Though now obsolete, the sky’s other bull, Taurus Poniatowski, once grazed to the left or east of the Ophiuchus the Serpent Bearer.
In 1777 a Polish-Lithuanian astronomer Marcin Poczobutt chose to honor the Polish king Stanislaus Poniatowski by creating a small constellation in his honor named Taurus Poniatovii (Poniatowski’s bull). The little figure was scraped together from stars alongside the much larger Ophiuchus the Serpent Bearer.
Like a lot of small, faint groups created by 18th century astronomers, the bull never survived except in the history books. One of a dozen or more obsolete constellations, the stars of Poniatowski’s bull eventually were parted out to Ophiuchus and Aquila the Eagle.
The southern sky around 10:30 p.m. in early to mid-July. Ophiuchus is a large constellation above Scorpius and its bright, red star Antares. Our featured double star, 70 Oph, lies just to the left or east of Beta Oph. Maps created with Stellarium
The face of the bull is a stellar “V”outlined by the 4th magnitude stars 67, 68 and 70 Ophiuchi. Fainter stars extend the V further north. In binoculars they resemble a dimmer version of the Hyades in the real Taurus the Bull. From suburban areas and the countryside, it’s easy to see the group about halfway up in the southern sky at nightfall around 10:30 p.m.
Close up of 70 Oph located about 4 degrees to the left or east of the easily visible Beta Ophiuchi.
You’re welcome to seek out the obsolete bull for its own sake, but if you own a telescope, point it at 70 Ophiuchi (Oph) the next clear night. This unassuming star is one of the sky’s most colorful doubles.
Located just 16 light years away, the stars of 70 Oph revolve about their common center of gravity in just 88 years.
That’s short enough to watch them through at least half an orbit during your lifetime. Most doubles show no noticeable change over hundreds or even thousands of years because of greater separation and distance.
This diagram shows the dimmer 6th magnitude companion of 70 Oph in orbit about the brighter one (on crosshairs). The two are about 6 arc seconds apart and easily splittable in a small telescope. South is up and east to the right in the diagram. Credit and copyright: Richard Dibon-Smith
Their average separation of the two stars is nearly the same as the distance of Uranus from the sun. When closest back in 1989, they were a little more than a billion miles apart or Saturn’s distance from the sun. The duo reaches maximum separation in 2028 at 3.2 billion miles, similar to Pluto’s average distance.
Currently they’re easily divisible with a small telescope using a magnification of 50x or higher. The fainter companion lies to the southeast or upper right of the brighter as seen in a typical reflecting telescope.
How 70 Oph looked to my eye last night at 76x in a 10-inch telescope. Illustration: Bob King
Classified as orange dwarfs, both stars are smaller, cooler and less luminous than the sun. These characteristics make 70 Oph one of the most colorful pairs in the sky as I found out last night when viewing it through my 10-inch scope.
The brighter star is yellow orange; its fainter companion shines a rich red. Strongly colored stars so close together make a thrilling sight in any telescope. Take a look for yourself and see what you think.
While you’re in the area, make a second stop above the top of Ophiuchus at Alpha Herculis, the brightest star in Hercules the Strongman. This is another colorful double star with a bright red-orange supergiant orbited by a fainter greenish companion separated by about 5 arc seconds.
It’s estimated that at least half of the stars in the Milky Way galaxy are double or multiple. You could easily spend all night hopping from one to the next and barely scratch the surface. To help you in that quest, here’s a list of 100 of the best.