Sky Talk June 2010: Mars & Venus on the Move!

Even casual skywatchers are aware that planets slowly wander about the sky, being visible at differing times during the night and throughout the year. But occasionally they pass very close to bright stars, and at such times their orbital motion becomes strikingly obvious over a period of just days and even hours! Or they may simply change the patterns they form with two or more surrounding stars. This month offers a superb opportunity to see examples of both for yourself.

As June opens, the ruddy-orange planet Mars is located near the bright blue-white star Regulus in Leo the Lion, positioned high above the western horizon after darkness falls. (Set your Scientifics Star and Planet Locator for around 10:00 p.m. local time to identify the constellation.) Both objects lie within the same wide binocular field of view, with Mars pulling closer and closer to Regulus each evening. On the nights of June 5th and June 6th, the star and planet will finally lie less than one degree apart — close enough to look like a lovely contrasting double star in 7x and 10x glasses. And better yet, both objects will easily fit within the same low-power eyepiece view of telescopes like the Scientifics 60mm refractor, the 76mm Celestron FirstScope, and the 105mm Edmund Astroscan Plus. Switching to their higher power eyepieces and lingering for an hour or so (or coming back to them after a break), you’ll see that the gap between star and planet has changed due to Mars’ orbital motion. Following this close approach to each other (technically called a planetary “conjunction”), Mars then moves rapidly eastward away from Regulus the remainder of June.

Another example of planetary motion this month is provided by radiant Venus and its changing configuration with the stars Castor and Pollux in Gemini the Twins, positioned above the west-northwestern horizon after dusk. (Again, use the Star and Planet Locator to identify the constellation.) On June 11th, the three objects will form a perfectly straight line, with Venus lying east of the stars themselves. But only two or three nights later, that pattern will have obviously changed, with the planet lying north and east of Castor and Pollux. Imagine how mystified the ancient skywatchers were at these antics, knowing nothing of the true physical nature of neither planets nor stars. To them, the planets were simply gods — and restless ones at that!

On the evenings of June 13th and June 14th, a slender crescent Moon will add to the overall beauty of the scene. It, too, will continue to move eastward and higher in the sky each night as the month progresses. Truly the heavens are alive with movement and change for those who will take time to look up at the celestial pageantry being played out over their heads every clear night of the year. Don’t miss it!

–James Mullaney
Former assistant editor at Sky & Telescope magazine and author of seven books on stargazing.

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