Moon and Spica on July 8 and 9

On July 8 and 9, 2019 – 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 special star. The bright star to the east of the moon on July 8 is none other than Spica, the sole 1st-magnitude star in the constellation Virgo the Maiden.

The much brighter starlike object to the east of Spica (outside the sky chart at the top of this post) is the giant planet Jupiter. Jupiter, the fifth planet outward from the sun, shines rather close to Antares, the brightest star in the constellation Scorpius the Scorpion. Looking ahead, the moon will sweep by Jupiter (and Antares) from July 12 to 14.

The sky chart at the top of this post is set for North America. If you live in the Earth’s Eastern Hemisphere, the moon will appear a little farther west of Spica. If you live in Hawaii, the moon will be offset somewhat in the direction of Jupiter. Also, the moon on the sky chart appears larger than it does in the real sky.

Star chart of just past full moon, Jupiter and Antares at nightfall.

During the next several days, watch for the waxing gibbous moon move away from Spica and toward the star Antares and the king planet Jupiter. The moon will sweep by Antares and Jupiter on July 12, 13 and 14, 2019. Read more.

No matter where you live, the moon continually moves eastward in front of the backdrop stars of the zodiac at the rate of about one-half degree per hour. For a convenient measuring stick, the moon’s angular diameter approximates one-half degree of sky. So the moon moves its own diameter eastward per hour or about 13 degrees (26 moon diameters) eastward per day. Look for the moon to snuggle up more closely with Spica as darkness falls on July 9.

When the moon is no longer close to Spica, you might find it helpful to “star-hop” to Spica instead, as shown on the sky chart below:

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Star chart showing Big Dipper with line to Arcturus continuing to Spica.

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 8 and 9, 2019, and then use the Big Dipper to locate Virgo’s brightest star, after the moon’s flirtation with Spica ends.

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Bruce McClure