The Night Sky of July

Dr. Wayne Wooten
Professor of Astronomy

For July, the Moon will be waning gibbous as the month begins. The Full Moon on June 26th will actually produce a partial lunar eclipse, the beginning of which will be visible just before sunrise in the SE US. At 5:30 AM, the moon starts to enter our dark umbral shadow, but it sets at 5:50, with only a slight bite taken out of its edge.

The first two weeks of July will thus find the Moon at waning in the morning sky. The last quarter moon passes about six degrees north of Jupiter on July 4th. The new moon is on July 11th, and produces a total solar eclipse, visible from Easter Island in the South Pacific, but nothing observable here. The next total solar eclipse for us in the US is August 21, 2017. The waxing crescent moon on July 14 passes 4 degrees south of Venus; she passed Regulus in Leo on the 10th, so this makes a nice triangle in the west. The moon passes five degrees south of red Mars on the 16th, and just below Saturn a few hours later. Mars overtakes Saturn at month’s end in Virgo. This full moon is the Hay or Thunder moon, depending on the culture, and takes place on July 26th.

Venus dominates the western sky, and moves higher in Leo throughout this month. She is 71% sunlit as July begins, and 16 arc seconds in diameter, but as she overtakes us, is grown to 19 arc seconds, but 60% lit as July ends. Mars is faint and distant, with only a tiny five arc second disk noted in telescopes, but it moves rapidly through Leo and into Virgo by month’s end, passing Saturn on the 31st. Saturn is named for the god of time (Chronos in Greek) because he moves so slowly. Saturn’s rings now opened about four degrees, so appear very thin, almost edge-on. It disappears into the Sun’s glare by August, so observe it early in July right after sunset, before it gets too low.

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. Saturn lies just below the right triangle that marks the lion’s hindquarters. 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. It is above Corvus, in the arms of Virgo, where our large scopes will show members of the Virgo Supercluster, a swarm of over a thousand galaxies about 50 million light years away from us.

To the east, Hercules is well up, with the nice globular cluster M-13 marked on your sky map and visible in binocs. It closely approximates that amateurs will see through the eyepiece with a 6" telescope on a dark clear night. It too looked very fine at our Sky Interpretation session on June 11th. Several other good globular clusters are also shown and listed on the best binoc objects on the map back page.

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 bottom of the parallogram of Lyra is the famed Ring Nebula, M - 57. This planetary nebula is easy to find in small scopes midway between the two bottom stars of Lyra, and is marked on your star charts.

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 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. Both are spectacular with binocs.

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. 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.

Later in the July evenings, giant Jupiter dominates the SE sky. It rises about 10 PM by the end of July in Aquarius, and is at opposition in mid September, rising at sunset. Any small scope will reveal what Galileo marveled at in 1609; four large moons, all bigger or similar to ours in size, orbit it in a line along Jupiter’s equator. So get out the old scope, and focus on Jupiter for a constantly changing dance of the moons around the giant world.

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