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The Night Sky of July

Dr. Wayne Wooten
Professor of Astronomy

For July 2017, the Moon will be first quarter on July 1st. The waxing gibbous moon passes three degrees north of Saturn in the SE evening sky on July 6th. The Full moon, the Thunder Moon, is on July 9th. The Moon is last quarter on July 16th. The waning crescent moon passes three degrees south of Venus in the dawn on July 20th. The new moon is July 23rd, and of course, the very next new moon is the solar eclipse of August 21st! The waxing crescent moon is just below Mercury on July 24th, and then passes three degrees north of Jupiter on July 28th, and the moon ends the month as it started, with a first quarter phase on July 30th.

Mercury comes into the evening sky as July begins, but with stay low in the west. The most photogenic shot will when the crescent moon, Mercury, and the bright star Regulus (which will be in the Sunís Corona on August 21st!) are grouped together on the evenings of July 24-25th; look with a clear western horizon about 30-40 minutes after sunset to catch this beautiful trio.

Venus dominates the dawn sky, passing among the stars of Taurus at midmonth. On July 14th, she passes 3 degrees north of the bright orange star Aldeberan. Mars lies hidden in the sunís glare for now, but a year from now will be at opposition, the best time to see it since August 2003. Jupiter is still well up in the west at sunset, about five degrees east of Spica in Virgo. It will be lost in the sunís glare by September, so enjoy its moons, belts and zones, and Great Red Spot while you can. Saturn is also well placed for evening observing in July, just above the tail of Scorpius in the SE. It is tilted 27 degrees toward us and the Sun, and the rings and moons are the most beautiful sight in the telescopic sky. Our feature photo shows the rings tilted sunward currently.

Overhead, the Big Dipper rides high at sunset, but falls lower in NW each evening. Good scouts know to take its leading pointers north to Polaris, the famed Pole Star. For us, it sits 30 degrees (our latitude) high in the north, while the rotating earth beneath makes all the other celestial bodies spin around it from east to west.

If you drop south from the bowl of the Big Dipper, Leo the Lion is in the SW. Note the Egyptian Sphinx is based on the shape of this Lion in the sky. Taking the arc in the Dipperís handle, we "arc" SE to bright orange Arcturus, the brightest star of Spring. Cooler than our yellow Sun, and much poorer in heavy elements, some believe its strange motion reveals it to be an invading star from another smaller galaxy, now colliding with the Milky Way in Sagittarius in the summer sky. Moving almost perpendicular to the plane of our Milky Way, Arcturus was the first star in the sky where its proper motion across the historic sky was noted, by Edmund Halley.

Spike south to Spica, the hot blue star in Virgo, then curve to Corvus the Crow, a four sided grouping. Jupiter lies just east of Spica this July . North of Corvus, in the arms of Virgo, is where our large scopes will show members of the Virgo Supercluster, a swarm of over a thousand galaxies about 50 million light years distant.

To the east, Hercules is well up, with the nice globular cluster M-13 marked on your sky map and visible in binocs. The brightest star of the northern hemisphere, Vega (from Carl Saganís novel and movie, "Contact"), rises in the NE as twilight deepens. Twice as hot as our Sun, it appears blue-white, like most bright stars. At the opposite end of the parallelogram of Lyra is M-57, the Ring Nebula.

Northeast of Lyra is Cygnus, the Swan, flying down the Milky Way. Its bright star Deneb, at the top of the "northern cross" is one of the luminaries of the Galaxy, about 50,000 times more luminous than our Sun and around 3,000 light years distant. Under dark skies, note the "Great Rift", a dark nebula in front of our solar system as we revolve around the core of the Milky Way in the Galactic Year of 250 million of our own years.

To the east, Altair is the third bright star of the summer triangle. It lays in Aquila the Eagle, and is much closer than Deneb; it lies within about 13 light years of our Sun. Use your binocs to pick up many clusters in this rich region of our own Cygnus spiral arm rising now in the east.

To the south, Antares is well up at sunset in Scorpius. It appears reddish (its Greek name means rival of Ares or Mars to the Latins) because it is half as hot as our yellow Sun; it is bright because it is a bloated red supergiant, big enough to swallow up our solar system all the way out to Saturnís orbit! Scorpius is the brightest constellation in the sky, with 13 stars brighter than the pole star Polaris! Note the fine naked eye clusters M-6 and M-7, just to the left of the Scorpionís tail. Beautiful Saturn now sits well north of the stinger on the scorpionís tail.

Just a little east of the Scorpionís tail is the teapot shape of Sagittarius, which lies toward the center of the Milky Way. From a dark sky site, you can pick out the fine stellar nursery, M-8, the Lagoon Nebula, like a cloud of steam coming out of the teapotís spout.

Read past issues of the Sky at Night