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SYFY WIRE Bad Astronomy

Venus, Mars, and the Moon Go to Sleep

By Phil Plait

A couple of weeks ago, the interplay of the inexorable dance of gravity and the perspective brought by geometry combined to bring three celestial objects together: Venus, Mars, and the Moon. They all appeared very close together, in an event technically called an appulse, but what most people more casually call a conjunction.

Unfortunately it was cloudy and/or snowing here in Colorado, so I couldn’t see it for myself, but people from all over the world took pictures and posted them to Twitter and Facebook. That was nice; if I couldn’t see it for myself, at least I could see it through the eyes and lenses of others.

Astrophotographer Jeff Sullivan (who has contributed many amazing photos and videos to this blog) realized he could get dramatic footage of them setting behind Mount Whitney in Northern California if he went to Lone Pine. Oh, he was very right. This animation is short, but oh so lovely:

Venus is the brighter of the two “stars” to the lower left, with Mars just above it. Venus orbits the Sun closer than Earth, and is currently about as far from the Sun as it can be in our sky. It’s swinging around its orbit and headed to get between us and the Sun in August.

Mars, on the other hand, orbits farther out, and was on the far side of its orbit. During this encounter Venus was about 210 million kilometers from Earth, and Mars was closer to 330 million. The Moon was a mere 359,000 km away (measured from the centers of the Moon and Earth). It was very nearly between us and the Sun, making it a thin crescent. Note the Earthshine, the "dark" side of the Moon softly illuminated by light from the Earth itself.

The night before this happened wasn’t as cloudy here, and I could see Mars and Venus just a degree or so apart over the Rockies. As they slowly sank to the west after sunset, I could visualize their orbits in the sky, projecting their motions in my mind’s eye as the enormous virtual gears of the Universe turned and interlocked.

That to me is one of the most profound and wonderful things about viewing the sky: The utter inevitability of the motions of celestial objects; knowing that, with keen enough observations and a grasp of the math, this event could have been predicted millennia ago, and would have occurred right on time.

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