Friday July 31, 2015; 06:44 am EDT
Sky Watch-Twilight’s Alignment
This week, the west is best
The sun this week passes a psychological yardstick, setting at 8:30 Friday and then a little less than a minute earlier each night. The sun’s exit, stage right, is the parting of the night’s curtain, revealing a stage full of luminaries.
The waxing moon reveals a shadow of itself even in the glare of twilight, high in the southwest at week’s end. Thursday it shines just a few degrees below Mars and 10 degrees to the right of golden Saturn. Venus, unmistakably brilliant, hovers less than 20 degrees to the right of the moon.
Friday night the moon appears farther west, 10 degrees below Saturn, with the blue Spica 20 degrees to the left. Saturday the moon is a half-dozen degrees below Spica. Sunday’s first-quarter moon shines between the constellation Virgo to the right and Libra to the left.
Monday the moon travels amid the scales of Libra. At magnitude 2.6, the constellation’s brightest star is the nondescript blue-white Zubeneschamali, 14 degrees above the moon. Slightly dimmer at magnitude 2.75, the constellation’s second-brightest star, Zubenelgenubi, is six degrees above the moon. The fulcrum of the scales, Zubenelgenubi is the only green star visible to the unaided eye.
Tuesday and Wednesday the moon is to one side of Antares and then the other. While the moon moves eastward over the course of the week, the western sky hosts the action, with six bright objects stretched in a loose line from low in the west to the south.
Visually, Venus holds center stage, appearing in the southeast amid the glow of twilight. A few degrees to the west is Regulus, the heart of Leo the Lion. Even closer to the western horizon is the elusive planet Mercury, which sets within an hour of the sun.
To the east of Venus is Mars, followed by Saturn, with Regulus far to the south. This week, Mars and Saturn pull within a few degrees of one another, with Venus joining the frey at month’s end.