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Offline Maze

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Neptune's distance
« on: 30/03/2009 21:13:48 »
Neptune is about 30 AU from the Sun and has an elliptical orbit. When Neptune was first discovered they used trigonometry to determine this distance. But I am not sure how it is measured these days. Maybe one on the spacecraft that passed by Neptune may have given us todays distance. It may have been a radar technique but being so far out, I'm not sure this would have been feasible.
Can't find the answer on the internet. The answer would really be appreciated.


 

Offline Vern

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Neptune's distance
« Reply #1 on: 30/03/2009 22:03:10 »
I found this with a Google search. From the link I glean that they calculated the distance using data obtained by other means, but Voyager 2 data probably helped.

Quote from: the link
The Voyager 2 spacecraft was launched from Earth in 1977, and then flew by Jupiter in July 1979, Saturn in August 1981, and Uranus in January 1986. Uranus accelerated Voyager 2 toward a flyby of Neptune along a hyperbolic orbit in August 1989. The season on Neptune was late spring, nearly summer, in its southern hemisphere. The closest approach (18,169 mi [29,240 km]) to Neptune's center occurred at 3:56 Universal Time (U.T.) on August 25, 1989, about 4,900 km above the cloud tops of its north polar region. During Voyager 2's encounter with Neptune from June 5, 1989, to October 2, 1989, the observations it made greatly increased our knowledge about the Neptune system. The plane of Neptune's equator is tilted 29.6 to the plane of its orbit around the Sun. Voyager 2 flew by Triton at a minimum distance of 24,724 mi (39,790 km) on August 25, 1989 at about 9:10 U.T. It observed Triton continuously from about 6:00 U.T. to 12:00 U.T. on that date, and discovered much about Triton that will be discussed in detail in a separate section. The main discoveries Voyager 2 made about Neptune, its rings, and its small satellites follow.
 

Offline astrobabe

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Neptune's distance
« Reply #2 on: 31/03/2009 01:26:49 »
Neptune was discovered nearly 160 years ago meaning it has completed almost a full orbit since its discovery. There have been many, many observations of it since that date so we have a very accurate orbit, and more importantly orbital period. Given its orbital period it is easy to calculate its distance relative to the Earth-Sun distance (= 1 AU) by using Kepler's third law. Since both the Earth and Neptune are orbiting the same object, the Sun, their relative periods (PE for the Earth and PN for Neptune) give their relative distances (aE for the Earth, aN for Neptune) by:
               (PN / PE)2 = (aN / aE)3.
Thus:
               aN = aE (PN / PE)2/3.
I hope that helps!
 

Offline syhprum

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Neptune's distance
« Reply #3 on: 31/03/2009 10:27:41 »
Galileo made an early observation of Neptune but did not recognise it as a planet (probably just as well).

http://en.wikipedia.org/wiki/Neptune
 

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Neptune's distance
« Reply #3 on: 31/03/2009 10:27:41 »

 

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