Radio waves can be anywhere from a fraction of one millimeter long to 300 meters long. Many objects in the universe emit photons across the entire electromagnetic spectrum, although we can only see those that fall in the visible portion of the spectrum. Optical Versus Radio Astronomy Optical Observatory Optical Telescope Optical Astronomy Photo Astronomy is divided into several branches, each involving a different portion of the electromagnetic spectrum. Optical astronomy , which is the most widely-known and popular branch of astronomy, is the study of the universe in the visible light region of the electromagnetic spectrum. When we think of optical astronomy, we think of looking through a telescope.
Optical telescopes have mirrors or lenses which collect or refract light.
Steerable Dish Radio Telescope Fixed Kraus-Type Radio Telescope Radio astronomy is the study of the universe in the radio portion of the electromagnetic spectrum, which is from a fraction of one millimeter to 300 meter wavelengths. To study the universe at radio wavelengths, radio astronomers use radio telescopes, which are entirely different from optical telescopes. Although radio waves can't be seen, they can be heard as a hiss not unlike the static between stations on the radio. Radio astronomers have made some exciting discoveries. The Big Ear radio telescope was used in the 1960s to form a giant picture of what the sky looks like in the radio region of the electromagnetic spectrum.