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Purple flowers

Photo of the Week. Purple flowers frame a blue sky.

Astronomy news for the week starting Friday, September 23, 2011.

During the early part of the week, the morning skies are ruled by the slim waning crescent Moon. The morning of Saturday the 24th, find it rising well below Mars, then the morning of Sunday the 25th even lower and down and to the right of rising Regulus of Leo. Unless you are especially diligent, that will be your last lunar look before the new Moon of Tuesday the 27th. But then, having passed by the Sun, the Moon pops up as a thin waxing crescent the evening of Wednesday the 28th, then grows as it heads toward first quarter next week. Just half a day after the new phase, the Moon passes perigee, where it is some six percent closer to us than average, the timing leading to especially high and low tides at the coasts.

Jupiter makes something of a transition this week as it rises around 8:30 PM just as evening twilight comes to a close. Passing the meridian around 3 AM, by the time dawn commences the giant planet is well into the west, its location midway between the flat triangle that makes the classical figure of Aries and the ragged circle that represents the head of Cetus, the Whale. To the east of Jupiter, Mars begins to climb the sky around 2 AM, an hour or so before Jupiter transits. Now well into Cancer, the red planet is heading easterly toward the Beehive Cluster. Finally, the sky is bracketed this week by the innermost planet and by the most outerly one that is visible to the naked eye. On Sunday the 25th, Uranus stands in opposition to the Sun (rising at sunset, setting at sunrise, crossing the meridian at midnight), while on Wednesday the 28th, Mercury passes superior conjunction with the Sun (on the other side of it).

By the time the Sun comes up on Friday the 23rd, it will just barely have passed the Autumnal Equinox in Virgo and fall will have begun in the northern hemisphere. On this day we thus have just over 12 hours of daylight and the Sun will set nearly due west. Watch as the points of sunrise and sunset creep toward the south of east and west as autumn deepens toward winter.

Scorpius, Sagittarius, and the rest of the southern-sky summer gang now slip off to the west. But memories of summer still last through the Summer Triangle of Deneb of Cygnus, Vega (Lyra), and at the southern apex, Altair (Aquila). Look directly north of Altair to find dimmer Sagitta, the Arrow, and then to the northwest to admire pretty Delphinus, the Dolphin, which looks like a hand with its finger pointing back down to Sagittarius.
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