier with these results, and we look
forward to fully integrating the laser with our adaptive optics system by
the middle of 2002.”

The Keck virtual guide star system consists of a dye laser that is used to
produce light with the wavelength of the atomic sodium resonance line at 589
nm. The 20-watt output of the dye laser is projected out of a 20-inch (50
cm) lens attached to the side of the 10-meter Keck II telescope.

“We have seen lasers develop into powerful tools in fields ranging from
medicine, to laser printers to compact disc players. Our new virtual guide
star marks the start of a new era, when we’ll see lasers contributing to
astronomy as well,” said Claire Max of LLNL, principal investigator for the
Keck laser project.

The main components of the Keck adaptive optics system are a wavefront
sensor camera, a fast control computer and a deformable mirror. The
wavefront sensor camera measures distortions due to atmospheric turbulence
using light from the guide star. A control computer computes the wavefront
distortion up to 670 times a second and sends commands to the deformable
mirror. The deformable mirror, about six inches (15 cm) in diameter, is
made out of a thin sheet of reflective glass controlled by 349 actuators
that can adjust the shape of the mirror by several microns, a distance large
enough to correct for atmospheric distortions.

Center for Adaptive Optics

Support for the Keck virtual guide star adaptive optics program is provided
in part by scientists at the Center for Adaptive Optics (CfAO), a national
center devoted to the advancement and application of astronomical adaptive
optics technology. Additional information is located at the CfAO Web site

Lawrence Livermore National Laboratory

The Keck virtual guide star system is the world’s most powerful laser
currently in use at an astronomical telescope. The laser was developed by
the Lawrence Livermore National Laboratory (LLNL) and LLNL staff played a
key role in the deployment of the laser at the telescope. LLNL is a
national security laboratory with a mission to ensure national security and
apply science and technology to the important issues of our time; advanced
lasers represent one of the Laboratory’s core technology areas. LLNL is
managed by the University of California for the U.S. Department of Energy’s
National Nuclear Security Administration. For more information visit the
LLNL Web site at

The W. M. Keck Foundation

The W. M. Keck Foundation provided the bulk of the capital to build the two
10-meter telescopes as well as the adaptive optics and laser guide star
systems. The W. M. Keck Foundation is one of the nation’s largest
philanthropic organizations, focused primarily on the areas of medical
research, science, and engineering. The Foundation also maintains a program
for liberal arts colleges and a Southern California Grant Program that
provides support in the areas of civic and community services, health care
and hospitals, precollegiate education, and the arts. For more information,
visit the Foundation’s Web site at

W. M. Keck Observatory

The W. M. Keck Observatory, operated by the California Association for
Research in Astronomy (CARA), provides astronomers from associated
institutions access to two 10-meter telescopes, the world’s largest. Each
telescope features a revolutionary primary mirror composed of 36 hexagonal
segments that work in concert as a single piece of reflective glass to
provide unprecedented power and precision. Each telescope stands eight
stories tall and weighs 300 tons, yet operates with nanometer precision.
The observatory is operated by the California Institute of Technology, the
University of California, and the National Aeronautics and Space
Administration (NASA), which joined the partnership in October, 1996. For
more information, visit the W. M. Keck Observatory Web site at or send e-mail to:

Images available at: