Neptune




   Neptune is the second to the last of the planets. In some cases Neptune is the farthest of the planets from the sun. Neptune and pluto cross orbits twice in a rotation around the sun. One of these switches puts Neptune farther and one puts Neptune closer then Pluto. Most of the time Neptune is closer but during that 1 month (Earth time) Neptune is the farthest planet out.

   Neptune is the outermost planet of the gas giants. It has an equatorial diameter of 49,500 kilometers (30,760 miles). If Neptune were hollow, it could contain nearly 60 Earths. Neptune orbits the Sun every 165 years. It has eight moons, six of which were found by Voyager. A day on Neptune is 16 hours and 6.7 minutes. Neptune was discovered on September 23, 1846 by Johann Gottfried Galle, of the Berlin Observatory, and Louis d'Arrest, an astronomy student, through mathematical predictions made by Urbain Jean Joseph Le Verrier.

   Neptune is a dynamic planet with several large, dark spots reminiscent of Jupiter's hurricane-like storms. The largest spot, known as the Great Dark Spot, is about the size of the earth and is similar to the Great Red Spot on Jupiter. Voyager revealed a small, irregularly shaped, eastward-moving cloud scooting around Neptune every 16 hours or so. This scooter as it has been dubbed could be a plume rising above a deeper cloud deck.


Neptune Statistics
 Discovered byJohann Gotfried Galle 
 Date of discoverySeptember 23, 1846 
 Mass (kg)1.024e+26 
 Mass (Earth = 1)1.7135e+01 
 Equatorial radius (km)24,746 
 Equatorial radius (Earth = 1)3.8799e+00 
 Mean density (gm/cm^3)1.64 
 Mean distance from the Sun (km)4,504,300,000 
 Mean distance from the Sun (Earth = 1)30.0611 
 Rotational period (hours)16.11 
 Orbital period (years)164.79 
 Mean orbital velocity (km/sec)5.45 
 Orbital eccentricity0.0097 
 Tilt of axis (degrees)28.31 
 Orbital inclination (degrees)1.774 
 Equatorial surface gravity (m/sec^2)11.0 
 Equatorial escape velocity (km/sec)23.50 
 Visual geometric albedo0.41 
 Magnitude (Vo)7.84 
 Mean cloud temperature-193 to -153°C 
 Atmospheric pressure (bars)1-3 
 Atmospheric composition
Hydrogen
Helium
Methane

85% 
13% 
2% 


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