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About The nugget. (Sisters, Or.) 1994-current | View Entire Issue (April 10, 2019)
18 Wednesday, April 10, 2019 The Nugget Newspaper, Sisters, Oregon Stars over Sisters By Ron Thorkildson Correspondent Astronomers estimate that more than two-thirds of all stars have one or more companions to accom- pany them in their journey through the cosmos. Our sun, however, seems to be going it alone in this regard, for despite an exhaustive search no stellar partner has yet been found. But perhaps we9re better off that the sun is a solitary star, since hav- ing two of them in our sky might severely limit our ability to see other celestial wonders that a dark night sky affords. A visual double star con- sists of two stars that appear to lie in close proximity to each other in the eyepiece of a telescope that is usu- ally seen as a single star to the unaided eye. There are two basic types of these objects4optical doubles and physical doubles. An optical double is the chance alignment of two stars that look like they are near each other, but are actu- ally very far apart in space. When two stars really are neighbors and gravitation- ally bound to one another, they9re referred to as a phys- ical double, or binary star. Many observers with telescopes derive a great deal of satisfaction from viewing double stars. To professional astronomers, and even amateurs who have the right kind of equipment, there is genuine science to be gained. It turns out that carefully measuring binary stars can yield the total mass of a double-star system. This information is of cru- cial importance to theorists working on stellar evolution. All one needs to mea- sure double stars is a good telescope on a solid, motor- ized equatorial mount, and an auxiliary piece of equip- ment called a micrometer. A micrometer is a device that consists of an eyepiece and two parallel thin fila- ments or threads, one that is fixed while the other can be moved by turning a screw head upon which is marked a finely graduated scale. As it turns out, only two pieces of information are necessary to determine the orbit of a binary star: the position angle and separa- tion of the pair. In double- star lingo, the brighter of the two stars is referred to as the primary, the dimmer as the secondary. The position angle describes the dimmer star9s location with respect to the primary, expressed as the number of degrees from true north. The sepa- ration of the two stars is a straightforward measure (in arcseconds) of the apparent distance between them. This is precisely the information that the micrometer was designed to ascertain. When one applies these data to a blend of Newton9s law of gravitation and Kepler9s third law of orbital motion, the mass of the double star system can be calculated. But casually viewing doubles can also be a very rewarding exercise in its own right, as no two pairs are exactly alike. The attri- butes of particular interest are the separation, relative brightness and color contrast of the two stars. What is the closest stellar separation your telescope can detect? What colors, if any, can you see? The following three dou- ble stars are among the finest in the spring sky. Magnitude (mag) refers to the bright- ness of a star; the lower the number, the brighter the star. Separation (sep) is the apparent distance between the two stars, measured in arcseconds. The percep- tion of color in stars is often highly subjective and can depend on the type and qual- ity of the observing instru- ment, atmospheric condi- tions, and eyesight of the observer. The colors listed here are those most often found in the literature on the subject. DECAPODA (iota Cancri) in the constellation of Cancer: mags: 4.2, 6.6; sep: 30.5; color: gold and blue. ALGEIBA in the constel- lation of Leo: mags: 2.6, 3.8; PHOTO BY RON THORKILDSON A micrometer for measuring double stars is attached to one of Sisters High School’s 8-inch Schmidt-Cassegrain telescopes. sep: 4.5; color: both yellow. COR CAROLI in the con- stellation of Canes Venatici (just below the handle of the Big Dipper): mags: 2.9, 5.4; sep: 19.6; color: white-to- slightly yellowish. <For some reason the sight of two stars lying very close together is an extremely satisfying one&=, from an article by Henry J. Phillips, entitled Doubles, Binaries and Multiple Stars, Astronomy Magazine, November 1976. CHECK OUT this week’s Nugget inserts! Serving Sisters Since 1976 ng on i o g t e g o Need t e’ve W ? s t c e j o spring pr ing you need! th FREE got every Local Delivery Lumber • Hardware • Paint Fencing & Decking • Doors & Windows ows Hours: M-F 8 to 5, Sat. 8 to 4:30, Closed Sundays 440 N. 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