dipper@utastro.UUCP (Debbie Byrd) (09/28/84)
Neptune is a giant planet -- but so far away we can't see it very well. More on how astronomers study this faraway world -- right after this. September 21 A Look at the Planet Neptune The Voyager spacecraft will encounter Uranus in 1986 -- and, if it continues to operate successfully, it'll give us our first close-up look at Neptune in 1989. Neptune is as wide as four planet Earths -- but so far away it's invisible to the naked eye. Even with a telescope, no features can be seen on the planet. For now, astronomers use sophisticated Earth-based technology to study the planet Neptune -- to learn such things as what it's made of -- and how fast it spins on its axis. Five years ago McDonald Observatory astronomers monitored subtle brightness changes of Neptune to discover its rate of spin. They showed that at least a major part of its atmosphere takes 18 hours, 44 minutes to go around. Since on the average the atmosphere and the main body of the planet have to go around at about the same rate, this figure -- three quarters as long as the Earth's day -- is probably close to the true rotation period of Neptune. A more recent study made from Chile used a new kind of electronic camera with a large telescope to obtain the first long series of good direct pictures of cloud features moving around Neptune. By tracking the clouds' movements these astronomers also estimated the rate at which the planet spins. This study came up with an estimate of 17 hours and 50 minutes for the rotation rate of Neptune. Once again, that's probably pretty close. Meanwhile, Neptune is awaiting its own visit from the Voyager spacecraft -- in the year 1989. Script by Deborah Byrd and Harlan Smith. (c) Copyright 1983, 1984 McDonald Observatory, University of Texas at Austin