V - W - X

Select the letter that (probably) leads off the word in question. Please suggest new words or corrections.

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V

• Van Allen radiation belts: The belt of radiation around the Earth that shields us from harmful rays emitted by the Sun.

• Venus: The second planet from the Sun. It is a rocky (solid) planet and is always shrouded in cloud cover. It is also known as the "morning star" or "evening star".

• variable star: A star that perceptibly changes its illumination. See "Cepheid variable".

• vernal equinox: A point in the sky where the celestial equator crosses the ecliptic and where the Sun is located on the first day of spring in the Northern Hemisphere. See "Celestial Equator".

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W

• white dwarf: A small, dense remnants of a sunlike star in its last phase of life. It shines from stored heat.

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X

• x-ray: A relatively high-energy photon with wavelength in the approximate range from 0.01 to 10 nanometers in the spectrum.

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