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The Night Sky of July

Dr. Wayne Wooten
Professor of Astronomy

For July 2019, the new moon occurs on July 2nd. On the 3rd, the very young crescent lies below the planets Mars and Mercury in twilight, about 40 minutes after sunset. Use binocs. The next evening, the waxing crescent is to the upper left of the planets; Mars is fainter, to the right, and brighter Mercury to the left. The first quarter moon is on July 9th. The waxing gibbous moon is right of Jupiter on July 12, and to the left of it on July 13th. It is just to the right of Saturn on July 15th. The full moon, the Hay Moon, is on July 16th, and gives a partial eclipse for observers on the other side of the world.

While the naked eye, dark adapted by several minutes away from any bright lights, is a wonderful instrument to stare up into deep space, far beyond our own Milky Way, binoculars are better for spotting specific deep sky objects. For a detailed map of northern hemisphere skies, visit the www.skymaps.com website and download the map for July 2019; it will have a more extensive calendar, and list of best objects for the naked eyes, binoculars, and scopes on the back of the map. There is also a video exploring the July sky from the Hubble Space Telescope website at: http://hubblesite.org/explore_astronomy/tonights_sky/. Sky & Telescope has highlights at http://www.skyandtelescope.com/observing/astronomy-podcasts/ for observing the sky each week of the month.

In July, Mercury, Venus, and Mars are all to close to the sun for convenient viewing, but the outer giants Jupiter and Saturn are at their best. Jupiter is well placed for evening observers in Ophiuchus. It was at opposition on June 5th, and is now well up in the SE as twilight falls. Any small scope will also spot its four Galilean moons. The Great Red Spot is undergoing great changes now, perhaps disappearing? It should also be spotted among its clouds at 100X with even small scopes.

But the most beautiful object in the sky is Saturn, which came to opposition in Sagittarius on July 9th. It is not quite as open as last year. Look closely for its large moon Titan, and also perhaps for smaller moons Dione, Rhea, and Tethys. Download the program Stellarium at www.stellarium.org and you can zoom in on the planets to find the layout of the moons of Jupiter and Saturn at any moment.

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 Dipper’s 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 Sagan’s 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 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 Saturn’s 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 Scorpion’s tail. Beautiful Saturn now sits well north of the stinger on the scorpion’s tail.

Just a little east of the Scorpion’s 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 teapot’s spout.

Read past issues of the Sky at Night