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Wed08202014

Last updateSat, 11 Jan 2014 11am

Astronomy

The full moon occurs on Sunday, Aug. 10, at 11:09 a.m. The moon passes perigee—221,765 miles from Earth, the closest approach of the year—at the same hour.

But this “supermoon,” visible at dawn and dusk on that date, is not the brightest moon of 2014, because of the phase effect, which makes the moon’s brightness decrease sharply when it’s a few degrees away from being exactly 180 degrees from the sun. You can duplicate this effect one night by standing between a stationary bright-light source and a highly reflective road sign, so that the shadow of your head is cast upon the sign. Note how the sign really lights up around your head’s shadow, giving the shadow a brilliant “halo.” However, if you take a step or two to left or right, you’ll notice how quickly the road sign fades away.

August's full moon passes four to five degrees north of Earth’s shadow center, causing the moon to set after sunrise and rise before sunset on Aug. 10. Further, the timing of the full moon, during the daytime, places the moon widely northwest of the Earth’s shadow at sunrise, and northeast of it at sunset.

Even with the moon not as bright as could be, there are no truly dark skies between dawn’s first light on Aug. 8 and nightfall on Aug. 14. This fact will largely spoil this year’s Perseid meteor shower, which would otherwise be at its best in the predawn darkness hours of Wednesday, Aug. 13.

If you’re outdoors that morning as twilight brightens, watch for Jupiter rising in the east-northeast, 5 degrees to the lower left of Venus. Venus goes east against background stars by 1.2 degrees per day compared to Jupiter’s 0.2 degrees; watch their separation narrow by about 1 degree daily.

Don’t miss the spectacular pairing of Venus and Jupiter on Monday, Aug. 18, within 0.4 degrees. Five days later, on Saturday, Aug. 23, the old crescent moon joins the brilliant planets in a beautiful scene.

Evening planets: Find the planets Mars and Saturn in the southwest at nightfall, and compare them in brightness and color to each other; to bluish Spica, to their lower right; and to reddish Antares, to Saturn’s left. The stars will twinkle noticeably.

Watch the Mars-Saturn gap shrink until they’re 3.4 degrees apart on Aug. 25, and then widen to 5.0 degrees apart by Aug. 31. The moon will appear near these planets on Aug. 31.

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.