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Thursday, 01 August 2013 15:30

August Astronomy: It’s Time to Enjoy the Milky Way

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August Astronomy: It’s Time to Enjoy the Milky Way Robert D. Miller

At dusk, watch Venus slowly close in on Spica and Saturn, until pairings occur in September.

Meanwhile, the best Milky Way viewing occurs this year on evenings through Aug. 9, and then again Aug. 26 through Sept. 7. Get to a dark site by nightfall, and enjoy!

Dark moonless predawn hours of Aug. 12 and 13 make this an excellent year for the annual Perseid meteor shower. And mid-August, dawn brings forth the greatest number of bright stars visible simultaneously.

Venus continues as the brilliant evening “star” low in evening twilight, while drifting from west to west-southwest as month progresses. Valley residents living closely east of mountains (such as near downtown Palm Springs) will want to seek out a location where the mountains don’t block the planet from view.

Venus will grace our evening sky until early January 2014. Until then, a waxing crescent moon passes Venus monthly, producing the most striking views at dusk on Friday, Aug. 9, and on Sunday, Sept. 8. Don’t miss these!

On our evening all-sky chart above, planets are plotted for each day when the sun has sunk to 9 degrees below the horizon, at “mid-twilight.” By then, two naked-eye planets and a half-dozen stars of first magnitude or brighter are easily seen. In mid-August in the Coachella Valley, mid-twilight occurs about 42 minutes after sunset.

Planet positions are represented by a separate dot for each date, with positions for each Thursday in August (1, 8, 15, 22, 29) represented by a larger dot and labeled. We find Saturn and Spica in the southwest to west-southwest sky this month, to the upper left of Venus. Rotate the chart until the portion of the horizon circle nearest to your target objects is below them, and you’ll see them depicted at the same orientation as they appear in the sky: On Aug. 1, Venus is in the west, with Saturn in the southwest 53 degrees to Venus’ upper left, while Spica is 12 degrees to the lower right of Saturn, and 41 degrees to the upper left of Venus. On Aug. 31, Venus is in the west-southwest, with Saturn 19 degrees to its upper left, while Spica is just 6 degrees to the upper left of Venus, and 14 degrees to the lower right of Saturn.

On the chart, stars’ daily positions are plotted not as individual dots, but instead by continuous tracks as the stars drift west (counter-clockwise around the North Star) over the course of the month, owing to the Earth’s revolution around the sun.

The brightest star in August’s evening sky is golden Arcturus, high in the west-southwest to west, to upper right of Saturn and Spica and forming a large triangle with them. When the sky darkens enough for the Big Dipper to become visible, you can “follow the arc (of the handle) to Arcturus and drive a spike to Spica.”

A close second to Arcturus in brilliance is blue-white Vega, very high in the east-northeast. Compare the contrasting colors of these two stars! To Vega’s lower left is Deneb, and to Vega’s lower right is Altair, completing the Summer Triangle. Face south to south-southwest to find reddish Antares, heart of the Scorpion.

From Aug. 8-21, the moon is above the horizon in evening mid-twilight. Follow it nightly as it waxes, or grows, from a thin crescent on Aug. 8, past first quarter (half full) by Aug. 14, to full on Aug. 20. The moon appears near Venus on Aug. 9, Spica on the 11th, Saturn on the 12th, and Antares on the 15th.

(I recommend the Abrams Planetarium Sky Calendar for its easy-to-follow illustrations of the changing positions of moon and planets against background stars. The current issues feature illustrations of the changing arrangements of Venus-Spica-Saturn at dusk and Jupiter-Mars-Mercury at dawn. Each month, an all-sky evening chart of the constellations is also provided. To subscribe, visit www.pa.msu.edu/abrams/SkyCalendar.)

Star Parties

The Astronomical Society of the Desert hosts free public sky-watching sessions at Sawmill Trailhead on Saturday evenings, Aug. 3, and Sept. 7. For more information and directions, visit www.astrorx.org and www.astrorx.org/sawmill%20Directions.htm.

