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30 Jun 2020

July Astronomy: It's a Great Month for Sky-Watching, as Venus, Jupiter and Saturn Reach Peak Brilliance

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Good news for evening viewers! Jupiter and closely following Saturn are rising about a half-hour earlier per week, so by the dates of their respective oppositions, on the nights of July 14 and 20, they reach peak brilliance and will have just risen at sunset. As darkness descends, the beautiful pair of giant planets will be in the east-southeast, in the deep blue part of the sky, opposite the sun’s direction. After their oppositions, Jupiter and Saturn will remain visible in the evening sky until early in January 2021.

If you enjoy the cool of the morning, then centering your outings 60 to 90 minutes before sunrise will give you many planetary visual treats—including Venus reaching peak brilliance in the east. Starting July 1, Venus slowly moves across the Hyades star cluster until passing just 1 degree north of Aldebaran July 11 and 12. By then, Jupiter and Saturn are nearly at opposition, so they’re getting low in southwest.

Through a telescope—or even through binoculars if you look around sunrise or in the daytime—Venus offers up crescent phases, 19 to 43 percent full this month, but shrinking in apparent size as the planet recedes from Earth. Jupiter, with its cloud belts and four bright Galilean moons, and Saturn, with its amazing rings, are always pleasing. To get a good view of the surface details of Mars requires more magnification: A six-inch reflecting telescope working at 200x has recently shown me excellent views of Mars’ bright south polar cap of frozen carbon dioxide.

A permanent surface feature first noted on Mars by Dutch astronomer Christiaan Huygens in 1659 still can be seen as a dark, roughly triangular patch of basaltic rock now known as Syrtis Major. As Mars rotates on its axis once each 24.65 hours, Syrtis Major will appear just north of the center of the Martian disk, on Tuesday, July 28 at 1:28 a.m., and about 39 minutes later each morning.

If you’re looking an hour before sunrise, and you have unobstructed views, Jupiter and Saturn will remain above your southwestern horizon for several days after their oppositions. Meanwhile, Mars is high in the south-southeast. On July 16 and 17, a waning crescent moon forms beautiful gatherings with Venus, Aldebaran and the Hyades star cluster; on July 18 and 19, the thin old moon appears near Mercury, as the innermost planet brightens low in the east-northeast and emerges from the sun’s glare.

In the evening sky: On July 1, bright Jupiter is just rising in the east-southeast at evening mid-twilight, and Saturn, just more than 6 degrees to its east, rises 20-25 minutes later. The waxing gibbous moon appears near Antares on July 1 and 2. On July 4, watch the full moon rising very close to sunset. After nightfall on July 5, catch the moon between Jupiter and Saturn, below the line joining the two giant planets. Jupiter and Saturn reach opposition as Earth overtakes them; thereafter, for the rest of 2020, they are more favorably placed for evening viewing.

Elsewhere in the sky at dusk in July, watch Antares reach the south, as the Summer Triangle of Vega, Altair and Deneb climbs high in the east. See golden Arcturus and blue-white Spica move through the southwest quadrant, chasing Regulus nearly to the horizon in the west-northwest. The moon returns to the evening sky as a young crescent very low in the west-northwest at dusk on July 21, and appears within 4 degrees above Regulus on July 22. The moon, nearly half full and approaching first-quarter phase, appears near Spica on July 26; in gibbous phase above Antares on July 29; and nearly full, between and below Jupiter and Saturn, on Aug. 1.

July’s morning sky: On July 1, one hour before sunrise, bright Jupiter is in the southwest, with Saturn 6.1 degrees to its upper left. Mars is high in the southeast. Brilliant Venus is in the east-northeast to east, with the reddish first-magnitude Aldebaran, eye of Taurus, 3.4 degrees to its lower left. Views of Venus moving through the Hyades star cluster toward Aldebaran, all in one field of view of binoculars July 1-12, will be spectacular.

From July 5-19, before sunrise, the moon will pass all other seven planets of our solar system. Mercury doesn’t show up until almost the end of that period, and then becomes more prominent after the moon has passed from the scene.

On July 4, an hour before sunrise, the moon is about to set in the southwest to west-southwest. Jupiter is 20 degrees to its upper left, with Saturn 6.2 degrees to the upper left of Jupiter.

On July 5, the full moon is in the southwest, with Jupiter 7 degrees to its upper left, and Saturn 6.3 degrees to the upper left of Jupiter.

On July 8, Aldebaran is within 2 degrees to the lower left of Venus. Watch Venus shift about a half-degree daily the next few mornings, providing spectacular viewing for binoculars.

