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The Night Sky of July

Dr. Wayne Wooten
Professor of Astronomy

For July, the Moon will be a waning crescent in the morning sky during the first week, and then new on July 8th. The waxing crescent moon passes six degrees south of Venus on July 10th; note the nice binocular view of the Beehive cluster, M-44, between Venus and the Moon this evening! The first quarter moon passes just three degrees south of Saturn on July 16th. The Full Moon is on July 22nd, and is called the Hay or Thunder Moon in Native American tradition. The last quarter moon is on July 29th, rising about midnight.

Venus dominates the western evening sky in July, but Mercury and Jupiter are now lost in the sunís glare. Through the telescope, Venus is a small gibbous disk, still on the far side of the sun. Its disk is bright but featureless, as we only see the top of its sulfuric acid cloud deck from earth visually. It passes 1.1 degrees north of bright Regulus in Leo on the evening on July 22nd.

Mars is moving rapidly eastward in the dawn sky, and overtakes Jupiter on July 22nd. It does not reach opposition for good telescopic observing until about a year from now.

Saturn is well placed for evening viewing in the southern sky after sunset. The rings are open up to 17 degrees, and a telescopic treat to be savored at our public gazes. Itís large moon Titan is as big as the planet Mercury, and is visible in most any telescope. Three middle sized moons, Rhea, Tethys, and Dione, are all about half as big as our own moon, and visible in scopes six inches or larger in aperture.

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 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.

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; like Vega, it lies within about 25 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. Our photo for this month shows the two clusters as they appear in binoculars.

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 binocs, and resolves well with any scope 4" aperture or larger.

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