Neptune & Pluto


Neptune & Pluto Facts
Neptune is a gaseous planet made of hydrogen and helium. It is very like Uranus but is largely blue in colour due to the composition of its atmosphere. Neptune average distance from the Sun is 4,495 kilometres and its orbit sometimes extends beyond the orbit of Pluto, and from 1979 to 1999 Neptune was farther from Sun than Pluto. Neptune has two large moons, Triton and Nereid. Triton, one of the largest moons in the Solar System, is unusual because it moves in a circular orbit from east to west.

Pluto may well have been a moon of Neptune at one time. It is the most distant planet from the Sun and takes 248 years to orbit the Sun and won't return to the position it was discovered in until 2177. It was discovered in 1930 by an American astronomer, Clyder Tombaugh, when he compared photographic plates of the night sky and saw that a 'star' had moved. Temperatures on Pluto, are extremely low, ranging from about -230 to -200 degrees Celsius. Pluto's only moon, Charon, was discovered in 1978. It is almost the size as Pluto (with a diameter of 2,285 kilometres), and the Pluto-Charon system is rather like a double planet. Charon circles Pluto every 6.3 days. Because Pluto rotates every 6.3 days, Charon appears to be stationary in the sky, like a geostationary satellite orbiting the Earth.

The double planet, Pluto and its moon, Charon

Neptune & Pluto Surface
Neptune has a very active atmosphere with high-speed winds that swirl around the planet faster than it rotates. The winds carry 'scooter clouds' around the planet at speeds of 2,400 kilometres per hour. Pluto surface probably consists of frozen water, ammonia and methane.


Observing Neptune & Pluto
Under most circumstances, the disc of Neptune is invisible with apertures of 8 inches or less. Powers of x200 or more are needed to show the disc. Under good seeing conditions it definitely has a non-stellar appearance with apertures over about 9 inches used with sufficient magnification (about x500). A magnification of x800 makes Neptune look the same size as the full Moon to the naked eye but it is much dimmer, of course. The disc will look featureless, in fact very few, if any, features have ever been certainly recorded on Neptune's disc by Earth-based telescopic observation.

Pluto is too faint to be visible to the unaided eye, attaining a maximum brightness of magnitude 13.7 at its closest approach to Earth. Finding and identifying Pluto is an observing challenge. It is visible in telescopes of 8 inches of aperture or more and may be visible in a 6-inch telescope under dark skies. It appears as a faint star-like point of light and can be photographed with a 200-mm lens. The Observer's Handbooks published annually by the Royal Astronomical Society of Canada and others, give charts showing the position of Pluto against the background of fixed stars around the date of opposition each year. Detailed instructions for locating Pluto are given by fixing on a nearby prominent star and then by a stepwise 'star hopping' sequence the observer is enabled to find Pluto. Its movement relative to the other faint stars must be detected by making accurate drawing of the stars in the vicinity of the object suspect of being Pluto and observing the same star field again next night. If the suspected object has moved then it was Pluto. Needless to say, a dark moonless night with steady seeing is very desirable when you go Pluto hunting.

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