Neptune - Known Facts

About Neptune, what scientific facts are known including trivia about the orbit, surface, and more.



Known Facts: Because Uranus deviated from its calculated orbit, astronomers suspected another planet. Between 1843 and 1845, John Couch Adams, a graduate of Cambridge, calculated the orbit of this unseen body and sent his findings to Sir George Airy, Britain's royal astronomer, who ignored them.

Urbain Leverrier, a well-known French astronomer, also calculated the orbit and published his work on July 1, 1846. He predicted the planet's position and said it would show a discernible disk. So convinced were astronomers by now that Sir John Herschel, son of the discoverer of Uranus, proclaimed, "We see it as Columbus saw America from the shores of Spain."

Airy noticed that Leverrier's results resembled those of Adams, so he asked the British astronomer James Challis to search. Challis did, leisurely compiling a star map the while, and observed the planet twice without recognizing it. He even noted that the "star" looked like a disk.

Leverrier couldn't interest the French in searching, so he wrote to Johann Galle, a young, enthusiastic astronomer in Berlin, who, with Heinrich d'Arrest, discovered Neptune on Sept. 23, 1846, within a half-hour of beginning observations. The discovery was announced on Sept. 25.

British astronomers were outraged when Airy's incompetence became public. Both Adams and Leverrier are now credited with predicting Neptune's position.

Neptune appears a small, greenish-blue disk when viewed through a telescope. Because it is invisible to the naked eye, it is termed an "outer planet." Because it is large and has low density, it ranks as "Jovian." The planet is very similar to, but slightly smaller and more massive than, Uranus. Its gravitational field is strong enough to hold an atmosphere, predominantly methane, with some hydrogen, acetylene, and possibly ammonia. The core may be rocky and earthlike. Recent observations have determined its diameter to be about 30,000 mi.

Neptune has been increasing in brightness since 1972. Some astronomers speculate that this indicates gigantic storms on the planet. It emits radiation similar to that coming from Uranus, Jupiter, and Saturn.

In 2011 A.D., Neptune will complete its first orbit since discovery. It is now the outermost planet, Pluto being closer to us until 2009 A.D. It is so distant that it takes light from the sun over four hours to reach its surface. Since NASA's Grand Tour was canceled, no space probe is planned for Neptune.

Two moons, Triton and Nereid, circle the planet. Triton, discovered within a month after Neptune, is larger than our moon and closer to Neptune than our moon is to Earth. It moves fast, orbiting Neptune in 5.88 days in a retrograde direction. Nereid is quite different, a small rock about 200 mi. in diameter. Its orbit is the most eccentric of any satellite, skewed out of plane, and requiring almost 360 days to complete. It is possibly a captured asteroid.

Halley's Comet may be one of the family of comets associated with Neptune. At least eight are known.

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