As night descends on July 4, 2014, look in the southwest for the moon near the planet Mars. This planet, still in front of the constellation Virgo, is not as bright as it was in April 2014, when Earth passed between Mars and the sun. But it’s still wonderful to behold. The star near it is Spica, Virgo’s brightest star. The moon will be closer to Mars on July 5. In fact, from parts of Earth tomorrow, the moon will cover Mars in an event called an occultation by astronomers. So find Mars tonight! Then enjoy the moon closer tomorrow.
And here’s something else you can enjoy on this July evening, especially if you have a dark sky. It’s the constellation Corona Borealis, also known as the Northern Crown. To see this famous C-shaped assemblage of stars during the evening hours in July, you will be looking high overhead. The constellation is distinctive. It looks like a half-circle, in the middle of which is a white jewel of a star called Alphecca or Gemma.
The Crown is located more or less along a line between two bright stars: Arcturus in the constellation Bootes the Herdsman and Vega in the constellation Lyra the Harp. Arcturus has already passed its highest point in the evening at this time of year and is slowly descending to the west. Vega is still high in the east on July evenings. With dark skies you will notice the orange color of Arcturus, and Vega’s bright blue-white tinge. Corona Borealis can be found between these two stars, but you will need a dark sky to see the faint semi-circle of stars composing this constellation.
The meaning of the Latin star name Gemma should be obvious. This star is the gem of the Northern Crown. But the star is also called Alphecca, from an Arabic phrase meaning the bright one of the dish. Gemma, aka Alphecca, is an eclipsing binary system. It consists of a smaller sun-like star that passes in front of a brighter star every 17.4 days, as seen from our earthly vantage point.
Bottom line: On these sultry July evenings, look for Corona Borealis’ graceful semi-circle of stars to crown the top of the sky as soon as darkness falls, in between summertime’s two brightest stars: Arcturus and Vega. On July 4, 2014, look for the moon and Mars in the southwest when night falls. The moon will be even closer to Mars on July 5.