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From Space.com online
April 2012

The eighth and farthest planet from the Sun in the Solar System, the gas giant planet Neptune takes center stage in a series of sharp new photos snapped by the Hubble Space Telescope in honor of the blue-green world’s first Neptunian year around the sun since it was discovered in 1846.

On July 12, 2011 Neptune completed its first trip around the sun since being discovered nearly 165 Earth years ago — on Sept. 23, 1846, to be exact, by German astronomer Johann Galle.

Neptune takes about 165 years to complete one orbit around the sun. It is about 30 times farther from the sun than Earth and typically orbits at a distance of about 2.8 billion miles (4.5 billion kilometers).

Four new Hubble photos show Neptune in stunning detail. The images were taken about four hours apart and show the planet as it appeared between June 25 and 26 over the course of a single Neptunian day, which lasts about 16 hours, yielding a complete view of the distant world.

In a photo description, scientists said the new Hubble photos revealed more high-altitude clouds on Neptune than those seen in recent observations within the last few Earth years.

The clouds are composed of methane ice crystals and hover over parts of Neptune’s northern and southern hemisphere, Hubble scientists said.

Like Earth, Neptune spins on a tilted axis, which gives the planet its own set of seasons. Earth’s axis is tilted about 23 degrees, but Neptune has a more pronounced 29-degree tilt.

More about Neptune from Wikipedia:

Neptune is similar in composition to Uranus, and both have compositions which differ from those of the larger gas giants, Jupiter and Saturn. Neptune’s atmosphere, while similar to Jupiter’s and Saturn’s in that it is composed primarily of hydrogen and helium, along with traces of hydrocarbons and possibly nitrogen, contains a higher proportion of “ices” such as water, ammonia and methane. Astronomers sometimes categorize Uranus and Neptune as “ice giants” in order to emphasize these distinctions.

The interior of Neptune, like that of Uranus, is primarily composed of ices and rock. Traces of methane in the outermost regions in part account for the planet’s blue appearance.

In contrast to the relatively featureless atmosphere of Uranus, Neptune’s atmosphere is notable for its active and visible weather patterns. For example, at the time of the 1989 Voyager 2 flyby, the planet’s southern hemisphere possessed a Great Dark Spot comparable to the Great Red Spot on Jupiter. These weather patterns are driven by the strongest sustained winds of any planet in the Solar System, with recorded wind speeds as high as 2,100 km/h.

Because of its great distance from the Sun, Neptune’s outer atmosphere is one of the coldest places in the Solar System, with temperatures at its cloud tops approaching −218 °C (55 K). Temperatures at the planet’s center are approximately 5,400 K (5,000 °C).

Neptune has a faint and fragmented ring system, which may have been detected during the 1960s but was only indisputably confirmed in 1989 by Voyager 2.

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