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Lowell, Percival

(Encyclopedia)Lowell, Percival, 1855–1916, American astronomer, b. Boston, grad. Harvard, 1876; brother of Abbott Lawrence Lowell and Amy Lowell. He visited Korea and Japan, where he acted as counselor and foreig...

space probe

(Encyclopedia)space probe, space vehicle carrying sophisticated instrumentation but no crew, designed to explore various aspects of the solar system (see space exploration). Unlike an artificial satellite, which is...

Commoner, Barry

(Encyclopedia)Commoner, Barry, 1917–2012, American biologist, educator, and activist, one of the founders of the modern environmental movement, b. Brooklyn, N.Y., grad. Columbia (B.A., 1937), Harvard (Ph.D., 1941...

Ganymede, in astronomy

(Encyclopedia)Ganymede gănˈēmēdˌ [key], in astronomy, one of the moons, or natural satellites, of Jupiter; the largest natural satellite in the solar system, it is larger than the planet Mercury. ...

retrograde motion

(Encyclopedia)retrograde motion, in astronomy, real or apparent movement of a planet, dwarf planet, moon, asteroid, or comet from east to west relative to the fixed stars. The most common direction of motion in the...

evening star

(Encyclopedia)evening star or morning star, planet that becomes visible in the western sky shortly after sunset or in the eastern sky shortly before sunrise. It can usually be seen in twilight, when it is too light...

Ptolemaic system

(Encyclopedia)Ptolemaic system tŏlˌəmāˈĭk [key], historically the most influential of the geocentric cosmological theories, i.e., theories that placed the earth motionless at the center of the universe with a...

Eris, in astronomy

(Encyclopedia)Eris, in astronomy, the largest known dwarf planet. Eris, whose highly eccentric elliptical orbit ranges from 38 AU to 97 AU and is inclined more than 44°, is the largest known object of the Kuiper b...

Phoebe, in astronomy

(Encyclopedia)Phoebe fēˈbē [key], in astronomy, one of the named moons, or natural satellites, of Saturn. Also known as Saturn IX (or S9), Phoebe is 137 mi (220 km) in diameter, orbits Saturn at a mean distance ...

Anthropocene

(Encyclopedia)Anthropocene Epoch, an unofficial term used by scientists to describe a period of time—up to the present—in which humanity has impacted the planet on a global scale. The phrase was fir...