[Athena] [Curriculum] [Space]
Glossary of Terms -
Space Science

courtesy of JPL

[ A, B, C, D, E, F, G, H, I, J, K, L, M, N, O, P, Q, R, S, T, U, V, W, X, Y, Z ]

A Active Sun - The Sun during times of frequent solar activity such as sunspots, flares, and associated phenomenon
Aimpoint - The point in the planet's plane that spacecraft aim for to either fly by or enter orbit.
Albedo - Reflectivity; the ratio of reflected light to incident light. The fraction of sunlight that a body reflects.
Alpha Centauri - The closest bright star.
Anticyclonic - Description of the sense of rotation of an atmospheric spot or storm; anticyclonic motion is clockwise in the northern hemisphere and counterclockwise in the southern hemisphere; it suggests a high pressure region.
Antimatter - matter consisting of antiparticles such as antiprotons, antielectrons (positrons), and antineutrons.
Aperture - The diameter of an opening; the diameter of the primary lens or mirror of a telescope.
Aphelion - The point in orbit where a body is farthest from the Sun.
Apex - The point towards which a body is moving.
Apoapsis - High point of an orbit.
Apogee - The point in orbit where a body is farthest from Earth.
Asteroid Belt - A 1/2-AU-wide region between the orbits of Mars and Jupiter where the most asteroids are found.
Astrophysics - That part of the astronomy dealing with the physics of astronomical objects and phenomena.
AU - Unit of distance, equal to the distance of the Earth from the Sun, about 150 million kilometers (93 million miles).
Aurora - Light radiated by ions and atoms in the Earth's upper atmosphere, mostly in polar regions.
Azimuth - Motion around a vertical axis; for instance, a measure of position around the horizon.
B Backscattering - Reflecting light back in the direction of the source.
Bar - Unit of pressure (short for atmosphere), equal to the sea-level pressure of Earth's atmosphere.
Basin - A large, >200 km (124 miles), circular depression from the explosive impact of an asteroid or similar sized body on a planet surface, usually rimmed by mountains.
Big Bang Theory - The theory that the universe was once clustered and at the 'beginning' it exploded out, as shown by the fact that objects are still moving out from the center.
Black hole - An object whose gravity is so strong that the escape velocity exceeds the speed of light.
Blue moon - The occasional blue color seen in the moon due to the Earth's atmosphere.
Bow Shock - Outermost part of a planetary magnetosphere; the place where the supersonic flow of the solar wind is slowed to subsonic speed by the planetary magnetic field.
C Calibration - Setting an measuring instrument before measuring for accurate results.
Centrifugal force - The apparent outward force felt by a body rotating about an axis.
Charon - The only known satellite of Pluto.
Comet - A small body of ice and dust in orbit around the Sun. While passing near the sun, a comet's vaporized ice become its "tail"
Constellation - A group of stars that make a shape, often named after mythological characters, people, animals, and things.
Convection - Rising warm air and falling cool air. The transfer of energy by moving currents of fluid or gas containing energy.
Core - The innermost layer of a planet or star.
Corona - The Sun's outer atmosphere.
Co-rotating - Sharing the rotation of a planetary magnetic field, as in a co-rotating plasma.
Cosmic year - The time it takes the Sun to revolve around the center of the galaxy, approximately 225 million years.
Crater - A round impression left in a planet or satellite from a meteoroid.
Crust - The outer layer of Earth and other terrestrial planets.
Cyclonic - Circular wind motion in a planets atmosphere, counter clockwise in northern hemisphere.
D Dark matter - A form of matter which has not been directly observed but whose existence has been deduced by it's gravitational effects.
Density - The mass to volume ratio, a measure of how much matter an object has for its size.
Density Wave - A kind of wave induced in a flat plane of a resisting medium (such as the rings of Saturn) by gravitational forces, often assuming the form of a tightly wound spiral.
Downlink - A radio connection intact wherein a spacecraft can communicate to Earth.
E Eccentric - Noncircular; elliptical (applied to an orbit).
Eclipse - The cutting off of light from one celestial body by another.
Elevation - Motion around a horizontal axis; opposite to azimuth.
F Fault - A crack or break in the crust of a planet along which slippage or movement can take place.
