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15 Topic Pages Found in Science and starting with the letter U
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Open ultrasonics
ultrasonics

study and application of the energy of sound waves vibrating at frequencies greater than 20,000 cycles per second, i.e., beyond the range of human

Open ultraviolet astronomy
ultraviolet astronomy

study of celestial objects by means of the ultraviolet radiation they emit, in the wavelength range from about 90 to about 350 nanometers. Ultraviolet

Open ultraviolet radiation
ultraviolet radiation

invisible electromagnetic radiation between visible violet light and X rays; it ranges in wavelength from about 400 to 4 nanometers and in frequency

Open Ulysses (Spacecraft)
Ulysses (Spacecraft)

Ulysses was the first space probe to explore the region of space above the Sun's poles, as a joint project of the European Space Agency (ESA) and

Open Uncertainty Principle
Uncertainty Principle

physical principle, enunciated by Werner Heisenberg in 1927, that places an absolute, theoretical limit on the combined accuracy of certain pairs of

Open Underwater archaeology
Underwater archaeology

Underwater archaeology differs from terrestrial archaeology only in its requirements for different tools and techniques. Their aims are identical.

Open Uniformitarianism
Uniformitarianism

in geology, doctrine holding that changes in the earth's surface that occurred in past geologic time are referable to the same causes as changes now

Open universal time
universal time

(UT), the international time standard common to every place in the world, it nominally reflects the mean solar time along the earth's prime meridian

Open Ural Mountains
Ural Mountains

Mountain system extending for over 2,000 km/1,242 mi from the Arctic Ocean to the Caspian Sea, and traditionally regarded as separating Europe from

Open Uranus (Planet)
Uranus (Planet)

Seventh planet from the Sun, discovered by German-born British astronomer William Herschel in 1781. It is twice as far out as the sixth planet,