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Sunday, September 29, 2013
In more years than not, October brings great weather for stargazing. Many folks spend clear, dark nights looking upward at the Milky Way, appreciating its wispy glows and innumerable sparkling lights. The rest of October’s sky appears rather muted in contrast and, consequently, is often overlooked.
One area which receives little attention lies east of the Teapot of Sagittarius and south of the Summer Triangle’s southernmost star, Altair. Low in the south at 8:30 p.m. stands the dim zodiacal constellation Capricornus.
City observers may be able to spot Capricornus’ two major stars, Delta and Beta Capricorni, shining like bookends at either end of the constellation, but little else. Skywatchers in the country, though, should have no trouble seeing its entire inverted chevron shape, and sharp eyed observers should notice some unusual stellar configurations in the constellation’s upper right corner.
Beta Capricorni, also called Dabih, can be found along an imaginary line beginning at the brightest star of the Summer Triangle, Vega, and continuing south through Altair. While it is only a moderately bright star, there is more to it than meets the unaided eye.
Through steadily held and sharply focused binoculars, a faint companion star, Beta Capricorni 2, lies just west of Dabih’s dominant component, almost hugging it.
Beta 2 might be difficult to distinguish from the much brighter Beta 1 because of the closeness of their separation and of their mismatched brightnesses. These two 300-light-year-distant stars are weakly gravitationally bound, taking an estimated 700,000 years to circle each other. Both stars, in turn, are multiple, yielding a total of at least six suns for the Dabih system.
Directly above Beta shimmers a dimmer star, one that needs a relatively dark sky to spot. Keen eyed observers will notice something odd about Alpha. For many people, it appears blurry. To those with excellent eyesight, it appears as two closely separated stars of similar brightness. Binoculars easily reveal the two components plus a third star, Nu, twinkling to their left.
Alpha 1 and Alpha 2 are nowhere near each other in space and are not gravitationally associated. They just coincidentally share the same line of sight viewed from Earth. Alpha 2 lies 109 light-years from us while Alpha 1 shines six times farther.
Another blurry stellar arrangement twinkles to Beta’s lower left. Again, keen eyed observers at a dark site will be able to barely pick out the stellar triangle composed of Rho, Pi, and Omicron Capricorni. These three stars are themselves each part of multiple star systems giving, instead of three suns, a total of seven.
This area of Capricornus is featured on Oct. 12 in a demonstration of our moon’s orbital motion. Look at the first quarter moon, beginning just before 9 p.m.
Immediately to the moon’s left twinkles Beta Capricorni (Dabih). Properly focused binoculars will give a clearer view if the bright half of the moon is placed just outside the field’s right rim.
By 9:10 the dark lunar edge approaches faint Beta 2. If the moonlight’s glare isn’t too strong, a few minutes later Beta 2 can be seen suddenly disappearing behind the moon, leaving Beta 1 standing alone in the moon’s path. Eight minutes later, as the moon continues advancing east in its orbit, it covers, or “occults,” Beta 1. Less than 75 minutes later, the occultation ends when the moon moves sufficiently eastward for Beta 1 to pop out behind the bright rim of the moon. (The moon’s glare will certainly prevent catching Beta 2’s emergence eight minutes before Beta 1.)
After admiring October’s Milky Way, look in western Capricornus and count its starry secrets. How many can you see?
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