Radioastronomy is a branch of astronomy which looks at the radiowaves emitted from various astronomical objects. Stars, galaxies, pulsars and masers all emit types of radio waves. The discovery of CMBR (Cosmic Microwave Background Radiation) was a major step forward in this branch of science, as it acts as a systematic error against data collected by the surveying equipment, and this allowed the science to progress. Radio Astronomy is done with either a single telescope or using radio interferometry in which multiple telescopes are linked together and combine to one very sensitive device.
Radio telescopes are very big, there surface area’s have to be big as the wavelegnth of a radio wave can be anything from the order of metres to kilometers, and have a low signal to noise ratio. Interferometers overcame this difficulty of high resolution images from a singular telescope, invented by British astronomer Martin Ryle. An Interferometer consists of many telescope some ditance apart from each other observing the same object from multiple observation points, they are then all linked together and a process called Aperture Synthesis is used to vastly increase the resolution.
To produce a high quality image the distance between telescopes must be varied and the more telescope the more differentiation in distances we get. The seperation between any two of these telescopes when observed from the emitter is called a baseline. An interferometer will consist of as many telescopes as possinble in order to get the best quality image by superposing the images ( the VLA – Very Large Array; has 27 telescopes which give 351 different baselines between them and therefore a high quality image)
The distances shown on images taken by a standard VLA image shows a range of around 4000 light years on one image, this is a very big distance and as such there was room for improvement in the technology, in the 1970’s improvements in communications methods meant that telecopes all over the surface of the earth could connect together into one huge network. The VLBA ( Very Long Baseline Array) can record images 0.1 of a light year across, this is an improvement of 40,000 times. This effect give a similar result as having one giant dish hundreds of kilometers wide.
Radio Astronomy shows us the reminents and activity of things like supernovae, as well as the sun, the galactic centre of the Milky Way (Sagittarius A), active galactic nuclei, galaxy clusters, cosmic backgorund radiation and black body emitters. Astronomers use Interferometers to measure the diameter of some stars, Betelguese was the first to have its diameter measured in 1920 – 1921 by the Michelson stellar interferometer.