August Evening Moonrise Watch

The full moon occurs on Tuesday, Aug. 20, at 6:45 p.m. in the Coachella Valley.

That evening, the moon rises nine degrees south of east at 7:05 p.m., about 22 minutes before sunset. Does the full moon at rising seem large? The moon at rising or setting always seems large (the “moon illusion”), even when it is at its most distant from Earth.

For those who enjoy watching or photographing the moon’s big reddened disk coming up over distant mountains, here are moonrise times for the Coachella Valley until a week after full. Times are when the moon’s disk would just start to appear over an ideal, flat horizon. In practice, our mountainous surroundings will delay risings and hasten settings by several minutes.

Tuesday, Aug. 20: 7:05 p.m.—9 degrees south of east (full)

Wednesday, Aug. 21: 7:44 p.m.—3 degrees south of east (98 percent)

Thursday, Aug. 22: 8:21 p.m.—3 degrees north of east (94percent)

Friday, Aug. 23: 8:57 p.m.—8 degrees north of east (88 percent)

Saturday, Aug. 24: 9:34 p.m.—13 degrees north of east (80 percent)

Sunday, Aug. 25: 10:12 p.m.—17 degrees north of east (71 percent)

Monday, Aug. 26: 10:53 p.m.—21 degrees north of east (61 percent)

Tuesday, Aug. 27: 11:35 p.m.—23 degrees north of east (51 percent)

August Predawn Riches!

Up to 13 objects of first magnitude or brighter, and a meteor shower, are all visible in the early morning hours! Our all-sky chart for morning mid-twilight, below, depicts the sky about 42 minutes before sunrise in the Coachella Valley.

Jupiter is the bright morning “star.” In mid-twilight, you’ll find it about 20 degrees up in east-northeast on Aug. 1, and climbing nearly halfway from the east horizon to overhead by month’s end. Mars, of magnitude 1.6 (and not quite qualifying as first magnitude), is to the lower left of Jupiter, within 5 degrees on Aug. 1, and widening to 18 degrees by Aug. 31. Mercury on Aug. 1 is within 8 degrees to the lower left of Mars and 12 degrees to the lower left of Jupiter, but drops into bright twilight around mid-month. To Jupiter’s upper left, find bright Capella, the “Mother Goat” star, in the northeast, getting higher as month progresses. To the upper right of Jupiter is reddish Aldebaran, eye of Taurus the Bull, with the compact Pleiades star cluster or Seven Sisters (not shown), 14 degrees higher. Below Taurus, find Betelgeuse and Rigel, shoulder and foot of Orion the Hunter (with his belt, a nearly vertical line of three stars midway between them, not plotted).

The Summer Triangle of Vega-Deneb-Altair is still visible in the west to west-northwest at dawn early in August, but only Deneb remains at month’s end.

From midnight through the predawn darkness hours of Monday and Tuesday, Aug. 12 and 13, watch the annual Perseid meteor shower rise to peak. With no moon present to spoil the view, this is a very good year!

After viewing the shower, follow Orion’s belt downward as dawn brightens to watch for the rising of Sirius, the “Dog Star,” in the east-southeast. Procyon will have already risen in the east; it completes the Winter Triangle with Sirius and Betelgeuse. Try to spot Sirius before you lose sight of Altair sinking in the west, and you’ll see both the winter and summer triangles simultaneously!

If you succeed, you can tally 11 stars and two planets of first magnitude or brighter. We’ve not yet mentioned Pollux, in the east-northeast to the lower left of Jupiter (with 1.6-magnitude Castor, the other Gemini Twin, not plotted, 4 1/2 degrees above Pollux), and Fomalhaut, mouth of the Southern Fish, very low in southwest.

The waning crescent moon in the morning sky appears near the Pleiades star cluster on and Aug. 27, Aldebaran on Aug. 1 and 28, Jupiter on Aug. 3 and 31, Mars on Aug. 4 and Sept. 2, and Mercury on Aug. 5.

Robert C. Victor was a staff astronomer at the 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 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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