Jupiter joins Venus in the early evening
A pair of dazzling planets appears side by side as the calendar turns from June to July.
Look to the western sky less than an hour after sunset, and you won’t be able to miss two bright points of light more than a fourth of the way above the horizon. That more brilliant one is Venus, and it’s currently having its best showing for northern observers of 2015 as it shines brightest and appears highest in the evening sky. And right now, it's joined by Jupiter for the first and closest conjunction in a rare set of three.
Venus crosses into Leo the Lion on June 25. The separation between it and magnitude Jupiter has now shrunk to 3°, and the brilliant planets look like a pair of cat’s eyes catching a car’s headlights in the dark. The gap keeps closing over the next five nights, reaching a minimum of just 20' (two-thirds of the Full Moon’s diameter) on the 30th. Both planets will appear in a single field of view through a telescope at low power, and they'll both sport 32"-diameter disks, though Venus' will only be 34 percent lit. But the two planets' similar sizes in the eyepiece don't reflect physical reality — Jupiter's diameter is some 12 times that of Venus, but it also lies 12 times farther away.
On July 1, the dazzling planets stand side by side in the west, still with just a Full Moon’s width between them. Venus shines at magnitude –4.6 and Jupiter at magnitude –1.8. Only the Full Moon itself — climbing higher in the southeastern sky this evening — appears brighter.
As twilight descends, the two planets seem to grow more brilliant in contrast with the darker sky. They hover 8° to the lower right of 1st-magnitude Regulus, Leo the Lion’s brightest star, which forms the base of Leo’s Sickle asterism.
The planet pair remains visible for about two hours after the Sun sets in early July. During the next few weeks, Venus moves southwest (left as seen from mid-northern latitudes) of its companion. By the 9th, 4° separate the two. Venus then shines at magnitude –4.7, the peak brightness for its current evening reign.
The two planets and Regulus create an ever-changing triangle during July. On the 18th, a slender crescent Moon joins the scene to create a perfect picture opportunity. All four objects lie within a 6° circle, with our satellite less than 1° from Venus. And on the 23rd, both Venus and Jupiter appear 4° from Regulus. The trio sinks into bright twilight by the end of July, setting within an hour of the Sun.