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Why is Mars near the moon on eclipse night?

Posted by
Deborah Byrd
and
April 14, 2014

On the night of April 14-15, the night of the first of four total lunar eclipses in the coming tetrad, you’ll find a very bright red “star” near the moon. It’s really not a star at all, but the red planet Mars. Why is Mars near the moon on the night of the lunar eclipse? The answer is simple. On April 8, Earth in its smaller orbit passed generally between Mars and the sun. Our motion in orbit has placed Mars opposite the sun from our point of view, visible all night while the sun is below our feet. It’s what astronomers call an opposition of Mars. Meanwhile, a full moon is also, always, opposite the sun. It must be so, in order to appear full from Earth. An outer planet is always near the full moon during the month it reaches opposition. A total eclipse always happens at full moon. Voila! Mars is near the moon on eclipse night. Hopefully, the illustrations below will help you visualize it. Clear skies, everyone!

Read more: Total lunar eclipse for the Americas April 14-15

Read more: Mars is also closest in six years on eclipse night

In order to appear full from Earth, the moon must be opposite Earth from the sun, and its fully lighted hemisphere must be facing our way. Likewise, for a lunar eclipse to occur, the moon must be full - opposite the sun. Illustration via Matt Daniel with CNN Weather. Used with permission.
In order to appear full from Earth, the moon must be opposite Earth from the sun, and its fully lighted hemisphere must be facing our way. Likewise, for a lunar eclipse to occur, the moon must be full – opposite the sun. Illustration via Matt Daniel with CNN Weather. Used with permission.
Mars is also opposite the sun during during April, 2014. This NASA illustration shows Earth and Mars in their orbits, which are slightly inclined to each other's. That's why Earth doesn't pass in front of the sun each time it sweeps between the sun and Mars, as it did last on April 8. Moon opposite the sun on April 14-15. Mars generally opposite the sun throughout April 2014. Thus Mars is near the moon on eclipse night.
Mars is also opposite the sun during during April, 2014. This illustration shows Earth and Mars in their orbits, which are slightly inclined to each other. Earth swept generally between Mars and the sun on April 8. Moon is opposite the sun on April 14-15; it must be in order to appear full and in order for an eclipse to occur. Thus Mars is near the moon on eclipse night. NASA illustration via honolulu.hawaii.edu.
On the night of April 14-15, the planet Mars - closest in 6 years - will be near the eclipsed moon. The star Spica will also be nearby. Illustration via Classical Astronomy.
On the night of April 14-15, the planet Mars – closest in 6 years – will be near the eclipsed moon. The star Spica will also be nearby. Illustration via Jay Ryan Classical Astronomy.

Bottom line: The red planet Mars is near the moon on eclipse night, April 14-15, 2014. This post explains why.

Posted 
April 14, 2014
 in 
Human World

Deborah Byrd

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About the Author:
Deborah Byrd created the EarthSky radio series in 1991 and founded EarthSky.org in 1994. Prior to that, she had worked for the University of Texas McDonald Observatory since 1976, and created and produced their Star Date radio series. Today, she serves as Editor-in-Chief of this website. She has won a galaxy of awards from the broadcasting and science communities, including having an asteroid named 3505 Byrd in her honor. In 2020, she won the Education Prize from the American Astronomical Society, the largest organization of professional astronomers in North America. A science communicator and educator since 1976, Byrd believes in science as a force for good in the world and a vital tool for the 21st century. "Being an EarthSky editor is like hosting a big global party for cool nature-lovers," she says.

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