|BAS - Radio Astronomy|
Notes and resources on Amateur Level Radio Astronomy
InformationThe electromagnetic spectrum covers a range from almost 0Hz up to 2.4×10E23 Hz (Gamma rays). Visible light makes up a small fraction of the total spectrum. Obviously visible light is covered by normal optical telescopes. As we already know radio telescopes exist to cover the 'non-visible' radio portion of the spectrum.
For the 'radio' portion of the spectrum this can be further divided into ranges as illustrated below, as allocated by international standards.
However for radio astronomy the radio waves obviously have to penetrate the Earths atmosphere, just like visible light for conventional telescopes. But the Earth's atmosphere is not transparent to all radio frequencies. It is opaque to a large proportion. In fact it is only transparent to a range of wavelengths from approximately 1cm to 1m, the rest is all absorbed by the upper atmosphere.
At the lower end of the radio spectrum frequencies are generated by natural phenominen like lightning and obviously by deliberate radio transmissions. Of course the same range of frequencies that cannot penetrate the atmosphere from space cannot radiate out. At low frequencies they are actually reflected too different extents by the Ionosphere as illustrated below.
These effects on the ionosphere can increase or decrease the distance to which these lower reflected frequencies are transmitted, so measuring the strength of radio signals over time can give an indication of changes in the upper atmosphere. Beacons, such as time signals, that transmit constantly at a fixed given power are usefull in this respect. Small receivers operating at very low frequencies can easily be built for this purpose.
Below is a table of frequencies that can penetrate the atmosphere and tend to be reserved for radio telescope use, that is not to say there would be no interference from other sources. There are other frequencies at the higher end not in this table, these are the frequencies that could be practical to work with for amateur radio astronomers.
British Astronomical Association Radio Astronomy Group on YouTube
Remote Radio Telescopes - SALSA
SALSA means "Such a lovely small antenna". This site provides access to three remotely controlled radio telescopes after you create an account. Works mainly in the Hydrogen Line region of the electromagnetic spectrum.