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Sky and mountains

Photo of the Week.Sky above all....

Astronomy news for the week starting Friday, September 5, 2014.

The Moon begins our week late in its waxing gibbous phase, rocks by full phase on Monday the 8th (about the time of Moonrise in North America), then the rest of the week dims through the early part of its waning gibbous phase. While the coincidence of perigee (when and where the Moon is closest to Earth, the night of Monday the 7th) is not as good as it was at the last full Moon, this "supermoon" (on the average 12 percent larger than an apogean Moon) is almost as good. There are no planetary passages of note, unless we count one well north of Neptune on Monday the 8th and another past Uranus on Wednesday the 10th. The latter is a bit of a curiosity, as the waning gibbous Moon will occult, or pass in front of, the planet as would be seen from the far north (it's not worth a trip to Siberia). With the Sun approaching the autumnal equinox in Virgo, this full Moon will be riding the southern ecliptic not far from the vernal equinox in Pisces, the constellation's dim stars mostly hidden by lunar brightness.

In the evening, though both are near setting by 10 PM Daylight Time, Saturn and Mars are still quite visible as twilight draws to a close. They are widening the gap between them, faster-moving Mars only slowly falling behind the Earth as both orbit the Sun. By the end of the week, the red planet will be roughly halfway between Saturn and Antares in Scorpius, the star slightly the fainter but of similar color to Mars (hence "Ant-Ares" after the Greek god of war). In the morning sky, Jupiter and Venus are separating as well. Though still bright, Venus is a challenge as it rises half an hour after the break of dawn. Jupiter on the other hand is shifting in the other direction, rising earlier, now just after 3:30 AM within the confines of dim Cancer, the planet quite unmistakable as it climbs above the eastern horizon.

The Moon will wash out most of the stars, only the brighter ones shining through. In the northwest, though, the faithful Big Dipper is still seen, all but one of its stars second magnitude. The stellar brightness scale was invented around 130 BC by the Greek astronomer Hipparchus of Nicea, who divided the naked eye stars into six categories, first magnitude the brightest, sixth the faintest. The system, though modified and set on a modern mathematical scale, is still in use today. There are but 22 first magnitude stars, which actually run into magnitude zero and -1 (Venus going to -5!). Each full magnitude is about 2.5 times brighter than the next fainter one. Oddly, the brightest and faintest of the first magnitude set, Sirius and Adhara, are in the same constellation, Canis Major, Orion's larger hunting dog. Both stars are coming onto the scene in late morning skies to the southeast of the Hunter, giving us a preview of winter.

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