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Neptune at Opposition

August 26, 2013

The giant planet Neptune is putting in its best showing of the year. It lines up opposite the Sun in our sky. It rises around sunset, is in the sky all night, and shines at its brightest. Even so, you still need good binoculars or a telescope to see it. It’s low in the southeast an hour or so after sunset, near the middle of the constellation Aquarius.

Neptune is the fourth-largest planet in the solar system — about four times the diameter of Earth. But it’s also the most distant planet — 2.8 billion miles from the Sun.

Like all the giant outer planets, Neptune has a thick, turbulent atmosphere. Jet streams at the top of the atmosphere blow at up to 650 miles per hour. They blow westward at the equator, and eastward at higher latitudes.

Winds and currents extend deep below the planet’s cloudtops before eventually giving way to a steady layer of compressed hydrogen and helium. But just how deep the turbulent atmosphere extends has been a puzzle. But planetary scientists at the University of Arizona recently said they have the answer.

Neptune’s atmosphere is so dense that large-scale motions create subtle changes in the planet’s gravitational field. The researchers examined measurements of that field made decades ago by the Voyager 2 spacecraft. A detailed study says the moving atmosphere extends only about 600 miles below the cloudtops — a relatively thin blanket of “air” atop one of the solar system’s giants.


Script by Damond Benningfield, Copyright 2013

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