Signal detection

1. Signal collection Light can be focused using a curved mirror like a lens. Wire mesh can be used to reflect radio waves. This is possible if the wavelength of the radio waves we want to detect is at least ten times the size of the mesh spacing. Building a telescope with a mesh reflecting surface is much cheaper. The dishes will also weigh less. Radio Telescopes Signal detection Radio waves can also be focused using a curved surface. The reflecting surface A radio receiver converts radio waves into electronic signals. Radio waves from astronomical sources are very weak telescope receivers and so must be highly sensitive. has to be much larger though, since radio wavelengths are about 100,000 times longer than visible light. After focusing, the radio waves are reflected back to a receiver. Image Courtesy of M. Crofts Objects at higher temperatures than 0K emit E-M radiation. Receivers in radio telescopes have to be cooled to almost absolute zero to avoid the equipment in them emitting too much radiation and drowning out the Image Courtesy of M. Crofts very faint signals from astronomical sources. Image courtesy of NRAO/AUI A contour map draws lines between points of equal intensity, just like the isobars on a weather map. Large counterweights balance the telescope on its mount. Radio telescopes don’t take colour pictures (remember colours are different wavelengths). Instead, the data from the telescope has to be made into an image with a computer. As the Earth rotates the sky appears to move. Telescopes use carefully controlled motors to follow the motion of objects in the sky. False colour images use different colours to represent different levels of intensity. The galaxy to the right is NGC1275. At its centre is a bright radio source, Image courtesy of NRAO/AUI Image HST THE IMAGE TRACKING