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The Night Sky of July

Dr. Wayne Wooten
Professor of Astronomy

For July, the Moon will be Full Moon, the Hay or Thunder Moon, is on July 2th. The last quarter moon rises about midnight on July 8th. The moon is new on July 16th. The waxing crescent just after sunset joins a fine grouping of Jupiter (on bottom) and Venus on the evening of July 18th. The moon is first quarter on July 24, and passes 2.4 degrees north of Saturn on July 26. The Blue Moon, the second full moon in a month, is on July 31st.

Venus and Jupiter are only.34 degrees apart as July begins, and in the same low power telescopic field at 30-50X. In an interesting coincidence, both appear 32" of arc across, but Venus appears as a crescent, 33% sunlit, while Jupiter is fully lit and surrounded by its four large moons orbiting around the planetís equator. By the end of July, Venus is much closer to us and bigger, 51" of arc across but a crescent only 10% sunlit. It is retrograding back between the Sun, and us, and passes 6.4 degrees south of Jupiter on July 28th. Jupiter is also moving slowly, approaching Regulus the brightest star of Leo by monthís end. The waxing crescent moon makes a spectacular grouping with the triangle of Venus (brightest, lower left), Regulus above it, and Jupiter to right on the evening of July 18th; compare the phase of Venus and the Moon in binoculars and small scopes this evening.

Saturn is also well placed for evening observing in July, just above the claws of Scorpius in the SE. It is tilted 24 degrees toward the Sun, and us, and the rings and moons are the most beautiful sight in the telescopic sky.

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. Saturn lies in Virgoís eastern feet 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 binoculars.

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 lies in Aquila the Eagle, and is much closer than Deneb; it lies within about 13 light years of our Sun. Use your binoculars 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.

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. The fine globular cluster M-22 sits just NE of the star in the lid with binoculars, and resolves well with any scope 4" aperture or larger.

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