Glossary
Astronomy glossary
514 definitions · page 8 of 9.
- solar mass
- the amount of mass contained in the sun, about 330,000 times that of Earth’s mass
- solar system
- the system containing the sun and all the smaller bodies in orbit around it
- solar wind
- the stream of charged subatomic particles emanating from the sun
- solstice
- either of the two points on the celestial sphere where the sun is farthest north or south of the celestial equator; when the sun is at a solstice, the amount of daylight hours is greatest for summer and least for winter
- South Celestial Pole
- the point in the sky to which Earth's Geographical South Pole points
- space weathering
- the process of altering the surface of an object in space by such phenomena as micrometeoroid impacts, cosmic rays, and the solar wind
- space-time
- the intertwining of the three dimensions of space with one dimension of time within which events can be specified exactly
- special relativity
- the theory of relativity governing uniform motion; it states the equivalence of mass and energy and differs from Newtonian physics only when speeds approach that of light
- spectra
- plural of "spectrum" (the energy emitted by a radiant source)
- spectral class
- the designation of a star based on its spectrum, which is determined by its surface temperature
- spectral line
- a particular wavelength of light corresponding to the energy transition of a specific atom or molecule
- spectral type
- the designation of a star based on its spectrum, which is determined by its surface temperature
- spectrograph
- an instrument attached to a telescope to record the spectrum of an astronomical object
- spectroheliograph
- a device for photographing the sun in a single wavelength of light
- spectrometer
- an instrument attached to a telescope to record the spectrum of an astronomical object
- spectroscope
- an instrument for examining spectra
- spectroscopy
- the study of spectra from astronomical objects
- spectrum
- 1. the energy emitted by a radiant source 2. the entire range of electromagnetic radiation (light)
- speed of light
- the fastest possible speed in a vacuum, equivalent to 186,000 miles per second (300,000 km per second)
- spiral arm
- a concentration of gas, dust, and young stars that winds its way out from the nuclear region of a spiral galaxy
- spiral galaxy
- a spiral-shaped system of billions of stars, gas clouds, and dust
- standard candle
- an astronomical object of known luminosity; can be used to determine distances
- star
- a self-luminous sphere of hot gas held together by gravity; ordinary stars generate energy by nuclear fusion in their cores
- star atlas
- an collection of maps that marks the positions of stars, nebulae, galaxies, and other astronomical objects on a coordinate system
- star hopping
- the technique of using recognizable patterns of stars to “hop†from one part of the sky to another; useful in observing both with the naked eye and a telescope
- star party
- a gathering of people to observe the night sky
- starburst galaxy
- a galaxy undergoing an extremely high rate of star formation
- stellar evolution
- the life cycle of stars
- stellar wind
- a stream of electrically charged subatomic particles given off by stars
- stereocomparator
- An instrument that allows astronomers to view two images of the same region of sky simultaneously. Objects that have changed their brightness or position appear to stand out of the plane of the picture.
- sublimate
- the transition of a solid substance evaporating into a gas without passing through a liquid phase
- sublimated
- the transition of a solid substance evaporating into a gas without passing through a liquid phase
- sublimation
- the process by which a solid substance evaporates into a gas without passing through a liquid phase
- summer
- a season that begins around June 21 in the Northern Hemisphere
- sunspot
- a dark, temporary, relatively cool spot on the surface of the sun
- sunspot cycle
- a cycle averaging 11 years in which the number of sunspots increases and decreases
- supercluster
- an enormous congregation of galaxy clusters that stretches across hundreds of millions of light-years
- superfluid
- an unusual state of matter characterized by apparently frictionless flow, found only in liquid helium cooled to near absolute zero
- superior conjunction
- the configuration of an inferior planet when it lies on the far side of the sun
- superior planet
- a planet farther from the sun than Earth; includes Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto
- superluminal motion
- motion that appears to be faster than the speed of light
- supermassive black hole
- a black hole at the core of a galaxy that contains millions or billions of solar masses
- supernova
- the cataclysmic explosion of a star
- supernova remnant
- an expanding cloud of gas that represents the outer layers of an exploded star
- synchronous rotation
- when a satellite rotates at the same rate at which it revolves around a more massive object; a body with synchronous rotation shows only one hemisphere to the object it orbits
- synchrotron emission
- electromagnetic radiation from high-energy electrons moving in a magnetic field
- tera
- a trillion (1,000,000,000,000 in American usage)
- terminator
- the boundary on a planet or moon separating the illuminated side from the unilluminated.
- terrestrial
- of or relating to Earth
- terrestrial planet
- a small, rocky planet such as Mercury, Venus, Earth, and Mars
- thermal radiation
- electromagnetic radiation emanating from any object not at absolute zero
- tidal force
- the difference in gravitational force between two points on an object caused by the gravity of another object; the tidal force often leads to a deformation of an object
- tides
- the distortion of a body caused by the gravitational influence of another body
- Trans-Neptunion Object
- an object in our solar system lying beyond the orbit of Neptune; abbreviated TNO
- transit
- the passage of a smaller body in front of a larger body; also, the passage of a celestial body across an observer’s meridian
- transparency
- the clarity of the sky
- Trapezium
- an open cluster of young stars, protostars, gas, and dust in the Orion Nebula featuring four prominent stars that form a trapezium
- tremolite
- a common mineral in some metamorphic rocks, composed mainly of calcium and magnesium; it occurs from the conversion of dolomite (a sedimentary rock), silica, and water
- trillion
- 1,000,000,000,000 (in American usage)
- Trojan
- an asteroid that lies in or near one of the Lagrange points 60 degrees ahead or behind Jupiter along the planet's orbit; Trojan asteroids have also been found accompanying Mars and Neptune