ASTEROID A rocky space object which can be from a few hundred feet to several hundred km wide. Most asteroids in our solar system orbit the Sun in a belt between Mars and Jupiter.

ASTRONOMER An expert in the study of the Sun, Moon, stars, planets, and other space bodies.

ASTRONOMICAL UNIT The approximate distance from the Sun to the Earth which is equal to 150,000,000 kilometers.

ASTROPHYSICS The branch of astronomy that deals with the physics of stellar phenomena.

ATMOSPHERE The layers of gases which surround a star, like our Sun, or a planet, like our Earth.

AXIS An imaginary straight line around which an object rotates.

BASALT A dark, fine-grained volcanic rock.

BIG BANG THEORY A theory which states that the Universe began to expand after a super powerful explosion of concentrated matter and energy.

BLACK HOLE The leftover core of a super massive star after a supernova. Black holes exert a tremendous gravitational pull.

CENTIGRADE See CELSIUS.

CHARGED PARTICLES electrons, protons, ions.

COMA A hazy cloud which surrounds the nucleus of a comet.

COMET Frozen masses of gas and dust which have a definite orbit through the solar system.

CORONA The very hot outermost layer of a star's atmosphere. Our Sun's corona can only be seen during a total solar eclipse.

COSMONAUT An astronaut from the former Soviet Union or the current republic of Russia.

COSMOLOGICAL Having to do with the study of the history, structure, and changes in the universe.

DENSITY The mass per unit of volume of a substance.

DOPPLER SHIFT A shift in an object's spectrum due to a change in the wavelength of light that occurs when an object is moving toward or away from Earth.

ELECTROMAGNETIC WAVE A wave of electric and magnetic energy that is generated when an electric charge is accelerated.

ELLIPTICAL Shaped like an elongated closed curve.

ENERGY Usable heat or power; in physics, it is the capacity of a physical system to perform work.

FUSION A nuclear reaction in which an element with small atoms fuses to form an element with larger atoms, releasing large amounts of energy.

GAMMA-RAYS Penetrating short wave electromagnetic radiation of very high frequency.

GEOSYNCHRONOUS An orbit in which a satellite's rate of revolution matches the Earth's rate of rotation. This allows the satellite to stay over the same site on the Earth's surface at all times.

GRAVITATIONAL FIELD The volume over which an object exerts a gravitational pull.

GRAVITATIONAL FORCE See Gravity

GRAVITATIONAL PULL See Gravity

GRAVITY The force of attraction between two objects which is influenced by the mass of the two objects and the distance between the two objects.

GYROSCOPE A heavy wheel or disk mounted so that its axis can turn freely in one or more directions. A spinning gyroscope tends to resist change in the direction of its axis.

HELIOCENTRIC Having the Sun as a center, such as a heliocentric solar system.

INFRARED WAVES Electromagnetic radiation with long wavelengths which is found in the invisible part of the spectrum. Human beings experience infrared waves as heat.

ION An electrically charged particle. Ions may be negatively or positively charged.

KILOGRAM 1000grams. A kilogram equals 2.2 pounds.

KILOMETER 1000 meters. A kilometer equals 0.6214 miles.

KILOPARSEC 1000 parsecs. A parsec equals 3.26 light years.

MANTLE The middle layer of a planet located between the crust, or surface, and the core.

MASS The measure of the amount of matter in an object.

MATTER Anything which has mass and occupies space.

METEOR Meteoroids which burn up in the atmosphere of a space body, such as the Earth, prior to impacting on the surface.

METEORITE Fragments of material that fall from space and impact on other larger space bodies.

METEOROID Fragments of material which vaporize when they have a close encounter with a space body which has an atmosphere.

METRIC TON 1000 kilograms. A metric ton equals 2,204 pounds.

MICROMETEOROID Very small pieces of matter which are encountered in space.

MICROWAVE Electromagnetic radiation which has a long wavelength (between 1 mm and 30 cm). Microwaves can be used to study the universe, communicate with satellites in orbit around Earth, and cook popcorn.

MYLAR A tough polyester material used as an insulator.

NEBULA A low density cloud of gas and dust in which a star is born.

ORBIT A specific path followed by a planet, satellite, etc.

PAYLOAD BAY The main body of the Space Shuttle where the payload, or cargo, is stored.

PHOTOSYNTHESIS The process by which plants use carbon dioxide, nutrients, and sunlight to produce food.

PHYSICIST A person who studies physics.

PHYSICS The science of matter and energy, and of interactions between the two. A person who studies physics is called a physicist.

PLAINS Vast, flat areas with low elevation.

PROBES Unmanned spacecraft which are launched into space in order to collect data about the solar system and beyond. Space probes are not necessarily designed to return to Earth.

QUASAR A distant energy source which gives off vast amounts of radiation, including radio waves and X-rays.

RETROGRADE Having a direction which is opposite that of similar bodies.

REVOLUTION The circling of a smaller object around a larger object.

ROTATION The spinning of an object on its axis.

SILICON A non-metallic chemical element.

SOLAR ECLIPSE A shadow which falls on an area of Earth when the Moon moves between the Sun and Earth.

SOLAR FLARES A magnetic storm on the Sun's surface which shows up as a sudden increase in brightness.

SOLAR PROMINENCES Gases trapped at the edge of the Sun which appear to shoot outward from the Sun's surface.

SOLAR SYSTEM The Sun and all of the planets, comets, etc. which revolve around it.

SOLAR WIND A continuous stream of charged particles which are released from the Sun and hurled outward into space at speeds up to 800 kilometers per second. Solar winds are very prominent after solar flare activity.

SOLAR WINGS A panel of solar cells which converts sunlight into electrical energy.

SPECTROGRAPH The image of the electromagnetic spectrum produced by a spectroscope.

SPECTROSCOPE An instrument which separates visible light into its various wavelengths. Each wavelength corresponds to a specific color in the spectrum.

SPECTRUM A band of colors which forms when visible light passes through a prism. The band ranges in color from violet (shorter wavelength) to red (longer wavelength).

SUNSPOT A magnetic storm on the the Sun's surface which appears as a dark area. A sunspot is approximately 1500 degrees Celsius cooler than it's surrounding material. The number of sunspots we see on the Sun at any given time appears to cycle every 11 years.

TELESCOPE Any of various devices, sometimes made with an arrangement of lenses, mirrors, or both, used to detect and observe distant objects by their emission, transmission, reflection, or other interaction with invisible radiation.

THERMOMETER An instrument for measuring temperature.

UNIVERSE The vast expanse of space which contains all of the matter and energy in existence.

The StarChild site is a service of the High Energy Astrophysics Science Archive Research Center (HEASARC), Dr. Alan Smale (Director), within the Astrophysics Science Division (ASD) at NASA/ GSFC.

StarChild Authors: The StarChild Team StarChild Graphics & Music: Acknowledgments StarChild Project Leader: Dr. Laura A. Whitlock Curator: J.D. Myers Responsible NASA Official: Phil Newman If you have comments or questions about the StarChild site, please send them to us.

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StarChild: Glossary