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Mars, Saturn, and Spica

August 8, 2012

A bright triangle adorns the western sky the next few evenings. It’s fairly low in the west-southwest as night begins to fall, and slides to the lower right over the following couple of hours.

The top point of the triangle is the planet Saturn, with the star Spica to its lower left and the planet Mars to its lower right. Saturn is the brightest of the three, although not by a whole lot.

The configuration will change from night to night as Saturn and particularly Mars move against the background of true stars. That’s because the planets are much closer to Earth than the stars are. As these worlds orbit the Sun, they loop all the way through the starry background. Mars is less than one-fifth as far as Saturn is right now, so it moves a greater distance across the sky from night to night — the result of the combined orbital motions of Earth and Mars itself.

The three objects will remain close together for a while, but their configuration will change. Mars will pass between Saturn and Spica early next week, so for a couple of nights the triangle will become a more-or-less straight line. And after that, Mars will move to the left of the other two, forming an ever-widening triangle.

Spica and Saturn are dropping closer to the Sun as seen from Earth, so they’ll disappear in the twilight by late next month. But Mars won’t be done for quite a while. It will remain in view until early next year.

Tomorrow: One big happy family.

Script by Damond Benningfield, Copyright 2012


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