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First Giant Magellan Telescope Mirror Casting is 'Perfect'



 
 
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Old October 28th 05, 05:47 PM
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Default First Giant Magellan Telescope Mirror Casting is 'Perfect'

FIRST GIANT MAGELLAN TELESCOPE MIRROR CASTING IS 'PERFECT'
From Lori Stiles, UA University Communications, 520-621-1877

October 27, 2005

-----------------------------------------------------------------
Science contact information, downloadable images listed at end of
release

News media should coordinate access to the Mirror Lab casting area with
Elizabeth Alvarez of Steward Observatory, 520-626-9778
-------------------------------------------------------------------

The University of Arizona Steward Observatory Mirror Lab's casting of
the
first mirror for the Giant Magellan Telescope (GMT) "appears to be
essentially perfect," UA Steward Observatory Director Peter
Strittmatter
said after astronomers got their first look at the glass last Friday.

"We're very happy to see this one come out looking so gorgeous," Mirror
Lab
Technical Director J. Roger Angel said. "We'll see more once the mold
is
removed, but so far, looking through the front surface, it looks
great."

The mirror is the first of seven 8.4-meter (27-foot) mirrors that the
Mirror Lab is making for the Giant Magellan Telescope. The GMT is the
world's first extremely large ground-based telescope to start
construction.

The colossal telescope will feature six giant off-axis mirrors around a
seventh on-axis mirror. This arrangement will give it a 22-meter
(72-foot)
aperture, or 4.5 times the collecting area of any current optical
telescope.
It will have the resolving power of a 24.5-meter (80-foot) diameter
telescope, or 10 times the resolution of the Hubble Space Telescope.
The GMT
is slated for completion in 2016 at a site in northern Chile.

Randy Lutz and the Mirror Lab casting team knew they had a superb first
GMT
mirror blank when they removed the casting furnace lid Oct. 21. But
they
aren't standing around to admire their handiwork. They?re racing to
remove
furnace walls and ready the mirror blank for moving off the furnace
hearth.

"We're very eager to get on to the critical part of why we made this
mirror
-- to the polishing and the testing, which are really the new
ground-breaking steps in making this mirror because its shape is so
different," Angel said. "We're moving fast because we want to get on
with
casting the next mirror, a 3.7-meter mirror that will be needed to
measure
the shape of the GMT primary mirrors."

Mirror Lab workers are about to disassemble their facility's 7.5-story
test
tower (that's 27 meters, or 88 feet) and construct a higher tower that
will
hold the 3.7-meter (12-foot) mirror for measuring the off-axis GMT
mirrors.
The test mirror is crucial for making measurements needed for shaping
all
the primary mirrors so they gather and focus light as a single
gargantuan
primary mirror.

Meanwhile, Steward Observatory Mirror Lab scientists Buddy Martin and
Jim
Burge are already polishing a one-fifth scale prototype of the GMT
primary.
Polishing the full size off-axis mirror will be a huge step forward in
the
GMT project, Angel said.

For the casting last July, Mirror Lab workers used 40,000 pounds of
Ohara
E-6 borosilicate glass. The furnace hit peak temperature, 2,150 degrees
Fahrenheit (1,178 Celsius) on July 23. As the furnace rotated at 5
revolutions per minute, glass melted around the 1,681 hexagonal cores
in the
mold. This created a 'honeycomb' mirror blank with a faceplate of the
desired curvature. The honeycomb mirror weighs only a fifth as much as
would
a solid mirror of the same size.

The first GMT primary is the third 8.4-meter mirror cast at the Steward
Observatory Mirror Lab. The GMT builds on the very successful 6.5-meter
(21-foot) Magellan telescopes which many of the same GMT partners
operate in
Chile.

Eight institutions are partners in the GMT. They are the Carnegie
Observatories, Harvard University, Smithsonian Astrophysical
Observatory,
University of Arizona, University of Michigan, Massachusetts Institute
of
Technology, University of Texas at Austin, and Texas A & M University.

The two other 8.4-meter mirrors cast at the Mirror Lab are at the Large
Binocular Telescope (LBT) on Mount Graham, Ariz. U.S., Italian and
German
partners in the LBT released 'first light' images obtained with the
first of
the LBT's primary mirrors yesterday (Oct. 26). The LBT, the forerunner
of
the GMT, will be the world's most powerful single telescope when its
two
primary mirrors, mounted side-by-side, become operational in 2006.
------------------------------------------------------
Contact Information
Peter Strittmatter Director, Steward Observatory
520-621-6524

J. Roger Angel. Technical Director, SO Mirror Lab
520-621-6541,


Related Web sites
Giant Magellan Telescope -
http://www.gmto.org/
Steward Observatory Mirror Lab - http://mirrorlab.as.arizona.edu/

A high-resolution artist's illustration of the Giant Magellan Telescope
can
be downloaded at http://uanews.org/silk/request/gmt_4.jpg
ILLUSTRATION CREDIT: Todd Mason / Carnegie Observatories

Three high-resolution images of the solid GMT mirror found at -
http://uanews.org/silk/request/gmt1437.jpg
http://uanews.org/silk/request/gmt1441.jpg
http://uanews.org/silk/request/gmt1443.jpg

PHOTO CAPTION (gmt1437.jpg) - Mirror Lab casting team supervisor Randy
Lutz
(standing) and Damon Jackson check the first GMT mirror's surface after
the
furnace lid was removed, Oct. 21, 2005. (Photo: Lori Stiles, UA)

PHOTO CAPTION (gmt1441.jpg) - Mirror Lab casting team supervisor Randy
Lutz
(top) and Damon Jackson check the first GMT mirror's surface after the
furnace lid was removed, Oct. 21, 2005. (Photo: Lori Stiles UA)

PHOTO CAPTION (gmt1443.jpg) - Mirror Lab casting team member Damon
Jackson
checks the GMT mirror with an ultrasonic thickness gauge that measures
the
thickness of the faceplate with extreme accuracy, Oct. 21, 2005 (Photo:
Lori
Stiles, UA)

 




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