observatory rotate either more rapidly or less rapidly toward a new target. Receiver The part of the radio telescope that detects long wavelength electromagnetic radiation and converts it to an electrical signal so that we can sense it. Recessional velocity The velocity at which an object moves away from an observer. The recessional velocity of a distant galaxy is proportional to its distance from Earth. Therefore, the greater the recessional velocity, the more distant the object. Red giant star An old, bright star, much larger and cooler than the Sun. Betelgeuse (alpha Orionis) is an example of a red giant. Redshift The lengthening of a light wave from an object that is moving away from an observer. For example, when a galaxy is traveling away from Earth, its light shifts to the red end of the electromagnetic spectrum. Reflection Reflection occurs when light changes direction as a result of "bouncing off" a surface like a mirror. Reflection occurs when light changes direction as a result of "bouncing off" a surface like a mirror. Half size glossary reflection 2x Reflector (reflecting telescope) A type of telescope, also known as a reflecting telescope, that uses one or more polished, curved mirrors to gather light and reflect it to a focal point. Refraction Refraction is the bending of light as it passes from one substance to another. Here, the light ray passes from air to glass and back to air. The bending is caused by the differences in density between the two substances. A type of telescope that uses a transparent convex lens to gather light and bend it to a focal point. Regolith The layer of loose rock resting on bedrock (sometimes called mantle rock), found on the Earth, the Moon, or a planet. Regolith is made up of soils, sediments, weathered rock, and hard, near-surface crusts. On the surface of the Moon, regolith is a fine rocky layer of fragmentary debris (or dust) produced mainly by meteoroid collisions. Relativity A theory of physics that describes the dynamical behavior of matter and energy. The consequences of relativity can be quite strange at very high velocities and very high densities. A direct result of the theory of relativity is the equation E=mc2, which expresses a relationship between mass (m), energy (E), and the speed of light(c). Resolution (resolving power) A measure of the smallest separation at which a telescope can observe two neighboring objects as two separate objects. Resolve The ability of a telescope to distinguish objects that are very close to each other as two separate objects. Revolution The orbital motion of one object around another. The Earth revolves around the Sun in one year. The moon revolves around the Earth in approximately 28 days. Right ascension (RA) A coordinate used by astronomers to locate stars and other celestial objects in the sky. Right ascension is comparable to longitude, but it is measured in hours, minutes, and seconds because the entire sky appears to pass overhead over a period of 24 hours. The zero hour corresponds to the apparent location of the Sun with respect to the stars on the day of the vernal (spring) equinox (approximately March 21).
You've reached the end of your free preview.
Want to read all 29 pages?
- Spring '14
- Hubble Space Telescope