July highlights include: The “Evening Star” Venus is near a bright zodiacal star on several evenings. Mars in beautiful the predawn star fields of Taurus. There are lunar escorts at both dusk and dawn.
In the evenings this summer, Venus dominates, gradually brightening all season, even as it sinks lower into twilight. Venus is becoming a good target for low-power telescopic viewing. On July 1, the planet’s gibbous disk appears 69 percent illuminated and 16” (arcseconds) across. By July 31, the planet’s disk is 56 percent full and has grown to 21”. Venus will change from gibbous through half-full to crescent in August, and on Sept. 23-24 will reach greatest brilliance at magnitude -4.8, displaying a 21 percent crescent, 43” across.
On July 1, in deepening twilight about one hour after sunset, Venus shines at magnitude -4.1, low in the western sky. Jupiter, of magnitude -1.8, is 21° to the lower right of Venus as the month begins, and will slip out of naked-eye view after a few more days, owing to the faster orbital motion of Earth around the sun. If you have a place where the west-northwest horizon is unobstructed, use binoculars to try to keep track of Jupiter until July 14, when you may locate a very thin, young crescent moon. That’s only 15 days before Jupiter’s solar conjunction on the 29th, so it won’t be easy.
As the sky darkens on July 1, look for Regulus, heart of Leo, the Lion, within 9° to the upper left of Venus. On July 9, Venus passes just 1° north (to the upper right) of Regulus, and for five days before and after (July 4-14), Regulus appears within 6° of Venus, in the same field of view of binoculars. Follow the changes as Venus shifts its position eastward by slightly more than 1° per day.
The brightest stars visible at dusk in July are of zero-magnitude: golden-orange Arcturus, high in south-southwest to west-southwest, and blue-white Vega, high in the east-northeast. Additional bright stars, of first magnitude, are Altair and Deneb, to the lower right and lower left of Vega, completing the Summer Triangle with it; the red supergiant star Antares, in the south-southeast to south, marking the heart of Scorpius, the Scorpion; and Spica, the spike of grain in the hand of Virgo, about 33° below Arcturus.
The Summer Triangle—well named—is visible during all of July’s nighttime hours: in the east at dusk, nearly overhead in the middle of night, and in the west at dawn. Arcturus and Spica can be found by extending the curve of the Big Dipper’s handle: “Follow the arc to Arcturus, and drive a spike to Spica.”
The moon on July 2 rises about as evening twilight ends and spoils Milky Way viewing. By July 4, the waning gibbous moon rises late enough to allow excellent views of the Milky Way star clouds. Note especially the Cygnus Star Cloud inside the Summer Triangle, along the Swan’s neck, and the Greater Sagittarius Star Cloud, appearing like steam rising from the spout of the Teapot to the left of the Scorpion. Scorpius, at its highest when due south, is my summer favorite for star-hopping with binoculars. At least two stars can be viewed simultaneously, making it easy to trace out the entire constellation, while pausing to take in its beautiful double stars and star clusters. Note the fine star cluster Messier 7, to the upper left of the Scorpion’s tail. Fine Milky Way viewing in dark, moonless skies continues through July 14, or through July 20 if you wait until after moonset.
The new moon occurs on July 14 at 2:44 a.m. Using binoculars, it’s possible to spot a very thin, 1 percent young crescent moon on the evening of the same date, July 14. Look very low in the west-northwest about 25 minutes after sunset, within 34° to the lower right of Venus and 1.2° to Jupiter’s upper right. If you spot the crescent, note the time, and the moon’s age, or the time elapsed since new moon. In Reno, it will be a few minutes more than 18 hours. Another way to know where to find the moon is to note the sun’s position shortly before sunset that evening: When it’s 2°-3° above the true, unobstructed horizon, wait about 41-42 minutes, and look for the moon in almost the same place!
On the following nights, the moon will set later, in a darker sky, and you can look for it a full hour after sunset. On July 15, find the 4 percent crescent 20° to the lower right of Venus, and 13° to the lower right of Regulus. On the 16th, the 10 percent crescent is 7° to the lower right of Venus, and just 2° to the right of Regulus. On the 17th, the 18 percent crescent is 7° to the left of Venus. Continuing east through the belt of zodiac constellations, by July 20, the 42 percent fat crescent passes 3° to the lower left of Spica. Four days later, on the 24th, the 83 percent gibbous moon passes 3°-4° to the lower left of red Antares.
