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30 May 2019

June Astronomy: As the Summer Begins, Look to the Skies for Planets at Mutual Opposition

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June evenings will be wonderful for viewing the skies, especially if you stay up late enough until the sky fully darkens. With daylight saving time in effect on these longest days of the year, that might be a tall order!

Mercury starts 16 degrees to the lower right of Mars on June 1, climbing to 0.3 degrees above Mars on June 18, at their closest pairing. Mercury and Mars remain within 3 degrees June 14-24. Mercury decreases in brightness, from magnitude -1.0 on June 1, through 0.0 on June 16, to +1.0 on June 30. Mercury fades rapidly in first days of July, but in June, it remains much brighter than Mars’ magnitude +1.8—as faint as Mars ever gets.

Elsewhere in the west to northwest, Procyon and Capella drop out of sight, but the Gemini Twins, Pollux and Castor, 4.5 degrees apart, hold on. During June 18-21, first Mercury, then Mars, pass 5.5 degrees south (to the lower left) of Pollux for two nights each, while the Mercury-Mars pair widens from 0.3 to 1.8 degrees apart. Mercury is the brightest member of this gathering of two planets and two stars.

In June, Regulus slides down the western sky on its way to its conjunction with the sun on Aug. 23. Spica and Arcturus pass their highest positions in the south. Golden Arcturus, at magnitude -0.1, is the brightest star on June evenings, but the planet Jupiter, at magnitude -2.6 in the southeast, appears 10 times brighter. Note red, twinkling Antares within 12 degrees to Jupiter’s upper right on June 1, and within 9 degrees to its right at dusk on June 30. Jupiter is at opposition to the sun on June 10, and is retrograding, or appearing to move westward against the background stars.

By mid-June, Altair rises north of east to complete the Summer Triangle with Vega and Deneb, just in time for the new season. Summer begins at 8:54 a.m. on June 21, with the sun directly over the Tropic of Cancer. The highest sun of the year, only 10 degrees south of overhead for Palm Springs, occurs that day at 12:48 p.m.

Saturn rises in time for mid-twilight in the last days of June. Watch for it in the east-southeast, 31 degrees to the lower left of Jupiter. Saturn’s opposition will occur on July 9.

On the morning twilight chart below, you’ll find the stars, but not fast-moving Venus, in roughly the same positions they’ll occupy in evening twilight in November. On June mornings (and November evenings), the Summer Triangle moves west of overhead. Bright Jupiter, with Saturn to its upper left, will be sinking into the southwest. Fomalhaut, Mouth of the Southern Fish, will be low in the south-southeast to south. Capella, the “Mother Goat” star, will be rising in the northeast. Aldebaran, eye of Taurus, rises in the east-northeast late in month. By getting up before dawn, you’ll get a preview of the evening sky of the next season!

Alignments: On May 31, Earth and Aldebaran are on opposite sides of the sun. As seen from Earth, Aldebaran appears in conjunction with the sun, hidden from our view until it emerges in the east-northeast morning twilight in late June. Also on May 31, Earth passes between Antares and the sun, and that star appears at opposition to the sun, visible almost all night.

On June 10, Jupiter will be at opposition, 180 degrees from the sun and visible all night. Jupiter that night is low in the southeast at dusk, and reaches its highest in the south in the middle of the night, and is low in the southwest at dawn. On July 9, Saturn will be at opposition.

For nearly all of June, Mercury has a favorable evening appearance, including a close approach to Mars for several evenings around June 18. In morning twilight on June 1, Venus is very low in the east-northeast, with the old moon nearby. Jupiter is low in the southwest, 150 degrees from Venus, while Saturn is 29 degrees to Jupiter’s upper left. On July 1, the old moon is again near Venus, but Jupiter has already set. Instead, Saturn will be low in the southwest nearly 160 degrees from Venus. In June, the gap between Venus and these giants widens toward 180 degrees, at mutual oppositions reached by Venus-Jupiter on June 23, and Venus-Saturn on July 17.

