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It's summer — here comes the Mars e-mail!

posted Wednesday August 12, 2009

Every summer since 2003, an e-mail has been "spammed" around the world that claims Mars will be as large as the full Moon in the August night sky.

That's not true! If you receive that e-mail, delete it. Tell your friends to delete it. Here's the truth:

Mars will never look as large as the Moon in our sky. Even at its closest distance, Mars is more than 35 million miles away from Earth. The Moon is much closer to Earth than Mars is — the Moon is about 250,000 miles away from our planet.

Remember: Mars is locked in its orbit around the Sun. It will never come close enough to Earth to look like more than just a bright star in the sky.

Why did this e-mail begin?

In August 2003, Earth and Mars passed closer than they had in 60 thousand years. Mars looked like a very bright star to the naked eye. If you had looked at Mars through a telescope at that time, Mars would have looked as large in the telescope as the full Moon looks to the naked eye.

Our view of Mars changes regularly as both Earth and Mars orbit the Sun. Because Earth is closer to the Sun, it can complete its orbit faster than Mars can.

As a result, every two years and two months, Earth "laps" Mars in its orbit and the two planets align on the same side of the Sun. At these times, Earth and Mars are at their closest distance. Even at these times, if you look into the night sky without a telescope, you will see Mars as a bright star-like (but not twinkling) object.

The Mars e-mail "spam" has been documented on many Web sites. Here are two that you may want to visit for more information (both are from the 2006 "Mars e-mail" season, but the information is still valid):

Sky & Telescope magazine
Snopes: the Internet authority on e-mail hoaxes and urban legends