Sky
& Telescope
 | | The
cloud-covered surface of Venus was revealed by radar observations taken by the
recently completed 100-meter Robert C. Byrd Green Bank Telescope in West Virginia
and the newly upgraded 305-m Arecibo telescope in Puerto Rico. This view shows
details as small as 5 kilometers across. Courtesy of Donald Campbell and others,
National Radio Astronomy Observatory, National Astronomy and Ionosphere Center.
Click on image for larger view. |
Yesterday,
astronomers released the first scientific images from the world's largest fully
steerable dish antenna. The team led by Donald Campbell (Cornell University) used
the 100-meter Robert C. Byrd Green Bank Telescope (GBT) in West Virginia to make
radar observations of Venus and a 150-meter-wide near-Earth asteroid in March.
The studies began by transmitting radio pulses toward the two objects using the
305-meter reflector in Arecibo, Puerto Rico. Both telescopes then listened for
the returning echoes after the pulses bounced off Venus and asteroid 2001 EC16.
The received signals from both telescopes were then combined to produce images
with greater detail than could be produced by the individual instruments.
The
images resolved details as small as 1 kilometer across on Venus's surface. This
capability may allow astronomers to detect future changes on the surface due to
volcanism, should the planet still be active. The radar data revealed that minor
planet 2001 EC16 is irregularly shaped and rotates once every 200 hours Ñ a very
slow pace for an asteroid. The views of 2001 EC16 demonstrate the power the Arecibo-GBT
combination will have in studying other near-Earth objects.
With an unobstructed
aperture 100 by 110 meters, the $75 million GBT stands 148 meters (485 feet) tall
and boasts almost two acres of reflecting surface made up of 2,004 aluminum panels.
Despite its size, the telescope will maintain a surface accuracy of 0.25 millimeter
thanks to a feedback system that adjusts the panels to compensate for minute structural
flexing of the dish. Such an accurate surface will allow observations at up to
80 gigahertz and a pointing accuracy of 1 arcsecond. The GBT is a vastly improved
replacement for the old 91-meter Green Bank Telescope that collapsed in November
1988. |
