Venus and Jupiter in the west are closing toward a spectacular close pairing on June 30, while Saturn climbs in the southeast in the early evening. These three naked-eye planets, all showpieces for telescopic observation, should make a star party in June an exciting affair—so we hope you can arrange to attend one!
Evenings: Venus and Jupiter are easy to spot until late July 2015, because they far outshine all nighttime stars.
In June and July, Venus sinks lower in the evening sky while increasing in brightness and getting ever more interesting for telescopic observation: On June 6, Venus reaches greatest elongation, 45 degrees to the upper left of the setting sun; as seen through a telescope around that date, the planet appears as a tiny “half moon.” In the next 10 weeks, as Venus draws closer to Earth, it displays an ever thinner, more backlit crescent.
Jupiter appears close to Venus in June and July, during the final weeks of their joint appearance in the evening sky. First, Jupiter appears to the upper left of Venus, within 20 degrees on June 1, narrowing to 10 degrees on June 14. From June 22 through July 13, Venus and Jupiter will appear no more than 5 degrees apart, both easily fitting together within the field of view of binoculars magnifying no more than about 10-power.
Venus and Jupiter will form a spectacular close pair on June 30, just 0.3 degrees apart. A telescopic view of the planet pair that evening will be a memorable sight, not to be missed: Venus as a brilliant crescent, one-third full, matching the dim, fully lit disk of Jupiter in apparent size! This coincidence occurs because Jupiter, with a diameter 12 times that of Venus, will then be 12 times as far away! On five consecutive evenings, June 28-July 2, the planet duo will be no more than 1.2 degrees apart, easily fitting within a telescope’s low-power field.
The crescent phase of Venus can be resolved with just a pair of binoculars, by avoiding the planet’s glare against a darkened sky: One of the best occasions in 2015 is in the late afternoon or around sunset, from mid-June until late July/early August.
Saturn, at opposition to the sun on May 22 as the Earth overtook that planet, was visible all night. In the months following opposition, Saturn will remain in the evening sky, reaching its high point in the south about a half-hour earlier each week until crossing due south at dusk in July.
The moon can be followed as it waxes from a thin crescent, through first quarter phase (half full and 90 degrees east of the sun), to full, and about a day beyond—through June 3; and June 18-July 2. Folks new to sky-watching may enjoy keeping a diary or logbook of their observations of the sky, recording the date, time, observer’s location, direction in which the objects were seen, and comments.
Note the final gatherings of the moon with Venus and Jupiter in the evening sky will occur at dusk on June 19-20, and again on July 18, when the moon will appear very close to Venus! On June 17, 30 minutes after sunset from Southern California, a thin moon is about 4 degrees up in the west-northwest, 27 degrees to the lower right of Venus. On June 18, one hour after sunset, get a first easy view of the young crescent moon, 16 degrees to the lower right of Venus and 13 degrees to the lower left of Pollux. Jupiter is just more than 7 degrees to the upper left of Venus. On June 19, the moon is 7 degrees below and a little left of Venus; Jupiter is 6.5 degrees to the upper left of Venus. On June 20, the moon is within 6 degrees of the lower left of Jupiter. Venus is within 6 degrees of the lower right of Jupiter. On June 21, Regulus is 6 degrees to the right of the moon. On June 23, the moon, approaching first quarter phase, is just more than halfway from Regulus toward Spica. On June 25, Spica is 3 degrees to the lower left of the waxing gibbous moon. On June 28, Saturn is just 2 degrees to the right of the moon; Antares is 13 degrees to the lower left of Saturn. On June 29, Antares is 9 degrees to the lower right of the moon. On June 30, don’t miss the spectacular conjunction of Venus and Jupiter, just 0.3 degrees apart.
By the way: Events of this kind are illustrated on the Abrams Planetarium Sky Calendar. Subscriptions are appreciated; get details at www.pa.msu.edu/abrams/skycalendar.
Another enjoyable pastime is to watch the western sky within an hour after sunset to try to follow the planets and bright stars until their latest possible dates. By the end of May, Rigel, Aldebaran, Sirius, and Betelgeuse had already disappeared into the western evening twilight glow. In early June, Procyon sinks from view, and later in June or in earliest days of July (depending on the observer’s latitude), Capella, Pollux and Castor depart. All these disappearances of stars occur annually, at the same times of the year,as a result of the Earth’s revolution around the sun.
Mornings: During the summer and fall of 2015, mornings will also be very interesting for sky-watchers. Those who check the eastern sky regularly about an hour before sunrise can watch for the first appearances of planets and first-magnitude stars. Aldebaran, follower of the Pleiades and rising 14 degrees below that pretty star cluster, will return by the end of June; Betelgeuse, Rigel, Pollux, Castor and Mars do so before the end of July; Procyon and Sirius appear by mid-August; Venus before the end of August; Regulus and Jupiter before mid-September; and Spica by the end of October.
Robert C. Victor was a staff astronomer at Abrams Planetarium at Michigan State University. He is now retired and enjoys providing skywatching opportunities for school children in and around Palm Springs. Robert D. Miller, who provided the twilight charts and the planet orbit 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.