There are evening pairs of planets at mutual opposition: Mercury (setting) and Jupiter (rising) on May 30; Mars (setting) and Saturn (rising) on June 14; and Mercury (setting) and Saturn (rising) on June 16. Jean Meeus, in his Mathematical Astronomy Morsels IV, wrote about planets in mutual opposition: “Certainly this is a matter of almost zero observational interest. Somebody who likes to observe weird things might be interested in the near-simultaneous rise/set of two planets in opposition, but it’s far from the mainstream.”

Mercury, Mars and the Twins of Gemini: These four objects are visible in the west-northwest at dusk throughout June, but Mercury is very low at start of month, and all are low in the closing days. I already mentioned Mercury’s fading brightness and Mars’ relative faintness. Watch these changing arrangements of Mercury and Mars with Pollux and Castor, the “Twin” stars of Gemini, 4.5 degrees apart. Binoculars enhance the view, especially late in month, when all will be low in bright twilight. June 5: Mars forms an isosceles triangle with Pollux-Castor, 11 degrees from each. June 12: Mercury forms an isosceles triangle with Pollux-Castor, 10-11 degrees from each. June 18: Mercury-Mars appear closest, 0.3 degrees apart, within 6 degrees to the lower left of Pollux. June 18 and 19: Mercury is 5.5 degrees south (to the lower left) of Pollux. June 20 and 21: Mars is 5.5 degrees south of Pollux. June 25: A line from Castor to Pollux, extended 8.7 degrees, locates Mercury. (The three objects appear to be in a straight line.) June 28: A line from Castor to Pollux, extended 7.2 degrees, locates Mars.

The moon on June evenings: On June 4 at dusk, look low in the west-northwest for the young crescent moon with earthshine, with bright Mercury 7 degrees to the lower right, and faint Mars 7 degrees to the upper left. Jupiter rises about one hour before Mercury sets. Try to view Mercury, Mars and Jupiter simultaneously, within an hour after sunset. On June 5, find Mars 7 degrees to the moon’s lower right, and Pollux 8 degrees to moon’s upper right. On June 6, use binoculars to find the Beehive Cluster within 3 degrees to moon’s upper left after nightfall. Find Regulus near the moon on June 8. The moon passes first quarter phase on June 9. Spica is fairly near the moon on June 11 and 12. From June 12 and for the rest of Mercury’s evening apparition, Mercury and Mars are no more than 4 degrees apart. On June 14 at dusk, find Antares 14 degrees to the moon’s lower left. On June 15, find bright Jupiter 8 degrees to the moon’s lower left, and Antares 7 degrees to moon’s lower right. On evening of June 16, the moon is 6 degrees to the lower left of Jupiter. The full moon later that night, at 1:31 a.m. on June 17, is the fourth during spring 2019. On the evening of June 17, the moon, past full, rises 18 degrees lower left of Jupiter.

Follow the moon in morning sky through the latter half of June. On the 16th, the moon, not quite full, sets in the west-southwest shortly before sunrise, 5 degrees to the lower right of Jupiter. On the next morning, June 17, the full moon appears 8 degrees to the upper left of Jupiter and 22 degrees to the lower right of Saturn. On June 18, the moon will have moved more than two-thirds of the way from Jupiter toward Saturn, and on June 19, the moon will appear 4 degrees to the upper left of Saturn. On June 25, the moon will reach last quarter phase, half full in the morning sky. On June 29, a beautiful crescent moon with earthshine will appear low, north of east, accompanied by the Pleiades cluster, 10 degrees to the upper left, and bright Aldebaran, eye of Taurus, 15 degrees to the lower left. On the 30th, a thinner crescent moon will appear with Aldebaran within 2 degrees below.

Abrams Planetarium publishes a monthly Sky Calendar with an evening sky map. The calendar illustrates many of the events described in this article. Subscriptions are $12 per year at www.abramsplanetarium.org/skycalendar for three printed issues mailed quarterly.

Check the website of the Astronomical Society of the Desert at www.astrorx.org for dates and times of our evening star parties.Sawmill Trailhead, our high-altitude site (elevation 4,000 feet), will have its next monthly session starting at dusk on Saturday, June 1.

Wishing you clear skies!

Robert Victor was a staff astronomer at Abrams Planetarium at Michigan State University. He is now retired and enjoys providing sky watching opportunities for a variety of groups in the Coachella Valley. Robert 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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