From: parish@cactus.org (Tom Parish)
Subject: SKYWATCH Jan 24-30 Seeing Double
Followup-To: poster,kanipe@astro.as.utexas.edu
Organization: Capital Area Central Texas UNIX Society, Austin, Tx
Date: Mon, 25 Jan 1993 02:08:57 GMT

SKYWATCH 1993                                                Turning Point
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 This Week      January 24 through January 30 - SEEING DOUBLE
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 Planets        * Mercury is in superior conjunction (behind the sun) on 
                  the 23rd and hence cannot be seen this month.
                  
                * Venus is the bright evening star in the southwest.
                
                * Mars rises at sunset in Gemini and is visible all night.
                
                * Jupiter rises around midnight in the constellation Virgo.
                
                * Saturn is too near the sun to be seen. It reappears in 
                  the morning sky in mid to late April.
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 Events         26 The moon is 28 km (252,293 mi).
                
                26 Venus is south of the crescent moon in the southwest
                   just after sunset.
                
                30 First quarter moon.
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 Anyone for     Perhaps you got a new telescope for Christmas and by now 
 Double Stars?  you've had your fill of planets and the moon. Okay, what
                else is there to look at?
                
                One of the nice things about the night sky is there is an 
                inexhaustible supply of interesting objects to look at up
                there, especially if you have access to a telescope.
                Offhand, I'd suggest you try your hand at double stars. A
                double star is a system of two or more stars that are
                either gravitationally bound to each other or merely lined
                up in space so that they look related. Roughly three-
                fourths of all the stars we see in the night sky are double
                or multiple stars. In fact, had the planet Jupiter been
                just about 85 times more massive than it was when it
                formed, our solar system would have had two suns instead of
                one.
                
                A good place to begin is in the constellation Orion, now
                fine and large in the south. Orion contains some very fine
                double stars. Anyone familiar with the Orion Nebula, a tiny
                star cloud hanging just below the three stars that make up
                "Orion's belt," knows about the most famous multiple star
                system in the sky, the Trapezium. Four bright members can
                easily be seen near the nebula's core making a tight fist
                of stars. At least four or five other members are also 
                associated with this quartet, two of which can be detected
                with a 3-inch telescope under good seeing conditions at
                high magnifications.  In fact, the Trapezium sits at the
                center of a cluster of as many as 300 fainter stars that
                condensed from the surrounding nebulosity as little as half
                a million years ago. Sure the nebula is stunning, but zoom
                in on the Trapezium and see a star cluster in the making!
                
                Bright blue Rigel, Orion's westernmost star, is also a fine,
                though challenging, double star. Rigel's companion is a
                tiny, faint point of light nestled in the glare of the
                great star. You need to use a medium-power eyepiece in your
                telescope and you have to look very carefully. The dramatic
                differences in brightness make this double star a
                spectacular site. Rigel and its companion have shown no 
                change in separation since they were first measured in 1831.
                Nonetheless, they are thought to be gravitationally bound to
                one other.
                
                A favorite double at star parties is Lambda Orionis, which 
                marks Orion's head. Like Rigel, the Lambda stars have not
                shown any change with respect to each other since the
                1830s.  But whether or not this is a true binary, Lambda
                certainly forms a striking pair in the eyepiece. The
                companion lies just northeast of Lambda and is easy to see
                in a small telescope.
                
                These are just a few of the thousands of interesting double
                stars visible in small telescopes. After seeing these, you
                may find yourself pointing your telescope at each bright
                star in the sky to see if they, too, have companions. Don't
                be surprised when you discover that some of them do! 
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 Author         Jeff Kanipe. Jeff is also editor of Star Date Magazine.
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 Publisher      McDonald Observatory at the University of Texas at Austin.
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 For More       Write to Star Date at 2601 University, Room 102, the
 Information    University of Texas at Austin, Austin, TX 78712
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 Contact        kanipe@astro.as.utexas.edu  Editor Star Date Magazine
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 Legal          Copyright 1992 The University of Texas McDonald Observatory.
                Material is intended for personal education and should not
                be rebroadcast in any written or verbal form without
                prior permission from the University of Texas.
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 Jan 25-31      you see in the heavens isn't necessarily what you get.
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                Earth. That's right here on Star Date.  Nature's fireworks
                in the early-morning sky after this.
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                                    parish@cactus.org
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