dipper@utastro.UUCP (Debbie Byrd) (06/25/85)
It may now be possible to see the planet Mercury in the evening sky. More -- after this. June 25 Mercury, Castor and Pollux The shy planet Mercury has been lost in the sun's glare all this month. But beginning around now -- and getting better for the next few weeks -- you may be able to see Mercury in the evening. If you can see it, it'll be low in the west after sunset -- shining like a star -- shortly after the sun goes down. There are two stars now near Mercury on the dome of the sky. They are Castor and Pollux, the starry eyes of the twin boys in the constellation Gemini. Mercury is five degrees south of Pollux Tuesday evening on the imaginary celestial sphere surrounding Earth. In the western twilight sky, the planet appears brighter and slightly below the two stars. Mercury looks like the stars in our sky. But stars are great shining balls of gas -- very far away. And Mercury is a relatively little round rock -- about three thousand miles in diameter -- moving around our local star, the sun. Mercury is smaller than most other worlds in the solar system -- and smaller than two of the solar system's moons -- Titan and Ganymede. This little world -- innermost to the sun -- is an interesting place. A spacecraft called Mariner 10 sped past the planet three times in the mid-1970s. Among other unexpected discoveries, it found a fully developed magnetic field for Mercury -- similar to the magnetic field of Earth -- which causes compasses on our world to point north. A magnetic field is evidence for dynamic processes taking place in Mercury's interior -- which still aren't fully understood. Script by Deborah Byrd. (c) Copyright 1984, 1985 McDonald Observatory, University of Texas at Austin