and Cosmology

1.3 The Tools of Extragalactic Astronomy
Fig. 1.22. The 30-m telescope on Pico
Veleta was designed for observations in
the millimeter range of the spectrum. This
telescope, like all millimeter telescopes,
is located on a mountain to minimize the
column density of water in the atmosphere
23
Fig. 1.23. The JCMT has a 15-m dish. It
is protected by the largest single piece of
Gore-Tex, which has a transmissivity of
97% at submillimeter wavelengths
1 μm λ 2.4 μm) which render ground-based observations
possible. In the mid-infrared (MIR, 2.4 μm
λ 20 μm) and far-infrared (FIR, 20 μm λ
300 μm) regimes, observations need to be carried out
from outside the atmosphere, i.e., using balloons, highflying
airplanes, or satellites. The instruments have to
be cooled to very low temperatures, otherwise their own
thermal radiation would outshine any signal.
The first noteworthy observations in the far-infrared
were made by the Kuiper Airborne Observatory (KAO),
an airplane equipped with a 91-cm mirror which operated
at altitudes up to 15 km. However, the breakthrough
for IR astronomy had to wait until the launch of IRAS,
the InfraRed Astronomical Satellite (Fig. 1.24). In 1983,
with its 60-cm telescope, IRAS compiled the first IR
map of the sky at 12, 25, 60, and 100 μm, at an angular