dipper@utastro.UUCP (Debbie Byrd) (07/17/85)
Today the planet Mars is traveling behind the sun from Earth. More on Mars at conjunction -- after this. July 17 Mars Behind the Sun During the night on Wednesday, the planet Mars is at conjunction with the sun. That's an Earth-centered way of saying that Mars is now traveling behind the sun from Earth. Conjunction is a word used when talking about the sky in an imaginary way -- as though Earth is in the middle of everything -- and the sky is a sphere surrounding Earth. Mars at conjunction with the sun means that Mars and the sun today have the same right ascension -- that's like celestial longitude -- on the imaginary celestial sphere surrounding Earth. If the sky really were the inside of a globe surrounding Earth, then today Mars and the sun would be right next to each other -- they'd have the same longitude on this imaginary sphere. But the sky isn't a sphere around Earth. What's really happening is that today Mars is beyond the sun from Earth in the solar system -- traveling along directly opposite where we are. We can't see Mars now -- and won't until summer is over -- because the red planet is now hidden in the sun's glare. Mars is now moving toward the outermost part of its orbit around the sun -- its aphelion -- in mid-October. So though it's traveling beyond the sun from Earth today, it's not as far from us as it will be later this month. Today Mars is just under 22 light-minutes away -- on July 30 it'll be farthest from us, slightly more than 22 light-minutes away. Script by Deborah Byrd. (c) Copyright 1984, 1985 McDonald Observatory, University of Texas at Austin