Skylights featured on Astronomy Picture of the Day

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Skylights featured nine times on Earth Science Picture of the Day: 1 2 3 4 5 6 7 8 9

Summer Triangle

Photo of the Week. The Summer Triangle rises against light-polluted skies, Vega of Lyra at the top, Deneb (Cygnus) down and to the left, Altair (Aquila) down toward the far right corner. Compare with the sight from a dark location to see what we have lost.

Astronomy news for the week starting Friday, August 13, 2010.

The Moon begins our week well along in its waxing crescent phase, then passes first quarter around the time of its daytime rising on Monday the 16th. By the time the Sun sets, it will be very slightly past the phase as it launches itself into the waxing gibbous, which will occupy the rest of the week. The evening of Friday the 13th finds our lunar companion nicely to the left of the gang of three, Venus, Mars, and Saturn, with Venus by far the most obvious. A closer look reveals the star Spica up and to the left of the crescent.

Beyond the Moon, the three evening planets continue their intricate western dance, forming a nice triangle, with Mars to the east of Venus as the week begins, Saturn to the north. Faster moving Venus is approaching the red planet as the two near conjunction (which takes place next week). All three now set just before twilight ends, around 9:30 PM Daylight Time, so only brilliant Venus, which by far tops the others, is readily visible.

On Thursday the 19th, Venus passes greatest eastern elongation 46 degrees to the east of the Sun. The configuration usually is at least close to Venus's easiest visibility, but this year it is defeated by the increasing flatness of the evening ecliptic to the horizon, Venus actually at her best a couple months ago. Though setting notably earlier with time, Venus still brightens, and will continue to do so until late September.

As has been the case for some time now, as the evening planets set in the west, Jupiter rises nearly due east, still among the stars of western Pisces just a bit to the southeast of the Vernal Equinox. Look for it later in the evening and to the south as it crosses the meridian around 3:30 AM. Uranus, just to the west of Jupiter, is an even better marker, falling less than a degree south of the Equinox. At sixth magnitude, though, it's a tough sight without optical aid. Even fainter of course, and generally ignored, is Neptune. Almost exactly on the Capricornus-Aquarius border, it makes its own news by passing opposition to the Sun on Friday the 20th, just six hours after Venus goes through greatest elongation.

As July turned to August, we also passed obscure " Lammas Day," a harvest festival that also celebrates the halfway point between the first day of summer and that of fall. One of the four "cross-quarter days," it is to autumn as North America's Groundhog Day is to spring, May Day is to summer, and Halloween is to winter. Which means of course that the summer constellations are slowly moving out to be replaced by those of fall. But we still have a way to go. Look for bright Vega nearly overhead now in mid-evening. Due south and not that far above the horizon lies Sagittarius with its Little Milk Dipper, with Scorpius to the west, far dimmer Capricornus to the east.
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