On July 28, the moon is just short of full and rises just before sunset. On the 29th, the moon has passed full and rises just after sunset. Enjoy the moonrises, which occur not much later each evening, because of the low angle of the moon’s orbit relative to the horizon during evenings at this time of year. On each successive evening, the moon rises noticeably farther north (to the left). Even on July 31, the waning gibbous moon still comes up before the end of twilight.
In July’s morning sky, the brightest stars are Vega, in the west-northwest, and yellowish Capella, in the northeast. Other bright objects are Altair and Deneb, completing the Summer Triangle with Vega; Fomalhaut, mouth of the Southern Fish in the southern sky; and Aldebaran, eye of Taurus, low in the east.
The easy naked-eye planets are yellowish Saturn, of magnitude +0.8 to +0.6 and well up in the southeast, and reddish Mars, of magnitude +1.3, low in the east. On July 1, Mars appears within 5° to the lower right of the Pleiades, and within 10° above similarly colored Aldebaran. Throughout July, Mars shifts east against the Taurus backdrop by 0.7° daily, so when it appears close to the Pleiades, Aldebaran and the Hyades early in month—wonderful sights through binoculars!—and the Bull’s horns at end of July, it’ll be easy to notice the changing position day by day. Uranus appears as a 5.7-magnitude “star” visible in binoculars within 2° of Mars during July’s first week. They’re closest, with Uranus within 11 arcminutes (less than 0.2°) above Mars, on the morning of July 4.
The waning gibbous moon, just more than half-full in the morning sky and nearing last quarter phase, passes Saturn on July 7. This month, Saturn’s rings open to 9° from edgewise before the Earth’s orbital motion temporarily carries us a bit back toward the ring plane.
Saturn begins retrograde, or westward motion against the stars, on July 26. The planet then forms a nearly isosceles triangle with Delta and Epsilon in Pisces, fourth-magnitude stars 3.5° apart and each nearly 5° from Saturn. The planet barely moves this month, but its nearly 7° westward shift by the end of retrograde on Dec. 10 will certainly be noticeable.
The waning crescent moon, 13 percent full, will form an unusual south-to-north alignment with two red objects in the predawn on July 11: Mars, 4.7° to the south (lower right) of the lunar crescent, and Aldebaran, 5.4° to the south of Mars. The line is 10° long, oriented at nearly a right angle to the plane of the zodiac.
The next two mornings, Mars passes closest to Aldebaran, at a distance of 5.3°. Meanwhile, the moon moves on to become a 6 percent crescent on July 12, nearly 15° to the lower left of Mars and close to 1.7-magnitude Elnath, tip of the Bull’s northern horn.
The 1 percent crescent moon, 29° to the lower left of Mars on July 13, rises closer to sunrise and requires observation around mid-twilight, 51 minutes before sunrise near Reno. If you spot the old moon on the morning of July 13, a sighting would occur within 22 hours before the new moon of July 14. That would be a nice accomplishment! The sighting of the young crescent at dusk on July 14, as described in the account of evening events, would be even more challenging. If you see the opposing crescents on consecutive days, you will be in rare company. Include details in your report: descriptions, times of your first and last sightings of the moon on each date, your location, equipment used for each sighting, and sky conditions.
By the date of the full moon on July 29, the moon returns to the southwest morning sky. Before then, a well-known constellation up nearly all night in December will start to appear in the east at dawn. Robert Frost described the scene well, in the opening lines of his poem, The Star Splitter:
You know Orion always comes up sideways.
Throwing a leg up over our fence of mountains …
Look for red Betelgeuse and blue Rigel, with Orion’s vertical three-star belt between. Farther to the left, watch for the sideways rising of the Twins Castor above Pollux.
Many of the sky events described above are illustrated on the Abrams Planetarium Sky Calendar. For $12 per year, subscribers receive quarterly mailings, each containing three months of calendars and evening star maps. Subscription info and a free printable sample are available at abramsplanetarium.natsci.msu.edu/sky-calendar/index.aspx.
Robert Victor was a staff astronomer at Abrams Planetarium at Michigan State University. He is now retired and enjoys promoting sky watching to folks of all ages. Robert Miller, who provided the twilight charts, did graduate work in planetarium science and later astronomy and computer science at Michigan State University, and remains active in research and public outreach in astronomy.
