Fundamentals of Radio Astronomy


Joachim Köppen Strasbourg 2010


This is the radio spectrum of astronomical sources (from the book "Radioastronomy" by John Kraus, W8JK). The green line marks 20 MHz, the frequency of the RadioJove receiver (to capture radio bursts from Jupiter and the Sun; ours was operational between 2003 and 2009, and had to be closed down because the evergrowing electronic pollution had rendered observations useless). The red line marks 12 GHz, where the ESA-Dresden telescope works. The blue line is the frequency of the 21 cm line of atomic hydrogen - at a frequency of 1420.406 MHz - where the ESA-Haystack telescope observes. The vertical axis shows the flux of the sources, that is the power per unit surface area of the telescope. The horizontal lines marked with 1m, 10m, and 100m indicate the sensitivity that can be achieved by radio telescopes of that diameter: they show the fluxes which just equal to the thermal noise produced in the receiver itself (at room temperature).


Introductory material on radio astronomy

There is a wealth of material on various aspects of radio astronomy which is available on the Internet, either by professional institutions or by dedicated amateurs. It is well worth "googling" for a while on the Net to find information suited to one's particular taste and level. Here are a few references that we found quite useful:


Some essential definitions and relations

For the interpretation of observations it is necessary to clarify what is it that we measure of the radiation. In particular, we have to distinguish between two quantities, the flux and the intensity. In radio astronomy, we speak of antenna temperature and brightness temperatures:


Here is a preliminary version of a JAVA applet which is an "animation" of the plot shown at the top. You can read off the fluxes, apparent brightness temperatures (if one assumed a unity solid angle for the source!!), antenna temperatures and signal-to-noise ratios for a given antenna size ... (this has to undergo further improvements)


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last update: Feb. 2010 J.Köppen