The Moon Gets Company

This past Monday, Aug. 13, the moon was new.  If you were to imagine a 93-million-mile line connecting Earth to the sun, then the moon was on that line — in between the other two.  Any sunlight that hit the moon, therefore, bounced right back to the sun and never made its way to our planet.  So, since the moon does not produce its own light, it was not visible to us.

   Now the moon continues its monthly sweep away from the sunny side to the outer or “night†side of Earth. As it gets closer and closer to the night side of Earth, more and more of the sun’s rays can both reach the moon and reflect toward us.  An increasingly greater portion of the moon’s disc is visible and the moon appears to “wax.â€

   This week, the moon will wax from a slim crescent to a hearty “gibbous†(three-quarter).  If you look to the low west shortly after sunset (at about 7:53 p.m.), the night of Friday, Aug. 17, you’ll find that the crescent has some company.  Directly to the left of the moon and toward its top will be a singularly vivid star: the most obvious object in the moon’s neighborhood.  

   This star is Spica.  

   Spica is the brightest star in the zodiac constellation Virgo.  It is the 15th brightest of all stars visible from anywhere, anytime, on Earth. Spica is approximately one-and-a-half times as massive as our sun.  It lives approximately one-and-a-half quadrillion miles away from us. This means that for Spica’s light to reach your eye, it has traveled for approximately 260 years. The Spica you see is actually the Spica that existed before the American Revolution.

   What of the Spica that exists now? We have no way of knowing if there even is one.

   We nonetheless expect Spica to remain home in Virgo each night after Aug. 17.  But the moon will continue to slide to the left — farther and farther away from the constellation.  Spica will thus become more difficult to identify.  

   Half of the moon will be illuminated Monday, Aug. 20.  One would expect the moon to appear full roughly a week later — on Tuesday, Aug. 28.  This month, however, things will be delightfully different.  Nature has lined things up for the totality of the moon to be eclipsed by Earth’s shadow!

  Stay tuned.

   Readers with astronomy questions are invited to send them to Compass@lakevillejournal.com for an answer or explanation from Dan Yaverbaum.