Astronomers use radio telescopes to explore the Universe by detecting radio waves emitted by objects in space. Radio telescopes provide alternative views to optical telescopes, they can detect invisible gas, and can reveal areas of space that may be obscured with cosmic dust.
Radio telescopes can be used individually or they can be linked together to create a telescope array known as an interferometer. The SKA will be the world’s largest interferometer.
Radio wave receptors, or antennas, detect the relatively long wavelength (low frequency) radio waves that penetrate the Earth’s atmosphere. These radio signals have frequencies between about 30 MHz and 40 GHz, which is equivalent to, wavelengths from 10 m down to 7 mm. The SKA will observe at a frequency range from 70 MHz to 10 GHz which is equivalent to wavelengths of 4 m to 3 cm.
The hydrogen atom comprises a proton and an electron. While not strictly little spheres, both the electron and proton do have a property known as ‘spin’. The spins of the two particles can be aligned or anti-aligned. If spins of the electron and proton in a hydrogen atom are aligned, the atom has slightly more energy than if the spins are anti-aligned. A hydrogen atom can make a transition from the aligned state to the anti-aligned state. In doing so, it emits radio energy at a wavelength of 21 cm or a frequency of 1420 MHz. Conversely, in order for the atom to make the transition from anti-aligned to aligned, the atom has to be exposed to 21 cm wavelength radiation, from which it can absorb radio energy.
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