Page 79 - Handbook of Gold Exploration and Evaluation

60 Handbook of gold exploration and evaluation

almost 10,000 times smaller than optical telescopes. To achieve an optical
resolution equal to that of a moderately sized optical telescope, a radio telescope
observing at 1 cm would have to be 2 km across. The solution to this handicap
was overcome by electronically combining radio signals from space using two
or more telescopes in unison. Since the two telescopes are at slightly different
distances from source there is a phase difference, which must be resolved.
Merging the two signals electronically so that they are detected simultaneously
by the same dish does this. Pairs of telescopes situated thousands of miles apart
provide resolutions as small as 0.001 arc seconds or even less, much smaller
than can be obtained using optical telescopes. The data from each telescope is
recorded on magnetic tapes and played back into a computer that combines the
signals as if they were from a single telescope.
However, although most visual and radio wavelengths penetrate the Earth's
atmosphere, radiation at the following wavelengths is observable only by
telescopes located in space. This is because:

· Most infra-red is absorbed by the atmosphere.
· Nearly all ultraviolet is absorbed.
· All gamma and X-ray radiation is absorbed.

In 1959 a space probe launched by the Soviet Union flew within 3,700 miles of
the moon. Scientific data gathered by Luna 1 sensors was relayed by radio
transmitters back to Earth. Since then several other space probes have orbited
the moon or landed on it. Space travel became a new technology and a complete
new phase of space exploration commenced. Gold-coated visors protected the
astronauts' eyes from searing sunlight on the Apollo moon landing in 1969 when
men landed on the Moon and returned safely to Earth. The charged-couple
device, which used gold to collect electrons generated by light, was invented in
1970. This invention has subsequently been used in hundreds of military and
civilian applications including video photography. Spacecraft missions provided
and are providing information both within the solar system and around stars in
outer space. Deployment of the Hubble Space Telescope provides a new means
of taking measurements of other galaxies in outer space

Space telescopes

The Hubble Space Telescope launched in 1990 was the state of the art model at
the end of the 20th century, working around the clock to investigate secrets of
the universe. Hubble orbits 600 km above Earth and is the first scientific mission
of any kind that is specifically designed for routine servicing by space-walking
astronauts. It has a visionary, modular design that allows the astronauts to take it
apart, replace worn out equipment and upgrade instruments. Periodic service
calls ensure cutting-edge technology and views of the Earth that cannot be made
using land-based telescopes or other satellites. Three such missions have been