• The nearby star 70 Ophiuchi is one of the best-known and widely studied binary star systems. It's found in an odd V-shaped collection of five stars called Poniatowski's Bull. This strange little asterism is easy to see with the naked eye from suburban skies; if you're in the city, try your finderscope or binoculars. 70 Oph is on the east side of the “V”; it's near the celestial equator, so it's visible from the northern and southern hemispheres.
• The two components of 70 Oph have magnitude 4.2 and 5.9; the brighter star is a yellow-gold while the fainter looks orange-red, with some observers reporting a tinge of violet. Move your telescope out of focus just a touch to see the colors well. Each star has an intrinsic brightness only a fraction that of our Sun.
• The components complete a revolution about each other in only 88 years. And because the system is only 16 light years away, the stars are close enough for you to resolve in a backyard telescope. So this is one of the few double stars you can see revolve about each other during a human lifetime.
• The average distance between the stars is about the same as the distance between the Sun and Uranus. The stars were closest together in 1989. Since then, their separation has quickly increased from 1.7 arc-seconds to about 5 arc-seconds. You'll need at least 100x to resolve them cleanly with a telescope.
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