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 on which our RadioJove telescope had worked until 2009 (and captured radio bursts from the Sun). The yellow line indicates the wavelength of 21cm, which is observed by the ESA-Haystack telescope. The red line marks 12 GHz, where the ESA-Dresden telescope works. The vertical axis is 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 correspond to the thermal noise produced in the receiver itself (at room temperature).

Here is a JAVA applet which is an "animation" of the above plot. Clicking on the plot, 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.

Introductory material on radio astronomy

There is a wealth of material on various aspects of radio astronomy 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 how we measure 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:

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last update: Apr. 2013 J.Köppen