The night skies of July are exceptionally interesting because of its array of bright planets.
As the sun sets, look to the east-southeast for the appearance of Jupiter and Saturn. Gigantic Jupiter, enveloped by a deep atmosphere and icy cold, shines brilliantly, while Saturn, appearing only about 1/13 as bright, still glows conspicuously with a sedate yellow-white hue. Saturn was the Roman moniker for the Greek god Cronus, the personification of “Father Time.” Ancient sky watchers named the planets for their most notable aspect, and Saturn seemed to move sluggishly compared to the other deities, taking almost 30 years to make one complete circuit of the sky. How amazed they would have been if they could have viewed Saturn through a telescope and gazed upon its magnificent system of rings.
And have you ever wondered how the ancient Romans happened to name Jupiter after the most powerful of gods, although they knew nothing of the planet’s physical characteristics?
During the middle of the night, Mars comes over the eastern horizon. If you have been following it since the beginning of the year, you no doubt noticed how it has gradually increased in radiance as it continues to approach our Earth. From the beginning of July until the end of August, Mars will more than triple in brilliance, appearing almost sinister, staring us down with a distinctive fiery-hue.
During the predawn hours, Venus blazes like a night-light in the east-northeast, “keeping company” in mid-July with the bright orange star Aldebaran and on July 17th, engaging with the moon to produce eye-catching celestial tableaus.
Late July into early August also sees a moderately-good apparition of Mercury. Between July 20th and August 4th, Mercury will brighten from magnitude +0.5
to -1, while rising 60 to 70 minutes before sunup.
In our schedule, remember that when measuring the angular separation between two celestial objects, your clenched fist held at arm’s length measures roughly 10-degrees. Here, we present a schedule below which provides some of the best planet viewing times as well directing you as to where to look to see them.
Mercury – which passed inferior conjunction with the sun on June 30th, climbs into a fine dawn apparition in the latter half of July. From July 20th through the 31st, observers around 40° north who go out a half hour before sunrise will find Mercury at least 10° above the east-northeast horizon. Bring binoculars. Mercury attains its greatest elongation, 20° west of the sun, on July 22nd. On that date it’s a 37% illuminated crescent shining at magnitude +0.3. From the 22nd through the 27th, Mercury will stand 24° to 25° to the lower left of Venus and continue brightening about 0.1 magnitude per day. By August 4th Mercury will rise only an hour before the sun, but at magnitude -1.1 should still be visible.
Venus – During July, rockets up into a superb morning apparition. At month’s start, this dazzling planet rises about 2 hours before sunup, but by month’s end it does so 3¼ hours before sunup. As seen from around 40° north latitude, Venus stands about 21° above the eastern horizon at sunrise on July 1st and 35° high on July 31st. Telescopes show the disk of Venus shrinking in July as its phase thickens from 20 to 43 percent illuminated.
It reaches a peak in its great brightness, known as “greatest illuminated extent,” on July 10th, flaming to magnitude -4.7. It’s a spectacular sight for both naked-eye and telescope users during July, with the only drawback being that you’ll need to rouse yourself out of bed before the early summer sunrise in order to see it. Venus is near the end of its retrograde loop, temporarily parked in the midst of the face of Taurus the Bull (the V formed by the orange 1st magnitude star Aldebaran and the giant Hyades star cluster). Venus is just 1° from Aldebaran on July 11th, 12th and 13th – a marvelous sight.
Facing due east about an hour before sunrise on July 17th, you’ll see the moon, a star and a planet forming a stretched-out, inverted isosceles triangle. Dazzling Venus marks the vertex angle, while Aldebaran and a slender crescent moon mark the base angles. The moon sits 3° to the upper left of Venus and Aldebaran is 3° to the upper right. By the end of July, Venus has sped a full 13° away to the east of Aldebaran.
Earth – is at the aphelion of its orbit; farthest from the sun for the year (94,507,635 miles) on July 4th at 7:35 a.m. Eastern daylight time. We’re then 3% farther from the sun than at perihelion in January.
Mars – looms ever nearer, brighter, and more imposing as it approaches its early October opposition and rendezvous with Earth. Currently burning like a fiery fleck of coal at magnitude -0.7, it’s 69.7 million miles away. By month’s end, it will have moved 9.8 million miles closer and will have brightened up to magnitude -1.1. If you look low toward the eastern horizon on July 12th at around 1 a.m. local daylight time, you’ll see a slightly more than half illuminated moon and sitting less than 5° to its upper right will be Mars
Jupiter – will reach opposition to the sun on July 14th. All month it beams at its year’s best magnitude of -2.7. Although Jupiter rises around sunset, the best time to observe it is in the middle of the night, when it is highest in the south. Even then, Jupiter is only about 28° high for viewers at latitude 40° north, so it’s not likely to appear very crisp in telescopes. However, the planet’s disk appears impressively large at this closer-than-average opposition.
Saturn – comes into view low in the southeast during dusk and at the beginning of July climbs to an altitude of 20° by about midnight local daylight time and by 10 p.m. at month’s end. The beautiful ringed planet reaches opposition on the night of July 20th, on its way to becoming an early-evening showpiece of late summer and early fall.
There’s a full moon on July 5th at 12:44 a.m. EDT. There will also be a penumbral eclipse of the moon. A non-event, since less than fourth-tenths of the moon will slide through the southern edge of the Earth’s penumbra . . . not enough to create any kind of noticeable darkening on the moon’s disk.
However, one thing that you certainly will notice later that evening are the two largest planets flanking the moon as it ascends in the southeast late evening sky. Sitting 4° above and slightly to the right of the moon is Jupiter and situated about 4½° to the upper left of the moon and just over a half dozen degrees to Jupiter’s lower left is Saturn.
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Joe Rao serves as an instructor and guest lecturer at New York's Hayden Planetarium. He writes about astronomy for Natural History magazine, the Farmers' Almanac and other publications in New York's lower Hudson Valley. Follow us on Twitter @Spacedotcom and on Facebook.