THE SKY IN JULY AND AUGUST 



By Joe Rao 



Mercury is too dim and too close to the 

 Sun to see until the last few days of Ju- 

 ly. It passes through inferior conjunc- 

 tion, between the Earth and the Sun, 

 on July 18 and moves into the morn- 

 ing sky. Look for it at the end of the 

 month, low in the east-northeast sky 

 about forty-five minutes before sunrise. 



In August this speedy planet makes a 

 fine morning apparition, as it gains alti- 

 tude and reaches its greatest western 

 elongation on August 7. On that morn- 

 ing it shines at magnitude +0.1 and ris- 

 es nearly ninety minutes before sunup. 

 During the next two weeks Mercury 

 slowly drops back toward the Sun, but 

 as if to compensate, it grows progres- 

 sively brighter. On the mornings of 

 the 9th and 10th you'll find Mercury 

 roughly two degrees below brilliant 

 Venus. Then, on the morning of the 

 20th, Mercury shifts to just a little more 

 than one degree above Saturn. Two 

 mornings later, a slender crescent Moon, 

 less than thirty-six hours from its new 

 phase, appears to hover weD above Mer- 

 cury. By then, Mercury brightens to 

 magnitude —1.4, matching Sirius, the 

 brightest star in the sky. For the rest of 

 the month it disappears into the dawn. 



Venus shines brilliantly at magnitude 

 —3.8 in the morning sky. From the be- 

 ginning of July through the middle of 

 August it rises out of the east-northeast 

 sky just as dawn breaks. In August it 

 passes a couple of degrees above Mer- 

 cury on the mornings of the 9th and 

 10th. In the second half of August it 

 loses altitude noticeably as it begins its 

 plunge back toward the Sun. A nar- 

 rowing crescent Moon slides past Venus 

 on the mornings of the 21st and 22nd. 

 By the end of August Venus is rising a 

 bit more than an hour before the Sun. 



Mars starts July setting a little more than 

 two hours after the Sun. But the planet 

 is shining at only magnitude +1.8 — as 

 dim as it can get. Look for it low in the 

 west-northwest sky, beginning about an 

 hour after sunset. Don't confuse it with 

 Saturn, which is about three times 

 brighter, but well below and to the right 



of Mars. Ifyou are blessed with very clear 

 weather on the evenings of the 21st and 

 22nd, look for Mars hovering less than 

 a degree above and to the right of Reg- 

 ulus, the brightest star in the constella- 

 tion Leo, the lion. You'll probably need 

 binoculars to pick them up, but if you 

 do, you'll likely be impressed by the col- 

 or contrast between yellow-orange 

 Mars and bluish Regulus. 



This summer Jupiter is the most favor- 

 ably placed planet to view. At the start 

 of July it's shining brightly at magni- 

 tude —2.3 in the south-southwest sky 

 and doesn't set until around 2 A.M. lo- 

 cal daylight time. At the start of August 

 it's in the southwest at sunset and sets 

 around midnight. By the end of Au- 

 gust it's setting about two and a half 

 hours after sunset. Jupiter's retrograde, 

 or westward, motion among the stars 

 ends on July 6; thereafter, it starts shift- 

 ing back to the east and will approach 

 the star Zubenelgenubi, also known as 

 Alpha Librae in the constellation Libra, 

 the scales, for the rest of July and Au- 

 gust. By August 1 , the star and the plan- 

 et are within five degrees of each oth- 

 er, but the two bodies continue closing 

 in to a separation of less than two de- 

 grees by month's end. Look for Jupiter 

 at dusk on the 29th, hovering above 

 and to the right of a fat crescent Moon. 



Saturn, for the first couple of weeks of 

 July, can be spied low in the west-north- 

 west sky for about an hour after sunset. 

 Ultimately, however, the planet disap- 

 pears into the glow of evening twilight. 

 Use Mercury and brilliant Venus to 

 guide you to Saturn as it emerges into 

 the morning sky in late August. On the 

 20th, Saturn approaches to within 

 slightly more than one degree of 

 Mercury; both planets lie below and to 

 the left of Venus. A sliver of a crescent 

 Moon passes well above and to the left 

 of Saturn on the morning of the 22nd. 

 The next morning, Mercury and Venus 

 form the end points of a diagonal line 

 about eight degrees long against the sky, 

 while Saturn lies almost exactly halfway 

 in between. By the 26th, Saturn lies a 



half degree below and slightly to the left 

 of Venus. By the following morning it 

 is a half degree above and slightly to the 

 right of Venus. But compared with that 

 dazzling morning "star," Saturn appears 

 only a forty-eighth as bright. 



The Moon in July waxes to first quarter 

 on the 3rd at 12:37 P.M., and becomes 

 full on the 10th at 11:02 p.m. It wanes 

 to last quarter on the 17th at 3:12 P.M. 

 and to new on the 25th at 12:31 A.M. 

 On the 20th a waning crescent Moon, 

 24 percent illuminated, occults, or pass- 

 es in front of, the Pleiades star cluster as 

 seen from eastern North America. That 

 early-morning event takes place about 

 a quarter of the way up in the eastern 

 sky. In some ways it will be the reverse 

 of the occultation of April 1 . This time, 

 between roughly 3 and 5 A.M. eastern 

 daylight time, stars disappear along the 

 Moon's sunlit crescent and reappear 

 from behind the dim earthlit edge. 



In August the Moon waxes to first 

 quarter on the 2nd at 4:46 A.M., and to 

 full on the 9th at 6:54 A.M. The Moon 

 wanes to last quarter on the 1 5th at 9:5 1 

 P.M., and returns to new on the 23rd at 

 3:10 P.M. The Moon then comes back 

 to first quarter for the second time in 

 August on the 31st at 6:56 p.m. 



Earth reaches aphelion, its farthest point 

 from the Sun, on July 3 at 7 P.M.; the two 

 bodies will be 94,507,915 miles apart. 



The Perseids are one of the most active 

 and reliable meteor displays of the year. 

 Unfortunately, the bright light of a 

 waning gibbous Moon — four days past 

 full — will largely spoil this year's Per- 

 seid show. The show peaks on the 

 morning of August 13. You might want 

 to watch anyway, because even in the 

 brightest moonlight a brilliant Perseid 

 fireball occasionally blazes across the 

 sky. The best time to watch is between 

 midnight and dawn. Lie down and gaze 

 at the part of the sky directly away from 

 the Moon. 



Unless othemnsc noted, all rimes are given 

 in eastern daylight time. 



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NATURAL HISTORY July/August 2006 



