For July, the last quarter moon occurs on July 1st. The new moon is on July 8th, but no eclipse of the sun this month. Our next local partial solar eclipse is the new moon in October 2023. Venus is overtaking Mars in the western twilight, and the waxing crescent moon joins the show on July 11th, with the thin crescent to the lower right of Venus, and faint Mars only a moon diameter to the left of Venus. The fatter crescent is above Venus on July 12th, with Regulus in Leo just to the left of the Moon. Fine phase to capture earthshine on the moon’s dark upper side. The first quarter moon is July 17th. The Full Moon, the Thunder or Hay Moon, is July 23rd. That same night, the moon is just to the right of Saturn two hours after sunset, and just below much brighter Jupiter on July 25th. The moon is again last quarter on July 31st; note this interval from one phase to its next recurrence is the moon’s synodic period, of 29.5 days.
Mercury is at greatest western elongation in the dawn sky on July 4th, but disappears into Sun’s glare by midmonth. Venus dominates the dusk, and overtakes most, smaller, and much fainter Mars on July 12th, passing only ½ degree (the diameter of the disks of the Sun and Moon to our naked eyes!) on July 12th, the same evening the waxing crescent moon lies to the upper right of the pair. Great photo op! By the end of the month, Mars is getting lost in the sun’s glare in the NW twilight, to disappear behind the Sun for several months. Both Jupiter and Saturn rise soon after sunset in the SE, with Saturn coming to opposition on August 1st, and Jupiter about two weeks later. Small scopes can catch Saturn’s rings and large moon Titan, and Jupiter’s four large moons, all larger than Pluto or our Moon, and its still impressive Great Red spot.
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; 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.
There is also a video exploring the July sky on the Hubble Space Telescope website at: http://hubblesite.org/explore_astronomy/tonights_sky/. Sky & Telescope has highlights at http://www.skyandtelescope.com/observing/astronomy-podcasts/ for observing the sky each week of the month.
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.
This is the Sagittarius Dwarf Galaxy, now colliding with the Milky Way in Sagittarius in the summer sky. It lies on the far edge of our own barrel spiral, and may account for the formation of our bar. 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. 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. Jupiter and Saturn both lie east of the teapot, on the border with Capricornus.
