Image Courtesy of NASA/JPL-Cal Tech
Observing Neptune
Neptune is the furthest planet from the Sun and is agreeably the most difficult to observe due to its distance. It is impossible to see with the naked eye as its apparent brightness is simply too dim. Neptune can be seen as a point of light through binoculars and most small telescopes. A high powered telescope will show its shape and color as well its moon Triton. Like Uranus, it is made up mostly of hydrogen and helium, with some ammonia and methane as well. (The methane is responsible for giving the planets their blue color.)
Finding Neptune
Because Neptune cannot be seen with the naked eye, it is very difficult to find on its own, although its slow moving 165 year orbit makes its position very predictable. The best time to observe Neptune is at opposition although in reality it makes little difference because it is so distant. The dates of the opposition of Neptune are listed on the Astronomical Calendar.
Facts about Neptune
Average Distance from the Sun: 30.06 AU (4,497,000,000 km)
Orbital Period: 164.8 years
Length of Day: 16.1 hours
Mass: 1.03x1026kg (17.14 earth masses)
Diameter (equatorial): 49,528 km (3.88 times the earth)
Average Surface Temperature: -216°C / -357°F
