Why is Mars sometimes bright and sometimes faint?
Mars is so faint it is hard to see. Last year it was very bright. What causes this?
Mars is the world orbiting the sun one step outward from Earth’s orbit. Earth takes one year to orbit the sun once. Mars takes two years.
The brightness of Mars in our sky depends on where our two planets are in orbit around the sun. Sometimes Earth is close to Mars, and sometimes we are far away. We are close – and Mars appears very bright in our sky – around the time Earth passes between the sun and Mars. This happens about every two years.
So alternates in appearing bright and faint in our sky. It’s bright in the years we pass between Mars and the sun. It’s faint in the years in between.
Earth passed between the sun and Mars in late August 2003. Then Mars was just over three light-minutes from Earth. So Mars was very close to us then, and it appeared as a blazing reddish “star” in our night sky, rising in the east while the sun was setting in the west. Mars was also close in 2005, and it will be again in 2007. And so it will be close and bright every two years for billions of years to come!
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