A visit to Mansfield and Sutton Astronomical Society gave me opportunity to test out the portable radio telescope, pictured below.
As you can see the arial is of a dish design mounted on a sturdy tripod. An equatorial mount allows the telescope to follow the arc of the target as the earth rotates. There is a receiver and recorder, with the whole telescope being powered by a battery pack.
The secret weapon amongst all this is a tiny silver sequin. For those of you with good eyesight, it is in the centre of the dish and reflects light onto the receiver. This allows the user to see when the dish is correctly aligned with the sun.
Since the earth rotates, astral bodies appear to move through the sky. For example the Sun rises in the East and sets in the West. This is actually the Earth rotating through the day so that the Sun appears to be in a different position.
If we use a fixed mount to align our telescope, we can therefore expect the Earth’s rotation to move the telescope, hence moving away from its initial position and losing its target.
We can get round this by using an equatorial mount. This mount allows the telescope to rotate with the rotation of the Earth, which can be done manually, or automatically with the addition of a motorised clock drive. The below picture is of a Celestron equatorial mount. The one shown comes with a Goto finder where you type in the name of the target and the finder goes straight to it.
If we have got our telescope working correctly, we should manage to find radio waves. We targeted the Sun. I should mention at this point that you don’t need a clear sky to use a radio telescope as radio waves will pass through the Earths atmosphere. This is an obvious advantage over optical telescopes, which require clear night time skies. The downside of cloud, is actually locating the Sun. Our radio telescope works within a 3 degree arc, just outside of that angle and there will be no signal. One of our more resourceful members uses a mobile phone tracker attached to the telescope to locate the sun.
Fortunately for us we had clear skies so knew exactly where the Sun was. The telescope was pointed towards the Sun, avoiding direct eye contact, but looking for the reflection from our high tech sequin. I wonder if NASA use sequins?
As the reflection passed over the receiver there was a clear audible signal from our recorder, and the needle on the gauge swung accordingly. When the reflection moved off the receiver, the signal was lost. Success, we had managed to detect radio waves emitted from the Sun.
Building a picture
Ours is obviously very basic equipment, but is easy to build, setup, and use. More accurate, and expensive, equipment can focus in much more accurately than our 3 degree arc. With more advanced radio telescopes we can focus in on a small part of the surface of the Sun. As we move our advanced telescope along the Sun’s surface we can record the differences in signal strength, which is then translated to form a picture of the surface as a whole.
Pictures of the Sun obtained via radio telescope are actually just spikes and troughs in the signal, to which we add artificial colours according to the signal strength, and form a picture.
If you fancy seeing our radio telescope, or other monitoring equipment, in action, there are events organised throughout the year. Have a look at our events calendar.