Summer Planet Watch
Riddle, Bob, Science Scope
Byline: Bob Riddle
Figure 1. Mercury, the Gemini twins, Mars, and Saturn on June 17 at 9:45 p.m. EDT
This summer, all but one of the bright planets will be easily visible as evening planets during the first part of our Northern Hemisphere summer season, and then shift to the predawn skies during the latter half of summer. The one constant, with regard to evening visibility, will be the planet Jupiter. Located inside the western boundary of Libra, the Scales, Jupiter will be easily seen over the western horizon at sunset approximately 15 degrees east of the blue-white star Spica in the constellation Virgo. By the end of August, Jupiter will have moved about 20 degrees further east within the boundaries of the constellation of Libra.
The remaining visible planets, Mercury, Venus, Mars, and Saturn, on the other hand, will go through more observable changes in their relative positions as the days of summer pass by.
Venus will be the sole morning planet until joined by Mercury during August. If you had followed the path
Figure 2. Mars, Saturn, and M-44 as seen through 7 x 50 binoculars on June 17.
Mars took across Aries and Taurus this past year, then the location and motion of Venus will look familiar. In June, Venus will move eastward away from the stars of Aries, the Ram, and will cross into the region of Taurus, the Bull, as it passes the open star clusters, the Pleiades and Hyades, during the latter half of the month. During July and August, Venus will move below the stars of the pentagon-shaped constellation of Auriga, the Charioteer, past the feet of the Gemini twins and eventually reach a planetary rendezvous, of sorts, with Mercury on August 21, east of the Gemini twin stars Pollux and Castor.
The evening action will be almost all during June and the first half of July as Mercury, Mars, and Saturn will rearrange themselves near the bright Pollux and Castor, and the bright star Regulus in Leo, the Lion.
During June, Mercury will appear over the western horizon at sunset and will quickly rise higher each evening (it will be seen setting a few minutes later each evening). Mercury will begin this evening apparition at the feet of the Gemini twins, and will end its visibility at month's end lined up with and just to the left of Pollux and Castor (see Figure 1).
Mars and Saturn will play a game of planetary tag as the faster-moving Mars will move eastward, catching up with and passing Saturn. Saturn will continue moving eastward, away from the Beehive Cluster, M-44, an open star cluster just barely visible to the unaided eye in dark skies. On the other hand, or actually orbit, Mars will start June lined up with Pollux and Castor at about where Mercury will be at the end of June. The Red Planet will quickly move to within about one-half degree of Saturn on June 17, after having passed across the center of the Beehive Cluster a few days earlier (June 14-16). These two planets and M-44 should make for an interesting view with binoculars or a wide-field telescope eyepiece (see Figure 2). By the end of June, only Mars will be left, very low over the western horizon. On July 21-22, Mars will very closely pass Regulus in Leo. However, the pair will be very low over the western horizon and may not easily be seen. By the end of July, only Jupiter will remain as an evening planet, and it too will slip below the western horizon and no longer be seen by the end of August. …