Fast-moving Mars and Venus make eye-catching arrangements with Pollux and Castor this month, before the twin stars’ annual departure into the evening twilight glow. Even the slow motions of Jupiter and Saturn can be noted with careful attention to background stars.
The moon pairs up with four of the five naked-eye planets and four of the five zodiacal first-magnitude stars. Venus presents its northernmost setting of 2021 on June 4, 16 days before the sun does so. The aptly named Summer Triangle is visible from dusk until dawn from late June until early August.
In June’s evening twilight: The only planets visible at dusk are bright Venus, of magnitude -3.8, very low in the west-northwest, and faint Mars, of magnitude +1.8, some 25 to 7 degrees to Venus’ upper left. The brightest stars visible, both of zero magnitude, are golden Arcturus, very high in the southeast to south-southwest, and blue-white Vega, climbing high in the east-northeast.
In early June, the Spring Arch of four stars is still visible: Procyon, low in the west; twins Pollux and Castor, atop the arch and 4.5 degrees apart in the west-northwest; and Capella, low in the northwest. The twins remain visible at month’s end, but only with the aid of binoculars.
Watch for these striking arrangements of planets with twin stars Pollux and Castor: Mars, on June 7, is 7 degrees to the left of Pollux and forms a straight line with the twins. Venus, on June 13, forms an isosceles triangle with the twins. On June 21, Venus passes 5.2 degrees to the south (lower left) of Pollux, its least distance from that star. On June 24, Venus is 6.5 degrees to the left of Pollux and forms a straight line with the twins.
Other stars visible at dusk: Regulus, heart of Leo, is in the west-southwest to west, to the upper left of Venus and Mars. (Mars closes to within 18 degrees of the lower right of Regulus at month’s end.) Spica, the spike of grain in the hand of Virgo, crosses through south into south-southwest, 33 degrees to the lower right of or below Arcturus. Antares, heart of the Scorpion, starts very low in the southeast and climbs into the south-southeast. Look for Deneb to the lower left of Vega. Watch the horizon a little more than 10 degrees north of east, to Vega’s lower right, for the rising of Altair, completing the Summer Triangle with Vega and Deneb.
Follow the moon for two weeks as it waxes from a thin crescent on June 11 to full on June 24. Watch for its pairings with planets and bright zodiacal stars on the evenings of June 11 (Venus); 12 (Pollux); 13 (Mars); 15 (Regulus); 19 (Spica); and 22 (Antares).
All these events are illustrated on the Sky Calendar for June 2021. To subscribe for $12 per year (for three printed monthly issues mailed quarterly), or to view a sample issue, visit www.abramsplanetarium.org/skycalendar.
At end of June, Saturn rises in the east-southeast within two hours after sunset, and brighter Jupiter rises within an hour later, nearly 20 degrees to the lower left of Saturn.
In coming months, watch for changes in setting place of the “evening star.” Venus, at magnitude -3.8, sets in the west-northwest between 1.4 and 1.7 hours after sunset this month. On June 4, Venus attains a declination of +24 degrees, 26 minutes north of the Earth’s equator, and sets farthest north, 30 degrees north of west (as seen from our latitude, 34 degrees north). After little change for nearly two weeks, you’ll notice the start of a dramatic swing in Venus’ setting place during this apparition, to a declination of -27 degrees, 15 minutes, on Nov. 6. Venus will then set 33 degrees south of west—a southward shift in azimuth of 63 degrees in five months!
On June 17 and 18, Venus follows the sun down to the horizon, on same arc, but trailing sun by 96 minutes.
The summer solstice, “sun standstill,” occurs on June 20, as the sun reaches its northernmost position, directly over the Tropic of Cancer, at 8:32 p.m. Earlier that day in Palm Springs, our highest sun of the year passes just 10.4 degrees south of overhead at 12:48 p.m.
In June’s morning twilight: Look to the southern sky at dawn to see Jupiter, of magnitude -2.4 to -2.6, the brightest morning “star,” and Saturn, three magnitudes fainter at +0.6 to +0.4, between 18 and 20 degrees to Jupiter’s right or lower right. Watch these planets move! Use binoculars before twilight begins to view the fourth-magnitude star Iota in Aquarius, about 3 degrees from Jupiter all month. Jupiter begins to retrograde on June 20, and will go 10 degrees west in the next four months, ending on Oct. 17. Jupiter will pass about 1 degree from Iota on Aug. 6 and Dec. 20, completing a triple conjunction with that star. Binoculars will also show fourth-magnitude Theta in Capricornus, 0.7-1.7 degrees west-southwest of Saturn this month. Saturn’s retrograde of nearly 7 degrees, which started on May 23, will continue until Oct. 10, when the ringed planet will be 7.3 degrees west-southwest of Theta.
Antares makes its exit in the southwest in June’s morning mid-twilight sky, and Arcturus departs in the west-northwest, both in the second week. (By end of June, they set more than two hours before sunup.) TheSummer Triangleof Vega, Altair and Deneb passes west of overhead, while Fomalhaut,mouth of the Southern Fish, glows low in the southeast to south, 20 degrees below or to the lower left of Jupiter.
Capella appears very low in the north-northeast at the start of June, and rises higher into the northeast as the month progresses. Late in June, look for Aldebaran, eye of Taurus, the Bull, very low in the east-northeast, 31 degrees to the lower right of Capella. On June’s last two mornings, use binoculars to spot first-magnitude Mercury rising 8 degrees to the lower left of Aldebaran. Mercury will brighten further and be easier to spot during the first three weeks of July.
Watch the waning gibbous moon pass Saturn and Jupiter on the mornings of May 31 and June 1, and on June 27-29. In June’s morning twilight, the waning moon can be followed during the first and last weeks of month, June 1-7 and 24-30.
The solar eclipse of June 10 can NOTbe seen from California. An annular, or “ring of fire,” eclipse will occur within a path through Canada and the arctic, while parts of the eastern and north-central U.S. will see a partial eclipse near sunrise. Coachella Valley’s next chances to view a solar eclipse will come on Oct. 14, 2023, and Apr. 8, 2024.
Robert Victor was a staff astronomer at Abrams Planetarium at Michigan State University. When the coast is clear, he looks forward to sky-watching sessions, in time for a fine display of three planets in the evening sky in autumn 2021. 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.