The Sky This Week, 2012 July 24 - 31
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Rise of the Full Sturgeon Moon, 2008 Aug. 17 |
The Moon waxes in the evening sky this week, hugging the southern horizon as she passes through the summer Zodiac constellations. Full Moon occurs on August 1st at 11:27 pm Eastern Daylight Time. August’s Full Moon goes by many names and is variously known as the Grain Moon, Sturgeon Moon, Green Corn Moon, or the Lightning Moon. This will be the first Full Moon for August this year. The second will fall on the 31st. Luna starts the week in the company of Mars, Saturn, and the bright star Spica. Look for her just over five degrees below ruddy Mars on the evening of the 24th. On the 25th she forms a triangle with Saturn and Spica. On the 28th look for her gibbous orb five degrees northeast of the bright ruddy star Antares in the constellation Scorpius before drifting into the "Teapot" asterism of the constellation Sagittarius.
As the Moon brightens the evening sky the faint luminous swath of the Milky Way fades from view in even the darkest locations. This is a good time to familiarize yourself with some of the brighter stars and constellations of the summer sky.
Starting at the end of evening twilight, look to the west for a solitary rose-tinted star. Arcturus outshines everything west of the meridian by virtue of being the brightest star in the northern hemisphere sky. It is located about 37 light-years from us and has the highest proper motion of any first-magnitude star except the very nearby Alpha Centauri system. This rapid motion was discovered by English astronomer Edmond Halley in 1718.
Next, look toward the south where the ruddy star Antares lies on the meridian. Antares is a very evolved "red supergiant" star that leads a group of second-magnitude stars that trace out a fairly decent stick-figure scorpion. Most of these stars are young blue-giant stars that form a physical association, much the same way as the stars of Orion do. In mythology Scorpius and Orion were mortal enemies, so they were placed in opposite sides of the sky by the ancient storytellers. From our latitude the red star Betelgeuse in Orion sets when Antares rises, and vice-versa.
Look to the eastern half of the sky for the rising stars of the Summer Triangle. Highest and brightest of these is the blue-tinted star Vega, located just 25 light-years from the solar system. Vega is the lead star in the small constellation of Lyra, the Harp, a small parallelogram easily seen in binoculars. The southern tip of the Triangle is marked by Altair, another nearly star just under 17 light-years away. Altair leads the stars of Aquila the Eagle, a rather sparse group that gets lost in the Milky Way in the absence of moonlight. The eastern side of the Triangle features the star Deneb. Unlike its cohorts, Deneb is very far away, about 100 times the distance of Altair. In order to compete with its rivals it must therefore be intrinsically very bright, shining with the equivalent luminosity of over 100,000 Suns! Deneb marks the tail of Cygnus, the Swan, and the figure of the graceful bird can be seen extending into the Triangle’s center, where its head is the third-magnitude star Albireo. This star is one of the showpieces of the sky for the small telescope, an easily split double star of blue and golden yellow components. I like to call it "The Navy Star"!
Evening planets are now best observed as soon as the sky begins to darken. Mars and Saturn are now tightening their formation near the bright star Spica in the southwestern sky. Look for the Moon to visit them on the 24th and 25th. Mars is doing most of the chasing, closing the gap between Saturn and Spica by about half a degree per day. By the end of the week Mars will be just eight degrees west of Saturn, and during the second week of August he’ll pass between the ringed planet and the star. By that time we’ll know if the Mars Science Laboratory rover spacecraft will have had a successful landing. Even though his disc is now a tiny pink dot in the telescope eyepiece, if MSL succeeds we’ll be spending the summer looking at mars from a whole new perspective!
Saturn calmly awaits the arrival of Mars from his perch above the star Spica. He currently sets at around midnight, though, so try to catch a glimpse of him as soon as you can spot him. His rings are continuing to gradually open to our line of sight, now tipping over 18 degrees toward us.
Jupiter and Venus have been attracting quite a bit of attention from early morning commuters over the past few weeks. They will continue to do so, but they are gradually drifting apart. Jupiter will continue to rise earlier each day while Venus slows her pace relative to the Sun. Jupiter will stay in the vicinity of the bright star Aldebaran in Taurus for the next several weeks as Venus wends her way into the constellation of Gemini.
"The Sky This Week" will be taking a few weeks off during the month of August. If Internet access permits we’ll try to update a few times before returning to Washington. In the meantime enjoy the splendor of the summer sky wherever you happen to be, and as the late Jack Horkheimer used to say, "Keep looking up!"
