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Last updateWed, 27 Aug 2014 10am

Astronomy

Jupiter sets almost an hour after the sun on Aug. 1, and three minutes earlier each evening thereafter. Using binoculars a half-hour after sunset, look very low, about midway between west and west-northwest, to the left of the sunset point.

If you can still find Jupiter on Aug. 5, try for Mercury, 1.9 degrees to its lower right. On Aug. 6, Mercury is 0.6 degrees to the upper right of Jupiter, and on Aug. 7, it is 1.4 degrees to Jupiter’s upper left. The solar system’s largest planet will be hidden for several weeks while it passes conjunction on the far side of the sun on Aug. 26. Meanwhile, Mercury makes a very low evening appearance, 4 degrees above the western horizon in mid-twilight (about 40 minutes after sunset) from Aug. 18 to Sept. 4, staying at magnitude 0 while shifting from 3 degrees north of west to 10 degrees south of west. Jupiter will emerge into the morning sky in September, joining Venus and Mars to form a spectacular compact trioin late October.

Venus passes inferior conjunction, nearly between Earth and the sun, 8 degrees south of the sun’s disk, on Aug. 15. On the morning of Aug. 17, Venus rises 8 degrees to the right of the sun, simultaneously with it. On Aug. 21, Venus rises 30 minutes ahead of the sun; on Aug. 26, just more than an hour before sunup; and by Aug. 30, Venus rises spectacularly in a dark sky 90 minutes before the sun.

Use binoculars or a telescope to observe its thin crescent phase, while avoiding the planet’s glare against a dark sky. Once you start seeing Venus in the morning sky in late August, just keep track of it until sunrise, and you’ll have a daytime sighting of Venus! This “morning star” will be most interesting through binoculars and telescopes from late August through late October.

If you enjoy the simple pleasure of watching the moonrise over a distant landscape, here’s when to look from the mid-Coachella Valley: On July 31, the full moon rises at 7:59 p.m., less than a quarter-hour after sunset. On Aug. 1, moonrise occurs at 8:44 p.m., within an hour after sunset. On Aug. 2, the moon rises at 9:26 p.m., just after the end of twilight. For the next few days, the moon rises about 40 minutes later each evening. By Aug. 4, the moon comes up at 10:47 p.m., three hours after sunset, allowing a nice window of dark skies before moonrise for enjoying the summer Milky Way. Note the summer triangle of Vega, Altair and Deneb plotted on August’s twilight sky charts. On moonless nights, look near the center of the summer triangle for the Cygnus Star Cloud—a bright patch of the Milky Way, containing stars within our own spiral arm. On dark nights, binoculars easily resolve the Cygnus Star Cloud into stars.

Returning to the sky in evening mid-twilight, we notice that Venus, so prominent in July, is absent; Jupiter is present only early in the month; and Mercury hugs the western horizon after Jupiter has departed. That leaves Saturn as the brightest object less than halfway to overhead. Find it in the south-southwest to southwest at dusk, with reddish twinkling Antares, heart of the Scorpion, 13 degrees to its lower left in all of August.

The rings of Saturnare now tipped 24 degrees from edge on. On evenings in August, Earth is in position to allow our best view of the shadow of the planet cast on the rings, giving the scene a beautiful 3-D appearance. Telescopic views are impressive! View Saturn and many deep-sky objects on Saturday, Aug. 15, at the Astronomical Society of the Desert “star party” at Sawmill Trailhead. For additional information, directions and a map, visit www.astrorx.org.

Golden Arcturus, high in the western sky, and blue-white Vega, high in the northeast, both outshine Saturn. Look also for Spica in the southwest, to the lower left of Arcturus and west (lower right) of Saturn.

The moon can be followed in evening twilight daily, Aug. 16-29, as it waxes from a thin crescent, through first quarter phase (half full and 90 degrees east of the sun on Aug. 22), to full.

Mornings during the summer and fall of 2015 will be fascinating for sky watchers. Those who check the eastern sky regularly about an hour before sunrise can watch for the first appearances—called heliacal risings—of planets and first-magnitude stars. Procyon and Sirius will appear by mid-August; Venus before the end of August; Regulus and Jupiter before mid-September; and Arcturus and Spica by the end of October.

This is a great year for the Perseid meteor shower. The peak—in dark skies on the night of Aug. 12-13—nearly coincides with the new moon. Best viewing is from late evening until the first light of dawn. Meteors belonging to this stream could appear anywhere in the sky, since the stream is much wider than planet Earth. However, if you extend the meteors’ trails backward beyond where they light up in the Earth’s atmosphere, they will all streak away from a point in the constellation Perseus, below the “W” of Cassiopeia in the northeastern sky. As evening twilight ends, this radiant point is very low in the sky, resulting in meteors making long trails through Earth’s atmosphere nearly parallel to the ground. During the night, as the Earth rotates, the radiant climbs ever higher in the sky, and our part of the Earth turns more nearly broadside to the incoming meteors. So the count of meteors is expected to be highest just before the start of morning twilight on Thursday, Aug. 13.

Another peak of activity might be seen on the previous morning, Wednesday, Aug. 12. That’s because before noon that day, the Earth passes nearest to a trail of dust left by Comet Swift-Tuttle in 1862. (That comet is the source of material for the Perseid meteors.) If the stream is broad enough, we could see enhanced numbers of meteors on Wednesday morning, too.

Resource: Get a sample issue and subscribe online to the Sky Calendar at www.abramsplanetarium.org/skycalendar.

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.

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