Fort Davis, Texas — McDonald Observatory staff
are cutting garage-door-sized holes all around
the enclosure of the 9.2-meter Hobby-Eberly Telescope
(HET), and fitting them with giant steel “venetian
blinds” called louvers. This should allow the HET,
one of the world’s largest telescopes, to operate at
the same temperature as the outside air.

“You can’t beat Mother Nature,” said HET Chief
Engineer John Booth. “This should go a long way
toward allowing the HET to produce sharp
astronomical images.

“The problem is heat. As the temperature drops
outside at night, the walls of the dome keep the
air inside warmer than the air outside,” Booth
said. “When the warm air and cool air mix, at
the location of the dome opening, they bend the
light rays coming into the telescope. This mixing
creates what we call bad “seeing” — it blurs the
images of stars and galaxies we want to study.”

So after consultations and tests, McDonald Observatory
decided to “open up the dome,” to allow wind to
blow through the building. This is being done by
cutting 15-foot by 17-foot windows in the bottom
half of the building, called the ring wall. The first
cut was made on January 8. After each opening
is cut, a pair of louvers — which looks like a huge
venetian blind with four blades — is lifted by a crane
attached to the rotating portion of the dome. Each
pair of louvers weighs 5,000 pounds — about the
same as a large sport utility vehicle. The first louver
was lifted into place on February 1. In all, 26 louvers
(12 pairs and two singles) will be installed at the HET
by May.

This is the first stage in the $500,000 HET dome
ventilation project. Smaller heat sources, including
a few instruments on the telescope itself, will also
be shielded or moved out of the dome. Later, smaller
louvers will be installed in the upper, geodesic part
of the dome.


NOTE TO EDITORS: Images of the louver installation,
and an artist’s conception of the HET enclosure after
the project’s completion, are available for download