The Night Sky of July
Dr. Wayne Wooten
Professor of Astronomy
For July, the Moon will be new on July 1st. It creates a partial solar eclipse, visible only in Antarctica. We have no solar eclipse visible from Pensacola until August 21, 2017, when we will witness a 82% coverage about 1 PM. The moon, almost first quarter, passes seven degrees south of Saturn on July 7th. The Full Moon on July
15th is called the Thunder or Hay Moon. The last two weeks of July will thus find the Moon at waning in the morning sky. The last quarter moon passes about five degrees north of Jupiter on July 23rd. The waning crescent moon passes a degree south of Mars in the morning sky on July 27th. The second new moon is on July 30th.
Both Mercury and Venus lie too close to the Sun for observing this month. Mars is faint and distant and in the morning sky. Jupiter is in Aries, rising about midnight. Saturn is the only planet now in the evening sky, and we will lose it to the Sunís glare by September, so observe it early in July right after sunset, before it gets
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.
It was just south of the end of the handle of the Big Dipper that we find the famed Whirlpool Galaxy, M-51, visible with binoculars. It was the first galaxy to be resolved into a spiral, and any scope 8" or larger under clear dark skies will reveal this famed structure of colliding galaxies.
Then in June we witnessed a supernova (see photo), shown in the before and after. Supernovae like these are normally rare, but this galaxy has sported three in the last two decades! These explosions liberate into the interstellar median elements heavier than helium, made in the cores of giant stars such as Antares; the carbon in
your DNA as well as most of the elements of earth and your body are products of these stellar suicides.
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 next to the star gamma Virginis . 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
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. 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 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. Both are spectacular with binocs.
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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