planet Neptune in astronomy photo

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The planet Neptune in astronomy

Neptune from 4.4 million miles by Voyager 2, 1990, five days before closest approach.




The "Great Dark Spot" (GDS) at the center of the photograph of Neptune above is about 8100 miles by 4100 miles, longer than the Earth’s diameter. Bright clouds near the GDS are higher in altitude than the dark material within. The small, bright cloud near Neptune’s left limb known as "Scooter" rotates faster than the GDS, gaining about 30° in longitude every rotation. Dynamic weather patterns on Neptune can change significantly on timescales of one rotation—about l8 hours.  Neptune’s winds, at up to 1250 mph (1.6 times the speed of sound), are the fastest in the solar system, with storms the size of the Earth. How Neptune gets its weather is a mystery since the Sun, which is the engine that drives the weather on Earth, is 900 times dimmer on Neptune. These clouds were seen to persist for as long as Voyager's cameras could resolve them.

After Uranus’ 1781 telescopic discovery by William Herschel, it was noticed that its orbit was not obeying Newton’s laws. When it was conjectured that an as yet undiscovered more distant planet must be perturbing its orbit, many great minds set out to discover planet X. Neptune was discovered in 1846 near to the position predicted from calculations based on the positions of Jupiter, Saturn and Uranus.

Jupiter, Saturn, Uranus and Neptune are "gas giants": no surface to stand on, rapid rotation, a deep atmosphere, rings and lots of satellites. Neptune is 10 to 15% methane—giving it that lovely blue color—under a lighter atmosphere of hydrogen and helium. It likely has a small solid center about the mass of Earth. In 1999 a UC Berkeley physics student came up with a hypothesis as to why Neptune gives off 2.6 times as much heat as it gets from the Sun. She used a laser beam on some methane to create "pressure and heat conditions that you might find about a third of the way toward Neptune’s center." Under this extreme pressure the methane’s carbon atoms began binding to one another, forming diamond dust. If those conditions exist in the hot, crushing, methane-rich atmosphere of Neptune, it may be literally raining diamonds on Neptune, which then release friction heat as they fall. Neptune’s core could be a diamond as large as the Earth.

This Planet-Neptune-in-Astronomy page and much of this 600-page website are excerpted from the personalized Fine Art Book You and the Universe.

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© Carl Woebcke: The Planet Neptune in Astronomy, 1991-2017. All rights reserved.