On July 11, one hour before sunrise, the 64 percent waning gibbous moon is high in the south-southeast, with Mars 5 degrees to its upper left. This morning and tomorrow, Venus appears just 1 degree north of Aldebaran. This is the third and final event of a triple conjunction between the two bodies. The first was visible on the evening of April 14; the second occurred on June 12. This third pairing is well seen, rising in a dark sky some 2 1/2 hours before sunup.

July 12: Find Mars 7 degrees to the upper right of the 55 percent moon, approaching last-quarter phase.

July 14: Jupiter is at opposition, as Earth passes between our solar system’s largest planet and the sun.

July 16: Many spectacular sights this morning! Get outside at least 75 minutes before sunrise, and begin with the 19 percent crescent moon in the east. Brilliant Venus is within 9 degrees to its lower left, with Aldebaran 2.7 degrees to the upper right of Venus, and 6-7 degrees to the lower left of the moon. Binoculars will show stars of the Hyades star cluster between the moon and Aldebaran, and the Pleiades (Seven Sisters) cluster within 8 degrees to the moon’s upper left. Jupiter and Saturn are within 7 degrees, low in the southwest. Mars is high in the south-southeast.

July 17: The 12 percent waning crescent moon is a little north of east an hour before sunrise, in spectacular conjunction with Venus, just 4 degrees to its upper right. It’s not Venus that’s causing the dark, non-sunlit side of the moon to be visible; it’s earthshine! Aldebaran is 3.3 degrees to the upper right of Venus. Using binoculars, look very low in east-northeast 20 degrees to the lower left of moon for Mercury. It’s of magnitude +1.1 and may be difficult to see low in the twilight. By July 21, Mercury brightens to magnitude +0.4 while staying 23 degrees to the lower left of Venus, their least separation for this apparition. Also on July 17, an hour before sunrise, find Mars high in the south-southeast, and Jupiter and Saturn 7 degrees apart low in the southwest to west-southwest.

July 18, an hour before sunrise, see the moon and all five bright planets! The 6 percent crescent moon with earthshine on its dark side is low in the east-northeast. Look 8 degrees to its lower left for Mercury, of magnitude +0.9. Binoculars may still be needed. Venus gleams 16 degrees to the moon’s upper right, with red Aldebaran 4 degrees to the upper right of Venus. Another 4 degrees to the upper right of Aldebaran is the point of the V-shaped Hyades star cluster. Mars is high in the south-southeast. Jupiter is low in the southwest to west-southwest, with Saturn just 7 degrees to its upper left.

If you get out earlier, before the start of twilight, 1 hour 40 minutes before sunrise, with binoculars and good finder charts, you’ll be able to spot Uranus and Neptune.

July 19: It’s the last morning to catch the old moon! If you have a good low horizon toward east-northeast, look for the 2 percent lunar crescent, just risen, 28 degrees to the lower left of Venus. Look for Mercury, magnitude +0.7, 23 degrees to the lower left of Venus, and nearly 6 degrees to the upper right of the moon.

July 20: The five bright planets can be viewed simultaneously. Locally, Mercury (magnitude +0.5) and Jupiter (magnitude -2.7) are 5 degrees above opposite horizons about 55 minutes before sunrise this morning, so you’ll need to seek out a place with unobstructed views if you’re to see five planets at once. Jupiter is very low in the west-southwest, while Saturn (magnitude +0.1), at opposition to the sun, is 7 degrees to the upper left of Jupiter. Mars (magnitude -0.9) is high in the south-southeast. Venus gleams at magnitude -4.6 in the eastern sky, and Mercury is very low in the east-northeast, 23 degrees to the lower left of Venus.

For the next week, Mercury brightens by about 0.1 magnitude daily, and the viewing time to find Mercury and Jupiter at equal altitudes shifts about 2-3 minutes earlier daily. Mercury reaches greatest elongation, 20 degrees from the sun, on July 22, and reaches its greatest elevation in our local morning twilight skies July 24-26, brightening through magnitude 0 on July 23-24, through magnitude 01 on Aug. 2-3.

The Abrams Planetarium monthly Sky Calendar now has over 3,000 subscribers nationwide. For more information, visit www.abramsplanetarium.org/skycalendar.

The next star party hosted by the Astronomical Society of the Desert, tentatively scheduled for July 18 at Saw Mill Trailhead, might be cancelled to prevent the spread of COVID-19; visit the club’s website at www.astrorx.org.

Wishing you clear skies!

Robert Victor was a staff astronomer at Abrams Planetarium at Michigan State University. He is now retired and enjoys providing informal sky watching opportunities for folks in and around Palm Springs. Robert D. Miller 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.

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