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Circumhorizontal arc

Photo of the Week. A fine circumhorizontal arc, caused by sunlight refracting through ice crystals, courses across the sky south of the Sun.

Astronomy news for the week starting Friday, August 15, 2008.

We begin the week with the Moon near the end of its waxing gibbous phase as it approaches full on Saturday the 16th. With the Sun descending the ecliptic from the Summer Solstice, our full Moons are now riding upward from the Winter Solstice, this one -- the "Green Corn Moon," the "Grain Moon" - - lies between classical Capricornus and Aquarius just to the northeast of Neptune, which passes opposition to the Sun as our week begins, on Friday the 15th. Having just had an eclipse of the Sun on August 1, this full Moon will be eclipsed, though just partially and seen in Europe and Asia, the event not visible in North America. The remainder of the week then sees our companion in the waning gibbous phase. On Monday the 18th, it passes a few degrees south of Uranus.

Some nice planetary action takes place nearly invisibly in western twilight, as Saturn, Venus, and Mercury gather together. On Friday the 22nd, Mercury and Venus pass conjunction just 1.2 degrees apart, the event unfortunately not visible without special equipment. At least we know it is happening.

So once again, for planetary viewing we turn to lonely Jupiter, which now dominates the southern sky at the end of twilight, the giant planet now crossing the meridian due south (for those of us in the northern hemisphere) around 10 PM. Setting ever earlier, Jupiter now goes down around 3 AM, leaving us planet-less but for Uranus and Neptune, Uranus transiting just as Jupiter sets.

Mid-August in mid-evening finds the Scorpius-Sagittarius pair (Sagittarius to the east, Scorpius to the west) crossing the meridian to the far south. Due north of Sagittarius, white Vega shines nearly overhead in Lyra, while Arcturus sparkles orange-ly to the west. Sagittarius is now easily located by looking down and a bit to the right of Jupiter, though a bright Moon will blot much of it out. Atop Scorpius, once the Moon is out of the way, look upward to Ophiuchus (the Serpent Bearer), then to Hercules, then to the head of Draco, the Dragon.
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