July offers an array of action in the night skies from several stars and planets that are clearly visible despite the brightening moon that culminates in Sunday’s full moon.
Jimmy Westlake's Celestial News column appears Tuesdays in the Steamboat Today.
Find more columns by Westlake here.
The second full moon of the summer season traditionally is called the Green Corn Moon and happens this year Sunday. As we get closer to this date, the brightening moon has the effect of dimming starlight, rendering all but the brightest stellar objects invisible. Fortunately for us, there are plenty of bright stars and planets this month that will shine right through the moonlight.
For example, even under the light of a full moon, the three bright stars of the Summer Triangle still will dominate the eastern sky in the early evening. Vega, Deneb and Altair are our constant summer companions.
High overhead is the brightest star visible on summer nights, the orange-giant star Arcturus. Just follow the arc of the Big Dipper’s handle to find Arcturus. Extending that same arc a bit past Arcturus will lead you to another of summer’s celestial gems, Spica, while the red supergiant star Antares twinkles prominently in the southern sky.
Rounding out the top seven brightest stars of summer is Regulus, the star marking the heart of Leo the Lion. Regulus is mixing it up with several bright planets in the western sky this month, right after sunset. The brightest and most obvious of these is Venus, the lovely “Evening Star,” with Mars and Saturn shining to Venus’ upper left and Mercury peeking out of the sunset glow to Venus’ lower right. Regulus will be tough to spot in the evening twilight, on a line between Venus and Mercury, but watch on the evenings of July 26 and 27, when Mercury and Regulus will twinkle side by side, less than one degree apart. Mercury will be the brighter of the two.
Mars has close encounters of its own Saturday and Sunday evenings, when it will make a close pass by the star Zavijava in Virgo. Mars, the brighter, will pass less than one-fourth of a degree from Zavijava, whose name means “the Dog Kennel.” Then, watch closely, night by night, as Mars creeps up on Saturn and passes it July 30. Saturn, the brighter, will shine only two degrees above Mars on that date. The planets’ proximity is just an illusion, though, since Saturn will be 10 AUs from Earth while Mars is only 2 AUs away. One AU, or astronomical unit, is the average distance between Earth and the sun, about 93 million miles.
The climax of this planetary dance happens early next month, when you’ll be able to hide three planets — Venus, Mars and Saturn — behind your thumb all at once.
Professor Jimmy Westlake teaches astronomy and physics at Colorado Mountain College’s Alpine Campus. He is an avid astronomer whose photographs and articles have been published all across the world. His “Celestial News” column appears weekly in the Steamboat Today newspaper and his “Cosmic Moment” radio spots can be heard on local radio station KFMU. Also, check out Jimmy’s astrophotography website at www.jwestlake.com.