Page 3 - 83 basic knowledge of astronomy

1 ‘Windows’ for Ground–based Astronomy

Figure 1 shows how the Earth’s atmosphere transmits electromagnetic waves
from the Universe. The curve over the hatched area in this figure corresponds
to the height in the atmosphere at which the radiation is attenuated by a
factor of 1/2.

Figure 1: ‘Windows’ for ground-based astronomy (from Rohlfs & Wilson,
2001).

This figure shows that the Earth’s atmosphere is largely transparent in
the radio (15 MHz – 300 GHz) and visible light (360 THz – 830 THz) regions
of the electromagnetic spectrum. These two regions are the main ‘windows’
for ground-based astronomical observations. VLBI (Very Long Baseline In-
terferometry) is one of the techniques used to observe astronomical radio
sources through the ‘radio window’.

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