Driftless Dark Skies

John Heasley

Driftless skywatchers could see a remarkable sight the morning of Feb. 18 when the waning crescent moon passes in front of Mars. Both worlds rise together in the southeast around 3:40. Mars will be just to the left of the sunlit side of the moon; binoculars will improve your view. As they rise higher in the sky, watch as they move closer together until 6:03 when Mars disappears as it is occulted by the moon. It may take up to 15 seconds for the moon to cover Mars. Mars stays hidden until 7:29 when it emerges from the dark side of the moon after sunrise. As you sip your coffee or tea, be sure to admire bright Jupiter and creamy Saturn to the left and below the moon as they rise in the southeast. All three planets will be gathering closer together as we head into March.
It’s a wonderful opportunity to ponder the scale of our solar system. While Mars is twice the diameter of the moon, it appears 1/350 the size because it is 700 times more distant. As we move through 2020, Earth and Mars draw closer together until October when Mars will be four times closer, quadruple the size, and 50 times brighter than this month. We can also consider the speed of the moon. It orbits around the Earth at over 2000 mph moving its own diameter every hour as viewed by us. So at first I thought Mars should be emerging after an hour and was perplexed why it would take longer. Then I realized, it takes more than an hour to see Mars again because it is speeding along at 54,000 mph and the moon needs the extra time to completely pass it. The next two mornings, the moon’s counterclockwise orbit (from right to left) brings it by Jupiter on the 19th and Saturn on the 20th. Continue to watch Mars and be sure to notice how it moves a little to the left every morning relative to the “fixed” stars in the background.
We’re watching worlds in motion in good company. On a spring evening 24 centuries ago (May 4, 357 BCE), Aristotle was the first recorded human to see the first quarter moon occult Mars: “For we have seen the Moon, half full, pass beneath the planet Mars, which vanished on its shadow side and came forth by the bright and shining part.” From this, he had evidence that Mars was more distant than the moon as humans slowly come to understand our solar system.
And if easy travel to other planets is your thing, head to the golden plains of Chryse Planitia on Mars where Viking 1 landed in 1976. Look homeward toward Earth after sunset on Feb. 18 and marvel as the waning gibbous moon transits across the waning gibbous Earth, briefly occulting the skywatchers of the Driftless.

John Heasley is an astronomy educator and stargazer who enjoys connecting people with the cosmos. He volunteers with NASA/JPL as a Solar System Ambassador and with the IAU as a Dark Skies Ambassador. For more information about stargazing in southwestern Wisconsin, like Driftless Stargazing LLC on Facebook and find out whenever there’s something awesome happening in the skies above.