Fault protection - A program built into a spacecraft which detects errors and faults in the spacecraft before they become monstrous and fixes them or reroutes to avoid them.
Forward Scattering - Reflecting light approximately away from the source.
G Geocentric - Earth centered.
Galaxy - A large group of stars; The galaxy of which the nearby starsand Sun are members.
Gravity - A mutual physical force attracting two bodies.
Great Red Spot - A huge anticyclonically rotating meteorological eddy on Jupiter.
H Halley's comet
A bright comet, visible to the naked eye, whose path we can predict.
Helio- - Prefix referring to the Sun.
Heliocentric - Centered on the Sun.
Hyperbolic - A trajectory path to a planet shaped like a hyperbola.
I IAU - International Astronomical Union
Imbedded Satellite - A postulated class of satellites orbiting inside the rings, searched for but not found.
Inclination - Of an orbit, The angle between the orbital plane of arevolving body and some fundamental plane, usually the plane of the celestial equator.
Infrared - Electromagnetic radiation whose wavelength is longer than the longest visible red but shorter than radio waves.
Interferometery - The location and examination of sources of electromagnetic radiation through the simultaneous use of two or more separated telescopes. Interferometers produce overlapping wave patterns from the radiation. These patterns are studied to determine the brightness and angular structure of the emitting source.
Ion - An atom or molecular fragment that has a positive electrical charge due to the loss of one or more electrons. The simplest ion is the hydrogen nucleus, a single proton.
IRIS - The Infrared Interferometer Spectrometer, one of the Voyager instruments.
J Jet Propulsion - The engine moves forward by reacting to the momentum of air of gaseous material being forced out of the back of the engine.
Jovian Planet - Any of the four biggest planets: Jupiter, Saturn, Uranus, and Neptune.
L Lagrangian Point - One of the solutions to the three-body problem discovered by the eighteenth century French mathematician Lagrange. The two stable Lagrangian points, L-4 and L-5, lie in the orbit of the primary body, leading and trailing it by a 60-degree arc. Jupiter's trojan asteroids can be found orbiting around the Jupiter-Sun L4 & L5 points.
Leading Side - For a satellite that keeps the same face toward the planet, the hemisphere that faces forward, into the direction of motion.
Light - Electromagnetic radiation that is visible to the eye.
Light year - The distance light travels in a vacuum in one year.
Lunar - Referring to the moon.
M Magnetic field - A region of space near a magnetized body where magnetic forces can be detected.
Magnetopause - The boundary of the magnetosphere, Lying inside the bow shock.
Magnetosphere - The region surrounding a planet within which the planetary magnetic field dominates and charged particles can be trapped.
Mantle - Middle layer of the Earth; between the crust and the core.
Mass - The measure of the amount of matter in an object. The mass of an object is different from but proportional to it weight.
Mean - Synonym for average.
Meteor - The luminous phenomenon seen when a meteoroid enters the atmosphere, commonly known as a shooting star.
Meteorite - A part of a meteoroid that survives through the Earth's atmosphere.
Meteoroid - A small rock in space.
N Newton - A unit of force that is a size such that a body of one kilogram under it effects would accelerate one meter per second per second.
O Orbit - The path of an object that is moving around a second object or point.
P Periapsis - Low point of an orbit.
Period of revolution - Time of one complete cycle in orbital motion - referred to as a year when applied to Earth.
Period of rotation - Time of one complete cycle - referred to as a day when applied to Earth.
Perturbation - A small disturbing effect
Phase angle - The angle in which waves come to a body.
Photometry - The measurement of light intensities.
Plasma - A low-density gas in which the individual atoms are charged, even though the total number of positive and negative charges is equal, maintaining an overall electrical neutrality.
Plasma Wave - An oscillation or wave in a plasma that falls in the audio range of frequency.
Primitive - Used in a chemical sense, indicating an unmodified material representative of the original composition of the solar nebula.
R Rj - Unit of distance equal to the radius of Jupiter, 71398 km (44365 miles)
