In Hong Kong, it is becoming difficult to find a starry night. Radio astronomy may be helpful in overcoming this difficulty since radio telescopes are usable at all times and at any weather conditions. However, radio telescopes do have their own shortcoming. Firstly, radio astronomical images are not as fascinating as optical images. Moreover, they do not work like optical telescopes which can receive all visible wavelengths and then produce monochromatic signals by means of filters.

Radio waves emitted by neutral hydrogen in the Universe are detectable and the frequency is around 1.42 GHz. In Hong Kong, this frequency is protected by international treaties and reserved for radio astronomical observation. In December of 1933, Karl Jansky, a radio engineer published his discovery of "Electrical Disturbances Apparently of Extraterrestrial Origin? It was understood that sunspot activity was not at its peak in 1932 and hence the radio waves were unlikely to be emitted from the Sun. Karl deduced that these waves came from the Milky Way. Unfortunately, astronomers at that time paid only little attention to this phenomenon. Much worse, the United States was suffering from the Great Depression and nobody would support the research in this area. It was not until years later that the first all sky radio map was obtained by amateur astronomer Grote Reber, who had spent lots of effort in the measurement. He found that there was a fundamental difference 
between the optical and radio sky. He discovered that apart from the Sun, no visible celestial objects would emit radio waves. However, at certain locations in the Milky Way, strong radio waves were detected. In modern radio astronomy, these radio celestial bodies are called "Discrete sources? Cassiopeia A, Cygnus A and Taurus A are some examples of discrete sources. The letter "A" represents a strong radio source.

In China, the Chinese Academy of Sciences is supporting a new project called "Pre-research on Five hundred meter Aperture Spherical Telescope (FAST)*" The Project aims to build a fixed spherical reflective antenna of 500 metres aperture at a bowl-shaped valley of some 500 metres wide in a mountainous area in Guizhou and this reflective antenna will be named as "Soft antenna". The advantage of FAST lies in its sensitivity which is double that of the Arecibo Radio Telescope, the world's largest radio telescope, and one order of magnitude higher than fully steerable 100-meter diameter antennas.

On the other hand, the University of Hong Kong is planning to build a small radio telescope, with a 2.3-metre aperture and weighs 73 kg with automatic tracking, for teaching purpose. If everything goes well, it can scan a radio map of the Milky Way.

Hopefully, people in Hong Kong will have a chance to operate a radio telescope soon.

Reference :
*1. www.bao.ac.cn/bao/LT/
2. www.jb.man.ac.uk
3. www.nrao.edu