Celestial Events 



Getting Through the Night 



by Gail S. Cleere 



The vernal equinox occurs at 3:28 p.m., 

 EST, on March 20, marking the beginning 

 of spring in the Northern Hemisphere. The 

 vernal equinox also marks a place in the 

 sky where the celestial equator (the earth's 

 equator stretched into space) and the eclip- 

 tic (the path of the sun across the sky) in- 

 tersect. These imaginary lines also inter- 

 sect at the autumnal equinox, but the 

 vernal equinox is special; it is used as the 

 standard reckoning point for determining 

 the position of every object in the sky. On 

 the vernal equinox, the sun's right ascen- 

 sion and declination (the celestial equiva- 

 lents of longitude and latitude) are both 

 zero. This position is also called the First 

 Point of Aries (even though over the years 

 it has drifted into neighboring Pisces). 



Most astronomical outsiders are less 

 than thrilled with this dry, mathematical 

 definition of spring, the season that brings 

 us warmer days, flowers, and green buds. 

 Since ancient times, however, people have 

 used the vernal equinox to mark the pas- 

 sage of the seasons. On the equinox, 

 which means "equal night," the days and 

 nights are roughly twelve hours long 

 everywhere on the planet. Also on the 

 equinox, the sun rises precisely in the east; 

 and at local noon, it reaches an altitude 

 that is halfway to the highest point it 

 reaches in the sky all year. This event sig- 

 nals that the harsh days of winter are fi- 

 nally over Because of the unseen tilting of 

 the earth to the sun, spring finally arrives. 



We no longer depend on the sky to mark 

 the seasons, so most of us are not in the 

 habit of keeping track of the shifting con- 

 stellations and the whereabouts of the 

 moon and planets each night. But for those 

 who wish to give it a ti^y, help is now as 

 close as the nearest telephone. Every state 

 in the Union has at least one astronomy 

 club that can provide information on ce- 



lestial highlights. One directory is pub- 

 lished every March by Astronomy maga- 

 zine. An even better source of information 

 is the Astronomical Directory in Sky and 

 Telescope magazine's September 1992 

 issue, in which twenty-nine phone num- 

 bers are listed as "telephone hotlines" for 

 astronomical information and notes about 

 the current night sky. Some of these hot- 

 lines are provided by museums and plane- 

 tariums, such as the Smithsonian's Air and 

 Space Museum in Washington, D.C., and 

 the Hansen Planetarium in Salt Lake City, 

 Utah. Some are run by astronomy clubs, 

 but these have mostly news about club 

 events and members. 



If taped messages go by too fast for you 

 (most have a three-minute limit in which 

 the announcer must describe the night sky 

 from horizon to horizon), a better solution 

 is a computer bulletin board (SIcy and Tele- 

 scope's September 1992 issue lists fifty- 

 one of them). If you have a computer and 

 a modem, you can gain access to them. 

 Some give the same text given on the as- 

 tronomy telephone hotUnes, and some are 

 entirely different. Now, armed with your 

 computer printout or your notes from the 

 telephone hotiine message, you are ready 

 to brave the night. 



As the sky darkens on clear March 

 evenings, and the lovely Pleiades and 

 Hyades pull Orion from the southern skies 

 to the western horizon, watch as Leo the 

 Lion lumbers up over the eastern edge of 

 the sky with his signature star, Regulus, in 

 the lead. Leo is easy to find if skies are 

 dark, for it is one of the few constellations 

 to actually look like what it's supposed to 

 be. Spica in faint Virgo is the next bright 

 star to come up over the eastern horizon. 

 Just about midnight, watch as the two stars 

 that mark the claws of the Scorpion reach 

 out toward Spica. These are Zubenel- 



genubi and Zubeneneschamali, now des- 

 ignated as part of the constellation Libra. 



And that mysterious bright object near 

 the Scorpion's southern claw? A quick call 

 to a hotline will reveal that it's Jupiter, the 

 planet that will Unger in the same area for 

 the rest of 1994. 



The Planets in March 



Mercury remains a difficult planet to 

 spot this month, although it is up in the 

 morning skies. The sun's closest neighbor 

 reaches greatest elongation west (28°) on 

 the 19th, but despite the large separation 

 from the sun, this is an unfavorable elon- 

 gation for Northern Hemisphere sky- 

 watchers because of the low angle of the 

 ecliptic. Perhaps the best time to try to 

 spot Mercury this month will be within a 

 few days of March 10, when you might 

 spy it looking like a bright zero-magnitude 

 "star" very low above the east-southeast 

 horizon about an hour before sunrise. On 

 the morning of the 24th, Mercury will 

 stand less than half a degree (about the 

 width of a full moon) south of Saturn. 



Venus slowly emerges from the glare of 

 the evening twilight this month, as the 

 time of its setting after sundown increases 

 from about forty-five minutes on the 1st to 

 ninety minutes on the 3 1 st. On the evening 

 of the 13th, look to the west shortly after 

 sunset and you should find a very young 

 crescent moon. Below and shghtiy to the 

 left of this delicate crescent, just above the 

 western horizon, you should find brilliant 

 Venus. 



Mars rises only one-half to one hour 

 before the sun this month. Shining at mag- 

 nitude -1-1.2, the red planet wiU be ex- 

 tremely difficult to see in the bright morn- 

 ing twilight. Mars passes Saturn on the 

 mornings of the 13th and 14th, but be- 

 cause of their low altitude and proximity to 



26 Natural History 3/94 



