Neptune at Opposition: Seeing the Ice Giant, and What Voyager 2 and Hubble Found

Neptune is invisible to the naked eye, yet scientists would love to see it more clearly. Once a year, Earth passes directly between Neptune and the Sun, an event called opposition, and sky watchers and astronomers get the opportunity to observe it. When this NASA ScienceCast was made, opposition was on the night of September 9.

How to find it

Near opposition Neptune reaches its highest point in the sky around midnight, so evenings in September were the best time to look. You need a telescope or high-powered binoculars, and a sky chart or sky-watching software. The planet is 30 times farther from the Sun than Earth is, and in most amateur telescopes it is only a dot.

What the dot is

Neptune is an ice giant, a planet of monster storms. Its thick atmosphere is made of massive amounts of hydrogen and helium with traces of other gases. Under it lies a solid interior of rock and, deep below the clouds, a warm mantle of dense fluid.

What Voyager 2 and Hubble showed

That year's opposition came just after the 30th anniversary of the Voyager 2 flyby in 1989. Voyager 2 passed about 3,000 miles, or 5,000 kilometers, above Neptune's north pole and gave the closest look we have. Its pictures showed weather in the extreme, including a dark, violent vortex that looked like Jupiter's Great Red Spot.

Since then observatories such as the Hubble Space Telescope have watched from afar and shown that, unlike Jupiter's, Neptune's vortex disappears for a time, and similar storms appear later. Scientists have also found that Neptune has seasons like Earth's, but lasting decades, not months. Tracking them continually should help scientists compare atmospheres on other planets, including Earth's.

Sources

• NASA, NASA ScienceCasts: Eye on Neptune, NASA Image and Video Library (a Science@NASA video); rewritten in hubnx's own words.