Astro Glossary

  • UFOs

  • Ultraviolet Astronomy

    A wavelength, or frequency, of light that is more energetic than visible light, but less energetic than x-ray radiation. Ultraviolet, or UV, radiation ranges in wavelength between 10^-8 and 10^-7 meters and in frequency between 10^15 and 10^17 Hz. UV rays can be very harmful to life because they are strong enough to ionize atoms and destroy cells. Fortunately, the Earth’s atmosphere shields us from most UV radiation. Astronomers who want to study UV light from celestial sources must do so from space-borne telescopes, such as the Hubble Space Telescope.

  • Unified Theory

  • Uranus

    The seventh planet from the Sun in the solar system. Uranus orbits the Sun at an average distance of 19.2 AU. The planet has a mass 14.5 times the mass of Earth and a radius 4.0 times the radius of Earth. Uranus is a gas planet made of hydrogen, helium, and methane and has no solid surface. The planet’s axial tilt is an extreme 98 degrees, causing one year on Uranus to equal 84 years, equal to the time it takes Uranus to orbit the Sun once.

  • Uranus' Moons

    Uranus has 17 known moons, the largest of which are Titania and Oberon.

  • Ursa Major, the Great Bear

    A constellation always visible from northern latitudes, containing the stars of the Big Dipper.

  • Ursa Minor, the Lesser Bear

    A constellation containing the stars of the Little Dipper and Polaris, the North Star.

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