The Night Sky of July
Dr. Wayne Wooten
Professor of Astronomy
Escambia Amateur Astronomers' Association
For July, the Moon will be full on July 7th. The first week of July will thus find the Moon at waxing gibbous phase in the evening sky. This full moon is the Hay or Thunder moon, depending on the culture. It finds the moon about 3 degrees south of brilliant Jupiter, low in the
south in Capricornus on July 9th. Last quarter moon is on July 15th. The last three weeks of July will be good times for deep sky observing, with no moon or a waxing crescent.
The waning crescent moon passes Mars in the morning sky on July 18th, then much brighter Venus on July 19th. The new moon on July 22nd is very important in Asia, as it will produce the longest total solar eclipse of this century from India through China, with Shanghi lying on the center line
for almost seven minutes of totality. We will have to wait until August 21, 2017 to witness a totality half that long in the US, with Nashville and Charleston, South Carolina lying along that center line for an early afternoon date with darkness.
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, about June
30th visit the www.skymaps.com website and download the map for July 2009; 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. Also available as the next month begins is wonderful video exploring the July 2009 sky, featuring many
different objects, available from the Hubble Space Telescope website at: http://hubblesite.org/explore_astronomy/tonights_sky/.
Saturn is named for the god of time (Chronos in Greek) because he moves so slowly. Saturn's rings are almost edge-on at its 2009 equinox, a fine view not to be repeated for another 15 years. It disappears into the Sun's glare by the month's end, 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 35 degrees 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 rising, with the nice globular cluster M-13 marked on your sky map and visible in binoculars. Several other good globular clusters are also shown and listed on the best binocular 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 binoculars 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 binoculars.
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 binoculars, and resolves well with any scope 4" aperture or larger.
Later in the July evenings, giant Jupiter dominates the SE sky. It rises about 9 PM by midmonth in Capricornus, and is at opposition in mid August, 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.
So get out and enjoy the exciting night sky of July!
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