The longer wavelengths means that the radio waves have lower energy than optical light waves. In order to collect enough radio photons to detect a signal, the radio dishes must be very large. Both optical and radio telescope reflectors use a parabolic shape to perfectly focus the light to a point. Increasing the size of the radio dish is also necessary in order to improve the clarity of the radio images. I will discuss the issue of image clarity further in the next two sections.
Radio telescopes detect the emission from cool clouds of hydrogen in the space between the stars.
Hydrogen atoms are the most common type of atoms in the universe and much of the hydrogen gas is too far away from any star to produce emission in the optical wavelength band. Therefore, radio telescopes are a vital tool in understanding the universe. I will discuss further the use of radio waves to explore the material between the stars and the structure of our galaxy in the interstellar medium chapter .