Re: why was Mars so much closer this year than any other year since 5000 b.c.

Dear Jack,

It’s curious that no one has asked that question that I’ve heard. The reason Mars is sometimes closer or further from us is this. Both Mars and Earth orbit the sun in ellipses. Currently Earth is further from the sun - aphelion - 149,597,871 kilometers - in July and closest to the sun, parhelion - 147,092,106 kilometers in January. So in the summer we are about 2.5 million km closer to the orbit of Mars.

Mars has an even more elliptical orbit. At parhelion, 30 Aug 2003, Mars was only 206,679,931 km from the sun. When it reaches aphelion on 7 Aug 2004 it will be 249,207,613 km from the sun, about 43 million miles further away.

Earth orbits the sun in about 365.25 days. Mars’ year is about 687 days long, more than twice ours. So every two years and a few weeks, we pass Mars. It is our good fortune to be living right now when the orbital periods of our two planets bring our aphelion at almost the same time as Mars’ parhelion. That won’t happen again for a very long time: The next best opposition of the Red Planet is fifteen years from now in 2018 when Mars will appear 24.3 arc seconds in diameter. On 28 Aug 2003 it appeared 25.1 arc seconds in diameter.

Surf to the website of the Grand Rapids Amateur Astronomical Association at http://www.graaa.org and click on Links to find planetarium software which you can download to explore Mars' oppositions. NASA has an online Solar System Simulator at http://space.jpl.nasa.gov/.
Thanks for asking!

Jim Foerch
Veen Observatory
Lowell, Michigan
USA