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1. Introduction

People have looked at the night sky since the very beginning of human existence on this earth. Their view has, however, been limited to the very narrow range of wavelengths that the eyes are capable of detecting. Imagine what the night sky would look like if our eyes were sensitive to other parts of the electromagnetic spectrum.

There are certain wavelengths that would not be visible from the earth's surface because of the atmosphere. If we look for the part of the spectrum that is most accessible from the ground we would arrive at the radio regime. This spans wavelengths ranging from less than a millimeter to several meters as compared to the optical wavelengths which range from 400 to 700 nanometers. Our view of the universe with eyes sensitive to the radio regime would look very different from our current view.

Since our eyes are limited to the optical regime we have to use other means of detecting the rich store of information that is available in a radio view of the skies. This branch of astronomy is known as radio astronomy.

The goals of radio astronomical observations are similar to those at optical or any other wavelength astronomy - to study the characteristics of an object emitting these waves. The methods used in radio astronomy are the same as those used in any branch of science - testing a hypothesis with experiments and observations.

Many objects in the universe emit radio waves. The "view" of an object as seen in the radio wave region can be quite different from what is seen in the visible light region. This points to different mechanisms causing the radio emission as compared to the optical emission. Comparative studies of objects in the emission from different wavelengths can teach us a lot about the processes that go on in the universe.

As an example, here are three images of the sun made at three different wavelengths:

Sun picture #1
Sun picture #2
Sun picture #3
H-alpha image (optical wavelengths - 6563 Angstroms) on 3/30/98
H-alpha image (optical wavelengths - 6563 Angstroms) on 3/30/98
Soft X-ray image on 3/30/98

Daily images of the sun at various wavelengths such as the ones above can be obtained from a NASA web site.

It is immediately obvious that the above images show the sun as being very different at the three wavelengths. By combining the information obtained from the three images astronomers can study many aspects of the sun, the sunspots, the solar flares and prominences and all the other kinds of activities on the surface of the sun.

The aim of this tutorial is to provide an introduction to the basics of radio astronomy and introduce you to the techniques that allow radio astronomers to obtain and analyze data from radio telescopes.

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