The Bigger Blue Marble


Neptune is the eight and farthest planet from the Sun, yet its internal energy is sufficient to drive the fastest planetary winds seen in the Solar System.

Fourth-largest planet by diameter and the third-largest by mass.

This was the only planet found by mathematical prediction.

Astronomers couldn't understand why Uranus didn't match orbit predictions. The other planets had there orbits predicted correctly. Finally it was suggested that possibly another large body was pulling Uranus back by gravity.

Several predictions were made and Johann Galle found the planet within one degree of the prediction of Urbain Le Verrier. This was on September 23, 1846.

In early October, the largest moon, Triton was discovered by William Lassell. Triton is the only regular moon in the solar system with a retrograde orbit. This means it orbits opposite the direction of orbit from the parent planet.

This planet is so far from the Sun it takes almost 165 years to complete an orbit. The first full orbit since discovery happened on July 11, 2011... 164 years and 10 months.

A Neptunian day is about 16 hours long.

The planet tilts on its axis slightly more than Earth so it has seasons like we do here. The difference is that a season there last forty years as opposed to our three months.

There are active weather patterns including the various Dark Spots. These are storms in the atmosphere similar to the Great Red Spot of Jupiter. These storms appear and disappear though over time.

Neptune and Triton

Unfortunately you won't be able to see them as the planet is too far away and reveals no details to amateur scopes.

As an 8th magnitude object you can't see it without visual aid.

A telescope or strong binoculars will resolve Neptune as a small blue disk, similar in appearance to Uranus. The large moon Triton is visible as a point of light in larger size scopes...with at least an eight inch(200mm) diameter.

Orion SkyQuest XT8 PLUS Dobsonian Reflector Telescope

The blue color, as with Uranus, is caused by methane gas in the atmosphere. Methane scatters red light while allowing the blue light through.

Like the other outer planets, there is a ring system-though it's very sparse and not impressive, and many natural satellites. 14 moons orbit the planet but you should only look for Triton. The rest are rather small irregulars and not visible to amateur telescopes.

Every 367 days as Earth passes Neptune in orbit, it appears to move backwards in the sky. This looks like a loop to us.

close-up Neptune atmosphere
› Neptune
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