Venus and Mars put on a predawn show this week

The pair is especially worth looking for this week, as the planets appear to pass each other from our vantage point here on Earth.

Posted 2:18 p.m. Oct 2, 2017 — Updated 2:18 p.m. Oct 2, 2017

Tony Rice

RALEIGH, N.C. — October begins with Venus and Mars in the predawn sky, so look low on the eastern horizon about an hour before sunrise. The pair is especially worth looking for this week, as the planets appear to pass each other from our vantage point here on Earth.

Venus will be lower on the horizon each morning this week, while Mars will be a bit higher. The two will appear less than one-quarter of a degree apart the morning of Oct. 5.

On Thursday, brightly shining Venus may make it difficult to make out dimmer, redder Mars. While the dance between these planets is interesting to see, there’s a demonstration of how the solar system works going on right in front of our own bleary eyes. Mars will be higher in the sky each morning, but not by much, and Venus will be much lower than Mars. This is due to their orbits.

Mars appears to move more slowly through our sky because its year is three times that of Venus'. With Venus traveling at over 78,000 mph and Mars at nearly 54,000 mph in their orbits, this appearance that they are moving in opposite directions doesn't’t make sense at first glance.

This is a matter of perspective. This effect can also be seen on the road as you pass a slower moving vehicle. Focus on that other vehicle and, though it's moving just a few mph slower than yours, the slower vehicle appears to be moving backward. The illusion is broken as soon as you look to the background just a few feet away.

Your eye is more easily fooled against the background of stars in the night sky, however. The forward motion around the sun remains much more hidden as Venus and Mars dance around Sigma Leonis, a blue-white star in the constellation Leo 210 light years away.

Tony Rice is a volunteer in the NASA/JPL Solar System Ambassador program and a software engineer at Cisco Systems. You can follow him on Twitter @rtphokie.

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