Glossary

Glossary: U through Z

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

U

Universe
The sum total of all existing things.

For more about the Universe, please see the big bang cosmology primer.

Uranus
The seventh planet from the Sun, Uranus is a gas giant planet with at least seventeen moons. It is also well known because of its peculiar axis of rotation, which is almost parallel to the ecliptic. Check out SEDS' Nine Planets, for more about Uranus. Or see StarDate's Solar System Guide.

Uranus

V

Venus
Venus has an orbit of 108 million km. It is the second planet from the Sun. Venus is very similar to Earth in many ways: both have roughly the same diameter and mass, both are terrestrial Planets and both have the same chemical make-up. Check out SEDS' Nine Planets, for more about Venus. Or see StarDate's Solar System Guide.

Venus

Vernal Equinox
The place in the sky where the Sun crosses the celestial equator moving northwards. The vernal equinox falls on, or near, March 21, the first day of spring. See celestial sphere for a helpful diagram.

VMOs
An acronym for Very Massive Object, VMOs are dark matter candidates which are thought to be 100 times more massive than our Sun. They are likely to be found in the form of black holes.

W

WIMP
An exotic class of non-baryonic particle, WIMPs (Weakly Interacting Massive Particles) are a prime dark matter candidate. For more about dark matter and WIMPs, check out these pages:

  • The question of dark matter
  • The WIMP experiment
  • Big bang cosmology primer

    Winter Solstice
    The point on the ecliptic where the Sun is farthest south. The winter solstice, which is the shortest day of the year, occurs on, or near, December 21, and marks the first day of winter. See celestial sphere for a helpful diagram.

    X

    X-Ray
    A class of high energy photon, X-rays have wavelengths of 0.012 to 12 nanometers. Not only are X-rays used for medical imaging (when you break your arm an X-ray machine is used to take a picture of the broken bone), but since black holes, quasars, and other stellar objects emit X-rays, X-Ray Astronomy is actively researched.

    X-Ray Astronomy
    A branch of astronomy which deals primarily with X-Rays.

    Y

    Year
    The period required for an object to orbit a star once. Note that the length of a year depends upon where you are: an Earth year is 365 days, but a Pluto year is almost 250 Earth years.

    Z

    Zenith
    The point on the celestial sphere which is directly above the observer.

    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


    Last modified: 1/15/1998, by Paul Shestople
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