Tonight – July 12, 2016 – as the setting sun closes the curtains on the day, and the darkening skies bring out a myriad of far-off suns, let the moon introduce you to a very special star. The nearby bright star to tonight’s moon is none other than Spica, brightest light in the constellation Virgo the Maiden.
Did you see the moon and Spica yesterday, on the evening of July 11? Note the moon’s change of position relative to Spica as darkness falls tonight, on July 12. The moon continually moves eastward in front of the backdrop stars of the Zodiac at the rate of about one-half degree per hour or about 13o per day. For a convenient measuring stick, the moon’s diameter approximates one-half degree of sky, and your fist at an arm’s length about 10o on the sky’s dome.
In a few to several more days, in fact, the moon will be farther from Spica on the sky’s dome, and closer to the planets Mars and Saturn. When that happens, you might find it helpful to “star-hop” to Spica instead, as shown on the sky chart below.
If you live in the Northern Hemisphere, and you’re familiar with the Big Dipper, you can count on this famous pattern of stars to guide you to Spica. Simply extend the Big Dipper handle to arc to the brilliant yellow-orange star Arcturus and then to spike Spica, a blue-white gem of a star. (If you have difficulty discerning stellar color with the eye alone, try your luck with binoculars.)
Bottom line: Let the moon guide you to Spica on July 12, 2016, and then use the Big Dipper to locate Virgo’s brightest star, after the moon’s flirtation with Spica ends.