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Mars at Opposition

March 3, 2012

Today, the layout of the solar system is well known. The Sun is in the middle, with eight planets at varying distances away from it. But it took a long time to develop that map. And one of the keys to making it work was a planet that’s putting in its best showing of the year right now: Mars.

The problem in understanding how the solar system is laid out is that we’re inside it. From that perspective, it’s easy to assume that we’re in the center of it -- which is what everyone thought about Earth’s place in the entire universe.

Over the centuries, though, astronomers worked it out by mapping the motions of the planets across the sky. They saw that Mercury and Venus never climb far from the Sun, so they deduced that those worlds are closer to the Sun than Earth is.

The other planets that are visible to the unaided eye pass all the way across the sky, sometimes lining up opposite the Sun, as Mars is doing right now. The bright orange dot rises around sunset, climbs high across the sky during the night, and sets around sunrise.

That alignment reveals that the planets orbit outside Earth’s orbit. And from the time it takes each world to loop through the background of stars, astronomers plotted each world’s relative position; those that took longer were farther away.

About five centuries ago, that work finally began to produce the first accurate map of the solar system -- with Mars one step outward from our own planet Earth.


Script by Damond Benningfield, Copyright 2012


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