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Treebeard's Stumper Answer
19 April 2002

Line Dance of the Planets

Over the next few weeks, we can witness a rare and beautiful dance of the planets. All five visible planets will be in the sky at once -- Jupiter, Saturn, Mars, Venus, and Mercury. Look west after sunset, and keep looking night after night because the planets will change positions in an intricate line dance. These five planets were named in ancient times, but how did those ancient astronomers realize that planets are different from the other stars? It's unusual that all these planets are in the sky at once, but it's not surprising that they are all in a line. Why?

These handsome horizon charts illustrate some of the moves in this line dance of the planets. They are from Alan M. MacRobert's article on A Rare Dance of Planets at the Sky And Telescope web site. Click on any image to go to the original which gives a detailed week by week description.
Star charts adapted from Alan M. MacRobert's A Rare Dance of Planets at Sky And Telescope.
You can create your own custom maps using the nifty Sky And Telescope Interactive Sky Chart.
Note the different motions in this line dance. Jupiter and Saturn are moving down from the upper left. Brilliant Venus is rising at the same time, and finally overtakes Jupiter on June 3. Mercury rises and sinks. Mars and Saturn swap positions, and then they both sink. It's not quite an "allignment," though all five visible planets (plus the crescent Moon) will be clustered within 33 in sky on the evening of May 14th.

Here are a few more related planetary stumpers:

Our word "planet" comes from the ancient Greek word for a wanderer. Everything in the sky revolves by day and year, but the stars keep their positions with each other. The ancients noticed that the planets (they included the sun and moon) wander across the background stars. It's not surprising that all the visible planets are arranged in a line, because the solar system is flat. Planets can be anywhere in their orbits, but we see them in the flat plane of the solar system, along the slice of the sky called the ecliptic and the constellations of the zodiac.


I fell behind on my stumpers this week because of my Dunn Middle School Science Fair. (My project was about Secret Santa.) Actually I stole one of my own (ancient) stumpers about Pretty Planets all in a Row (05 Dec 97). The real stumper for me has been finding time to get outside to see all these planets. I live in a canyon with no view to the west, and I spend more time staring at my computer than the sky. Graybear came through with all the right answers!

Thanks Graybear, that really did help.

For more information about who's who in this spring dance of the planets, check Sky & Telescope, NASA, and Abrams Planetarium (PDF). You can download fine star charts from The universe awaits if you Search the Web.

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