THE SKY IN SEPTEMBER 



Mercury is at superior conjunction (be- 

 yond the Sun as seen from Earth) on 

 September 1, and enters the evening 

 sky. Unfortunately for observers in the 

 Northern Hemisphere, Mercury lies 

 well south of the Sun, toward the west- 

 southwest at sunset, and so it never gets 

 much above the horizon all month 

 long. Even at the end of September the 

 planet is still mired deep in bright 

 evening twilight and sets less than forty- 

 five minutes after sunset. Observers in 

 the southern United States (and farther 

 south) might be able to spot it with 

 binoculars, but it's a long shot at best. 



Venus begins the month rising a bit 

 more than an hour before sunrise. But 

 throughout the month it's also rapidly 

 sliding toward the Sun, so by month's 

 end it rises only about a half hour be- 

 fore the Sun. In the end, even its great 

 brilliance (magnitude -3.9) can't keep 

 it from getting lost in the glare of the 

 bright morning sky. On the morning 

 of the 6th, Venus comes within just 

 three-quarters of a degree of the bluish 

 star Regulus, in the constellation Leo, 

 the lion. You may need binoculars to 

 detect Regulus so low in the dawn; it 

 shines only 1/130 as bright as Venus. 



Mars is too close to the Sun this month 

 to be seen. It reaches conjunction with 

 the Sun in late October and remains out 

 of sight until it returns as a morning 

 "star" in December. 



Jupiter is visible in the southwestern 

 evening sky at dusk, setting just after 

 10 P.M. local daylight time at the be- 

 ginning of September. By the end of 

 the month it is setting below the west- 

 southwestern horizonjust after the end 

 of evening twilight — around 8:30 RM. 

 Between the 6th and the 17th, Jupiter 

 lies within one degree of the star 

 Zubenelgenubi, in the constellation 

 Libra, the scales. The closest approach 

 comes on the 1 1 th, when the big plan- 

 et passes a half degree to the upper right 

 of the star, their third close encounter 

 this year. On the 25th Jupiter lies to 

 the upper left of the crescent Moon. 



By Joe Rao 



On the following evening, it appears 

 to the Moons upper right. 



Saturn, now in Leo, continues to climb 

 progressively higher in the east-north- 

 eastern sky throughout the month. Now 

 shining at magnitude +0.5, it rises 

 around 4:45 A.M. local daylight time at 

 the start of September, and at about 3 

 A.M. by the 30th. Any telescope magni- 

 fying more than thirty times can reveal 

 the famous ring system; Saturn's rings 

 are tipped 15.1 degrees toward Earth at 

 the start of the month, but the angle 

 closes to 13.7 degrees by month's end. 



The Moon is full on the 7th at 2:42 P.M. 

 It wanes to last quarter on the 14th at 

 7:15 A.M. and becomes new on the 22nd 

 at 7:45 a.m. As September ends, the 

 Moon waxes to first quarter on the 30th 

 at 7:04 A.M. 



A small partial lunar eclipse is vis- 

 ible on the 7th from most of Europe, 

 Africa, Asia and Australia. The Moon 

 spends more than ninety-two minutes 

 inside the darkest part of the Earth's sha- 

 dow, which, at maximum coverage, 

 darkens about 19 percent of the lunar 

 diameter. There is also an annular (ring) 

 eclipse of the Sun on the 22nd. The en- 

 tire disk of the Moon will appear in sil- 

 houette against the Sun, producing a 

 dazzling ring of sunlight on the sky that 

 is visible along a path that crosses the 

 South Atlantic Ocean. The only land 

 areas that can see the annularity (just 

 after sunup) lie in Guyana, Suriname, 

 and French Guiana. A partial eclipse is 

 visible from eastern South America 

 and southern and western Africa. 



The Equinox occurs at 12:03 A.M. on 

 the 23rd. The Sun, which appears to 

 make its annual circuit of the sky along 

 the ecliptic, crosses the projection of 

 the Earth's equator against the sky and 

 plunges into the Southern Hemi- 

 sphere. Autumn begins in the North- 

 ern Hemisphere, while spring begins 

 in the Southern. 



Unless otherwise noted, all times arc given 

 in eastern daylight time. 



September 2006 NM URAl HISTORY 67 



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