Nu Scorpii – A “Double-double” Challenge in Scorpius
by Glenn Chaple
I first met nu Scorpii in the summer of 1971. Using a 3-inch f/10 reflector and magnifying power of 60X, I saw the same wide (41 arc-second) magnitude 4.2 and 6.6 double star that the German astronomer Christian Mayer had discovered nearly two centuries earlier. At the time, I had no idea there was more to be seen.
Neither did the American astronomer Ormsby M. Mitchel (who would later become a decorated Civil War general) when, in 1846, he eyed nu Scorpii with the 11-inch refractor at the Cincinnati Observatory. He was able to split the fainter star into its magnitude 6.6 and 7.2 components, which were 1.1 arc-seconds apart at the time. In 1873, the eagle-eyed double star observer S. W. Burnham outdid Mitchel by detecting the duplicity of the brighter star when its magnitude 4.4 and 5.3 components were a mere 0.3 arc-seconds apart. This was an amazing visual accomplishment, as Burnham made the discovery using a 6-inch refractor!
In the ensuing decades, these two pairs (designated Mitchel 2 and Burnham 120) widened and, by the early 1900s, were within reach of medium aperture scopes. In 1905, Agnes Clerke wrote that nu Scorpii is “perhaps the most beautiful quadruple group in the heavens.” Other astronomers likened it to the better-known “Double-double” epsilon Lyrae.
Today, the two binary stars that comprise the nu Scorpii system are wider than ever – 2.4 arc-seconds for Mitchel 2 and 1.3 arc-seconds for Burnham 120. Splitting them will still require planning and patience. Because of its southerly declination, you’ll have to wait until nu Scorpii is as high above the horizon as possible (around 10pm on a mid-June evening). Optimum seeing conditions are a must, and you’ll need an optically sound telescope of at least 6-inch aperture and a 200X-plus magnifying power.
Was Agnes Clerke’s assessment of nu Scorpii accurate? Does it actually outrank the celebrated epsilon Lyrae in visual splendor? You won’t know unless you give each a telescopic examination.