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The Night Sky of July

Dr. Wayne Wooten
Professor of Astronomy

For July 2018, the waning gibbous moon passes north of Mars in the morning sky on July 1st. Look how bright Mars appears this morning. The earth is overtaking Mars, making it much closer, bigger, and brighter than it appears normally. The moon is third quarter on July 6th, and new on July 12th. This new moon does pass in front of the sun, but only in Australia is a partial solar eclipse seen. 40 minutes after sunset on July 14, the very slender crescent moon passes just above Mercury in the SW twilight; binocs are recommended!

The next evening gives a great photo op with the crescent moon passing just north of Venus in the evening sky. The moon is first quarter on July 19th. The waxing gibbous moon passes just north of Saturn on July 24th. The full moon, the Thunder Moon, is again north of much brighter Mars on July 27th. Mars is at opposition on July 26th, the closest and brightest it has been since August 2003. And the full moon is totally eclipsed as well, but only for the eastern hemisphere, alas! Quite a month for stargazers!

This July Mercury is visible in the SW twilight below Venus early in the month, with greatest elongation on July 11th. Before it passes between us and the sun, try first spotting it low in SW, then much brighter Venus above it, then turn to spot bright Jupiter in Libra in the south, then further east Saturn above the teapot of Sagittarius, and then Mars in Capricornus rising in SE just before Mercury sets. It is very rare to have all naked eye planets visible at once!

Venus dominates the western evening sky, and should be easily found in daylight on June 15th, with the crescent moon guide to the lower left of it just before sunset. Telescopically it is a gibbous bright disk, 70% sunlight now. No other details are noted with amateur scopes alas.

Mars is in Capricornus, Telescopically the south polar cap is the easiest feature to see, but shrinking daily. Opposition is on July 26th, so this is the best time to observe the red planet since 2003. Our featured photo is when Mars was still gibbous in phase, the south polar cap was prominent at the bottom of the disk, and the dark feature Syrtis major in center of the disk. Since Mars is so small even when fully lit at opposition on July 26th, use your highest power and hope for steady seeing to spot detail like this during the next few months!

Jupiter is well placed for evening observers in Libra. It was at opposition on May 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 unusually red now, and 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 June 27th. 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.

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