Astronomy in the deep freeze
Glossary
brown dwarf. An object in space, intermediate in mass between a small star and a large planet. Brown dwarfs are very difficult to detect because they are very faint; as they age and cool they become even fainter. The radiation they emit is primarily in the near infrared. For more information see Brown dwarfs (Chandra X-ray Laboratory, USA).
electromagnetic radiation. Electromagnetic radiation is simply energy which travels through space at about 300,000 kilometres per second – the speed of light. We imagine radiation moving like a wave. The distance between two adjacent wave crests is called a wavelength. The shorter the wavelength, the more energetic the radiation is said to be. Also, the shorter the wavelength, the greater the frequency of the radiation. Other than wavelength, frequency and energy there is no difference between a radio wave, an X-ray and the colour green. They all possess the same physical nature. For more information see Back to Basics: Electromagnetic radiation (Australian Academy of Science) and Electromagnetic Spectrum (NASA Goddard Space Flight Center, USA).
electromagnetic spectrum. The complete range of frequencies (or wavelengths) of electromagnetic radiation. For more information on electromagnetic radiation and the electromagnetic spectrum see Measuring the electromagnetic spectrum (High-Energy Astrophysics Learning Center, Goddard Space Flight Center, USA) and More about the electromagnetic spectrum (High-Energy Astrophysics Learning Center, Goddard Space Flight Center, USA).
galaxy. Huge regions of space that contain hundreds of billions of stars, together with planets, glowing nebulae, gas and dust.
infrared. The part of the electromagnetic spectrum between visible light and microwaves. The wavelength of infrared light is between 0. 7 micrometres (0.0007 millimetres) and 1 millimetre. These wavelengths are longer than those of visible light, but shorter than those of microwaves. (The prefix 'infra' means 'below; infrared refers to radiation below the frequency of red light.)
infrared telescope. A telescope designed to observe in the infrared section of the electromagnetic spectrum. Infrared telescopes look like optical reflecting telescopes and operate in a similar way. The infrared radiation is collected and focused by mirrors onto detectors sensitive to infrared.
One problem with infrared telescopes is that the telescope itself is a source of unwanted infrared radiation, but this is minimised by cooling the components of the telescope with liquid nitrogen for near infrared observations and with liquid helium for the far infrared.
near, mid and far infrared. Infrared radiation is often subdivided into three regions – near, mid and far. Near infrared includes shorter wavelengths of infrared radiation, closer to visible light; far infrared includes longer wavelengths of infrared radiation, closer to microwave radiation. For more information see Near, mid and far infrared (Infrared Processing and Analysis Center, USA)
optical telescope and radio telescope. Telescopes are instruments that are used to observe radiation from a distant object. They can produce an image of the object or enable the radiation to be analysed.
Optical telescopes are used to observe wavelengths of visible light. They make distant objects distinct and visible by producing a magnified image of the object and by collecting more light than the naked eye. There are two main types of optical telescopes: refracting telescopes use lenses and reflecting telescopes use mirrors.
Radio telescopes are used to observe longer wavelengths of radiation (radio waves), with large dishes to collect and concentrate the radiation onto antennae for detection.
For more information see It takes more than one kind of telescope to see the light (Science@NASA, USA).
red dwarf. A small, very faint and cool dwarf star. It is thought that red dwarfs are the most common star in the universe. For more information see A galaxy dweller's guide to planets, stars and dwarfs (Space Telescope Science Institute, USA)
Page updated August 2006.