If you want to see Neptune and you can get yourself to a telescope, tonight’s the night.
We have only one decent photo of Neptune, the furthest planet from the Sun. It was taken by the Voyager 2 probe, which visited in 1989 on the last stop of its Grand Tour. It had previously flown by Jupiter, Saturn and Uranus, and while the first two have been visited since by various orbiters, Uranus and Neptune have been left alone. Is it time to go back to the ice giants on the edge of the solar system?
Neptune at opposition 2018
Neptune reaches what astronomers call ‘opposition’ tonight, Friday, September 7, 2018. It’s an annual event when Earth is precisely between Neptune and the Sun. That means Neptune and Earth are as close as they ever get, and the ice giant gets the full glare of the Sun as seen from Earth, so it’s as bright as it ever gets. Its position opposite the Sun as seen from the Earth also means by definition that it’s visible all night long.
How to see Neptune
However, it can’t be seen with the naked eye; since it’s 4.5 billion km from the Sun (Earth is just 150 million km), it’s very small. To see it, point a telescope at Neptune (here’s exactly where to point it) and you will see a very obviously blue object.Since it orbits around the Sun very slowly (one year on Neptune equates to 165 Earth years), the eighth planet takes many years to move significantly in the night sky. It will be in the constellation of Aquarius until the 2020s. To see something so far out in the solar system – 4.5 billion km from the Sun compared to out own 150 million km – is a special sight indeed. For planet-hunters and stargazers, Neptune is worth seeing if only to check-off a list of solar system targets.
What do we know about Neptune?
It’s blue because the methane in its upper atmosphere reflects blue light. Voyager 2 photographed six rings around Neptune. It rotates once every 16 hours. It has a rocky core covered in ice and frozen methane and ammonia. It’s really windy, and despite seeming rather featureless, super-storms called Great Dark Spots have been spotted, most recently by the Hubble Space Telescope. The Very Large Telescope in Chile just took a look at Neptune.
What do we know about Triton?
Neptune may prove to be less interesting than the largest of its moons, Triton. From the images of Triton sent back by Voyager 2, it’s possible that Triton has ice volcanoes, active volcanoes that erupt like geysers and eject nitrogen frost over the surface. However, astronomers think that Triton may be a dwarf planet much like Pluto, captured from the Kuiper Belt. That makes it of massive interest to astronomers.
Are there any missions planned to visit Neptune?
Neptune has never been orbited; Voyager 2 was merely a brief flyby. However, a recent paper entitled Outer Solar System Exploration: A Compelling and Unified Dual Mission Decadal Strategy for Exploring Uranus, Neptune, Triton, Dwarf Planets, and Small KBOs and Centaurs recommends that a Neptune orbiter be given the highest priority. The paper’s authors put forward a plan to send a probe to orbit Neptune for between two and four years. In that time it would also conduct 10 flybys of Triton, and send a smaller probe into Neptune’s atmosphere.
Whether a mission to Neptune ever becomes a reality remains to be seen, but with the New Horizons’ flyby of Pluto providing such incredible and unexpected results, it could be that Neptune, Triton and the outer solar system in general will soon come into a much sharper focus.
Wishing you clear skies and wide eyes
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