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30 May 2017

June Astronomy: Jupiter and Saturn Frolic in the Evening, While Venus Shines at Dawn

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Mid-June finds bright Jupiter high in the south-southwest at dusk, and Saturn low in the southeast, some 70 degrees apart. At dawn, Venus gleams in the east, while Saturn is low in the southwest. The moon forms attractive pairings with various planets and stars here and there throughout the month.

In our June evening twilight sky, bright Jupiter stands high in the south to southwest at dusk, with Spica nearby, to its lower left. As Jupiter ends retrograde motion against background stars in early June, it reaches a maximum distance of just more than 11 degrees west-northwest of Spica. Keep watch this summer, until Jupiter passes just 3 degrees north of Spica on Sept. 11. By then, they’ll be low in the west-southwest at dusk. After that, the next time Jupiter passes Spica will be during their triple conjunction in 2028-2029.

Also in June, we find Saturn rising in the southeast, to the lower left of Antares. Saturn is at opposition to the sun on the night of June 14-15 and is visible all night. In 2017, Saturn’s rings are tipped 27 degrees from edge-on, the greatest angle possible, with their northern face in view.

This year, these inspiring showpiece planetsJupiter with its cloud belts and four bright satellites discovered by Galileo, and Saturn with its spectacular rings and bright moon Titan in a 16-day orbit—are conveniently visible at dusk from mid-June through mid-September. Capture telescopic views of both planets in a single session! In coming years, as their opposition dates shift later, the window of dates to see both planets in the early evening starts about 12 days later each year, while the end of the window shifts about one month later annually. By 2020, both giant planets will be seen together in early evening skies from mid-July through December. The autumn of 2020 will be a fascinating time to watch these planets gradually close the gap between them—until they’re just 0.1 degree apart on Dec. 21, their closest pairing since 1623, during Galileo’s time. So, mark Dec. 21, 2020 on your calendar!

In June, you’ll need binoculars—and no mountains in the way—for final glimpses of faint Mars sinking into the west-northwest evening twilight glow. Look for it to the lower right of the “Twin” stars of Gemini, Pollux and Castor. In the eastern sky, watch for Altair rising to the lower right of Vega and Deneb, completing the Summer Triangle, while Arcturus climbs to its high point south of overhead. Summer begins on June 20 at 9:24 p.m., when the sun is directly overhead at the Tropic of Cancer. Earlier that day, the Coachella Valley observes the year’s highest sun passing, about 10 degrees south of overhead, at 12:48 p.m.

The appropriately named Summer Triangle is up all night from late June through early August. Whenever the Summer Triangle is high in a dark sky, the Milky Way will be in fine view, with one of its brightest star clouds inside the triangle, along the axis of the Northern Cross, or neck of Cygnus, the Swan. Binoculars will readily resolve that misty patch of light into multitudes of stars.

In June’s morning twilight, Venus is still brilliant in the east. Telescopes show it half-full early in the month, when it’s near greatest elongation, 46 degrees from the sun. Using binoculars, look to Venus’ lower left, low in the east-northeast, early in the month to catch departing Mercury, and later to catch emerging Aldebaran. Capella is the bright star ascending in the northeast. The Summer Triangle of Vega, Altair, and Deneb passes west of overhead. Fomalhaut is low in the southeast to south. Two bright stars depart the predawn sky in early June: Arcturus in the west-northwest, and Antares in the southwest. Saturn sinks to the horizon by month’s end, but you can catch it higher by looking earlier, before dawn twilight gets underway.

The moon and planets in June: On the evening of June 3, the waxing gibbous moon passes closely north of Jupiter, and on the following evening, more widely north of Spica. The moon passes the apogee of its orbit on the afternoon of June 8. That evening, it appears widely north of Antares, and on the next morning, the most distant full moon of 2017 appears several degrees to the lower right of Saturn, in the southwest. On the evening of June 9 through dawn on June 10, the moon, just past full, remains in close company with Saturn all night. Saturn is itself at opposition five nights later, on the night of June 14-15. By then, the moon rises just before midnight, so shift your viewing time to predawn to follow the rest of the moon’s cycle.

The last quarter occurs on June 17. On June 20, the waning crescent moon is a few degrees to the upper right of Venus. The next morning, June 21, the moon appears several degrees to the lower left of Venus, and to the lower right of the Pleiades star cluster. On June 22, the moon’s final morning, look for the 4 percent crescent rising in the east-northeast just more than an hour before sunrise. Can you spot Aldebaran, eye of Taurus, closely to the lower left of the moon? Less than 39 hours remain until the new moon, at 7:31 p.m. on June 23.

This graph of planets’ rising times below shows the moon rising closer to the time of sunrise each successive morning June 17-22, and just before Venus rises on June 20. Venus itself rises ever farther ahead of the sun until late July.

On June 24, the moon returns to the evening sky. Using binoculars, try for the 25-hour crescent a half-hour after sunset, when it’s 2 percent full and barely above the west-northwest horizon. Binoculars help! A sighting of this crescent ends the month of Ramadan and begins the next, Shawwal, in the Islamic calendar. On the next evening, June 25, spotting the moon will be much easier, when it’s 6 percent full and well to the left of Pollux and Castor. On the evening of June 27, there will be a close pairing of the moon and Regulus. The moon occults the star in the early afternoon from Hawaii, and in the early evening from Ecuador and Peru. From California, the crescent slips south of the star in late afternoon, and appears to the left of the star at dusk. By sunset on June 30, the moon has just passed first quarter phase and appears half full. That evening, bright Jupiter appears a few degrees southeast of the moon, and Spica several degrees southeast of Jupiter. It’s an ideal evening for telescopic views of the moon and Jupiter, and of the third-magnitude star very close to the moon! At 100-power, the star splits into a tight, matching pair of stars, with a period of revolution of 169 years. The pair will change noticeably during a lifetime, as it slowly widens and revolves away from its present north-south orientation.

This graph of planets’ setting times below shows the moon setting successively later each evening June 24-29: Just before twilight ends on June 25; about the same time Regulus sets on June 27; and more than four hours after sunset, just before Jupiter and Spica set, on June 29. Regulus will set in evening twilight by late in July, while Jupiter and Spica won’t sink into twilight until sometime in September.

Check the website of the Astronomical Society of the Desert at www.astrorx.org for a listing of our star parties at Sawmill Trailhead, our high altitude site (at 4,000 feet elevation—wear warm clothes), starting at dusk on Saturday, June 24, July 22, Aug. 19, Sept. 23, and Oct. 14.  Monthly star parties at the Visitor Center of the Santa Rosa and San Jacinto Mountains National Monument will resume Oct. 28. The society’s website includes maps and directions.

Also, check out the Sky’s the Limit Observatory and Nature Center in Twentynine Palms, at skysthelimit29.org.

Finally, remember the total solar eclipse coming to some parts of the country—but, alas, not here—on Monday, Aug. 21. See last month’s column for a list of Internet resources.

Robert C. Victor, formerly a staff astronomer at Abrams Planetarium at Michigan State University, is now retired and enjoys providing sky watching opportunities for school children 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. Dr. Jeffrey L. Hunt, a retired planetarium director now living in the Chicago area, did the planet charts below. He has taught astronomy and sky watching to all ages. He studied astronomy education at Abrams Planetarium at Michigan State University and writes an astronomy blog at jeffreylhunt.wordpress.com.

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