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WANING Waning means shrinking in size.

WATER CYCLE The Water Cycle (also known as the hydrologic cycle) is the journey water takes as it circulates from the Earth to the sky and back again.

WATT A watt is a unit of power equal to one joule of energy per second. The watt was named for the Scottish engineer and inventor James Watt (1736-1819).

WAVE A wave is an energy-carrying disturbance that moves through space. Some examples of waves are waves in water, sound waves, and light waves.

WAVE FUNCTION A wave function (also called Schrodinger's Equation) is a differential equation in quantum theory that mathematically describes probability density of an object in space and time.

WAVELENGTH Wavelength is a characteristic of electromagnetic radiation. It is the distance between two wave crests.

WAXING Waxing means growing in size.

WEATHER Weather is the state that the atmosphere of a planet is in, like how hot or cold it is, or if there is precipitation (like rain).

Celestial Body Gravitation Factor Relative to Earth Sun 27.9 Mercury 0.38 Venus 0.91 Earth 1 Moon 0.17 Mars 0.38 Jupiter 2.54 Saturn 1.08 Uranus 0.91 Neptune 1.19 Pluto 0.6 WEIGHT Weight is a measure of how heavy something is. Weight is caused by the force of gravity pulling down upon an object. An object's weight depends on what planet or moon it's on (unlike mass, which is constant).

WEIGHTLESSNESS Weightlessness (or free fall) is the state in which an object appears to have no weight (but the object's mass remains the same). During weightlessness, an object's gravitational pull is negligible (close to zero). See microgravity.

WHITE, EDWARD H. Edward Higgins White II (1930- 1967) was an American astronaut and Air Force test pilot. He was the first American to walk in space; he was also the first person to use jet propulsion to maneuver himself in space while on a spacewalk. This spacewalk occurred on June 3, 1965, on the four-day Gemini 4 (GT-4, commanded by Jim McDivitt) mission, which circled the Earth 62 times. White was later chosen to be the senior Pilot for the first Apollo mission (Apollo 1). Lieutenant Colonel White died on January 27, 1967, during an Apollo training session (in which they were practicing emergency procedures). A flash fire quickly burned the spacecraft, killing White and his fellow astronauts, Gus Grissom and Roger Chaffee.

WHITE DWARF A white dwarf is a small, very dense, hot star near the end of its life. It is made mostly of carbon. These faint stars are what remains after a red giant star loses its outer layers. Their nuclear cores are depleted. They are about the size of the Earth (but are heavier). Our Sun will someday turn into a white dwarf. The companion of Sirius is a white dwarf.

WHITE GIANT A white giant is a rare, huge white star of spectral type A.

WHITE SUPER GIANT A white super giant is a rare, enormous white star of spectral type A. Deneb is a super white giant.

WHITE HOLE A white hole is the time reversal of a black hole, another singularity in space-time. Matter emerges unpredictably from a white hole (unlike a black hole, into which matter is drawn). An example of a white hole is the original singularity of the Big Bang.

WHITE OVAL OF JUPITER Jupiter's white oval is a 70-year-old storm. This enormous hurricane is almost the size of the Earth.

Comet Wild 2 Comet Wild 2 (aka Comet 81P) is the first comet that has been visited by a spacecraft. NASA's Stardust Mission rendezvoused with comet Wild 2 in January, 2004. The spacecraft will return to Earth on January 15, 2006. Comet Wild 2 is a short-period comet that was discovered by the Swiss astronomer Paul Wild on January 6, 1978. The comet's nucleus is about 3 miles (5 km) across. Wild 2 orbits the Sun every 6.39 years; its elliptical orbit ranges from about Mars' orbit to Jupiter's orbit.

WIMP WIMP stands for "Weakly Interacting Massive Particles." They are hypothetical particles that have a non-zero mass and only participate in weak nuclear interactions. Dark matter may be composed of WIMP's.

WIND Wind is the movement of atmospheric air on a planet. The wind is caused by the different temperatures (and therefore air pressure differences) around a planet - this is caused by the Sun. Other causes of the wind are the temperature differential over the land and over seas, the topography of the land (hills, mountains, plains, etc.), and the rotation of the Earth (which causes the Coriolis force). Air moves from areas of high pressure to aras of low pressure.

WINTER SOLSTICE The solstices are the days when the Sun reaches its farthest northern and southern declinations. The winter solstice occurs on December 21 and marks the beginning of winter (this is the shortest day of the year) in the Northern Hemisphere. The summer solstice occurs on June 21 and marks the beginning of summer (this is the longest day of the year) in the Northern Hemisphere.

WOLF-RAYET STARS Wolf-Rayet (W-R) stars are unusual stars that is very massive (over 40 times the mass of our Sun), extremely hot and very bright. These stars continually eject their outer atmosphere in bubble-like shells of particles and gas (and creating a strong stellar wind). About 200 of these stars are known in the Milky Way; most of these are very far from us. The W-R star closest to us is the double star gamma Velorum (in the constellation Vela). Wolf-Rayet stars were discovered in 1867 by C. J. Wolf and G. Rayet (at the Paris Observatory).

WORMHOLE A wormhole in space (also known as a Einstein-Rosen Bridge, named for Albert Einstein and Nathan Rosen) is a mathematical solution to Einstein's theory of General Relativity. A Lorentzian wormhole would theoretically provide a shortcut through widely-separated parts of space-time, through a black hole and out of a white hole (moving faster than the speed of light). Many physicists believe that wormholes have no physical reality because wormholes require "exotic matter," matter which is repelled by gravity (rather than attracted by it). John A. Wheeler coined the term wormhole in the mid 1950s.

WRIGHT, THOMAS Thomas Wright (1711-1786) was a British cosmologist. Wright was one of the first people (along with Johann Lambert (1728-77) and Immanuel Kant (1724-1804) ) who, in 1750, speculated about the structure and origin of our solar system and galaxy. Using religious and philosophical arguments, Wright hypothesized that the Milky Way was a thin flat system of stars with our solar system near the center and that there were other similar but distant star systems (which he called nebulae).