Rs - Unit of distance equal to the radius of Saturn, 60,300 km (37,469 miles)
Radiation - Electromagnetic energy, photons
Radiometry - The detection and measurement of radiant electromagnetic energy, usually in the infrared. The radiometer on theMagellan spacecraft, for instance, measured the thermal radiation of the surface of Venus from orbit.
Radiation Belts - Regions of charged particles in a magnetosphere; the belts contain ions and electrons.
Resolution - Ability to distinguish visual detail, usually expressed in terms of the size (in kilometers) of the smallest features that can be distinguished. (Here resolution is given in kilometers per line pair.)
Resonance - A relationship in which the orbital period of one body is related to that of another by a simple integer fraction, such as 1/2, 213, 3/5.
Retrograde - Backwards; as applied to an orbit, moving in the opposite sense from the great majority of solar system bodies.
Revolution - Movement of a planet around the Sun; more generally, orbital motion about a point.
Rotation - Turning of a body on its axis.
S Satellite - A body that revolves around a larger body.
Scan Platform - The part of the Voyager spacecraft that carries the imaging, IRIS, ultraviolet, and photopolarimeter instruments. It can be pointed to any part of the sky by rotating around two axes (azimuth and elevation).
Scatterometry - This reads bounced radar waves to measure the winds over the ocean. NSCAT, (NASA Scatterometer) will use an array of stick-like antennas that radiate microwave pulses across broad regions of the Earth's surface. The radar pulses are reflected back and NSCAT's antennas capture the returned pulses as it orbits about 800 kilometers (500 miles) high in space. The processed information is transmitted to receiving stations on Earth.
Sequence - A series of commands stored in the Voyager computers containing instructions for operation of the scan platform and the scientific instruments; also, the resulting observations themselves.
Shepherd - Informal name applied to a satellite orbiting very close to a ring and thought to cause a gravitational focusing that keeps the ring particles from drifting in the direction of the shepherd satellite.
Solar Nebula - The large cloud of gas and dust from which the Sun and planets condensed 4.6 billion years ago .
Solar Wind - The charged particles (plasma), primarily protons and electrons, that are emitted from the Sun and stream outward throughout the solar system at speeds of hundreds of kilometers per second.
Spectroscopy - The use of spectrum analysis.
Spectrum - A particular distribution of wavelengths and frequencies.
Spokes - Informal name given to the transitory radial features in the B Ring, appearing dark when seen in backscattered light and bright in forward scattered light.
Stratosphere - The cold region of a planetary atmosphere above the convecting regions (the troposphere), usually without vertical motions but sometimes exhibiting strong horizontal jet streams.
T Telemetry - Radio signals from a spacecraft used to encode and transmit data to a ground station.
Terrestrial Planet - Any of the four planets closest to the Sun: Mercury, Venus, Earth, Mars.
Torus - Solid geometrical figure with the shape of a doughnut or innertube, as in the toroidal hydrogen cloud surrounding Saturn near the orbit of Titan.
Trailing Side - For a satellite that keeps the same face toward the planet, the hemisphere that faces backwards, away from the direction of motion.
Troposphere - The lower regions of a planetary atmosphere where convection keeps the gas mixed and maintains a steady increase of temperature with depth. Most clouds are in the troposphere.
U Ultraviolet - Radiation shorter than visible light but longer than X-rays.
V Volcano - An opening in the Earth's crust that allows magma to reach the surface.
Volcanism - Volcanic force or activity.


Selected Bibliography:

Considine, Douglas M., ed., "Van Nostrand's Scientific Encyclopedia." 5th ed., New York, Van Nostrand Reinhold Company, 1976
Kaufmann, William J. III, "Discovering the Universe." New York, W.H. Freeman and Company, 1987
Moore, Patrick, ed., "The International Encyclopedia of Astronomy." New York, Orion Books, 1987
Stockley, Corinne, and Oxlade, Chris, and Wertheim, Jane, "The Usborne Illustrated Dictionary of Science." Oklahoma, EDC publishing, 1988

Credits:

Glossary courtesy of of
NASA's Jet Propulsion Laboratory

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Last Modified Wed Nov 06 16:51:20 1996