The Night Sky of July
Dr. Wayne Wooten
Professor of Astronomy
For July, the Moon will be full on July 3rd; this is the Thunder or Hay Moon. The moon is last quarter on July 11th. The waning crescent moon occults Jupiter, as seen from Europe, on July15th, then passes four degrees north of Venus in the morning sky locally.
The new moon will be on July 19th, so the second and third weeks of July find the moon in the morning sky, a great time for evening stargazers to see dark skies in rural settings. On July 24th, the waxing crescent moon passes four degrees south of Mars, then on July 25th, six degrees south of Saturn. The moon is first quarter on July 26th, high overhead in the
evening sky at sunset.
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
Mercury is well placed for evening viewing in the first week of July, at greatest eastern elongation 26 degrees from the sun. Look for it in the west about an hour after sunset, but by the middle of July, it is passing between us and the sun, but no transit this time; next one visible here will be on May 5, 2016. Usually Venus and Mercury pass above or below the
Sun, and if you missed the transit of June 5th, we will not get another one until 2117 for Venus. Obviously Mercury transits are much more common, but less spectacular than Venus transits.
Venus dominates the dawn sky in July, with a close passage just five degrees south of Jupiter on July 1st; the two brightest planets will make a fine sight for early risers. Through the telescope, Venus is a crescent, fattening from 16% lit and 44” of arc across on July 1 to 44% sunlit and 28” of arc across by month’s end, as it pulls away from the earth and sun
in the dawn sky.
Mars is moving rapidly eastward from Leo into Virgo, and catching up to Saturn and Spica by mid August. Jupiter is in the morning sky, rising about 2 AM by July’s end. Saturn is easy to spot in the SE, just north of the bright star Spica in Virgo. The rings are open up to 14 degrees, and a telescopic treat to be savored at our public gazes.
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 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. 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 from us.
The famed Ring Nebula, M - 57
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 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. Bob Gaskin’s shot of this stellar striptease shows the tiny white dwarf star at the center well, but it takes big telescopes to spot visually, while the ring itself is visible even in binoculars.
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.
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