The most celebrated star in the constellation Ophiuchus is not visible to the unaided eye, nor is it easy to find in small telescopes. Yet it is worth hunting for, because it is the next-closest star to the Sun after the triple system Alpha Centauri, which is too far south for most of the Northern Hemisphere to see.
Discovered by the American astronomer Edward Emerson Barnard at Chicago’s Yerkes Observatory in 1916, Barnard’s Star is a red dwarf, with a radius 15% that of the Sun. Because the star is only light-years away, it veritably screams across the sky at a break-neck pace of 10 arcseconds per year. While this displacement is but the angular size of a US nickel seen at a distance of half a mile, it is nevertheless a celestial record. Over the average human lifetime, the star will move by a quarter of a degree, nearly half the angular diameter of the full Moon.
In addition to its movement across the sky, Barnard’s Star is also approaching the Sun. Its proper motion (the measurement of its change in position in the sky over time) is gradually increasing, and will reach 26 arcseconds per year some 10,000 years from now. At that time the star will be 3.8 light-years away, closer even than Alpha Centauri is today.
In the 1960s and 1970s the Dutch-American astronomer Peter Van de Kamp reported an apparent wobble in the proper motion of the star, which he attributed to the presence of two orbiting planets similar in size to Jupiter and Saturn. This was not confirmed, and the star’s wobble seems to have been the result of changes in the position of the telescope’s lens. Barnard’s Star is now officially “planetless”, though that status could dramatically change as technology improves.
The finder map below will help you locate this elusive but fascinating object. The guide star to Barnard’s Star is 66 Ophiuchi, a 5th-magnitude slightly variable star to the left of Beta Ophiuchi.
With a visual magnitude of +9.6, Barnard’s Star is 15 times fainter than the unaided human eye can see, but a small department-store refractor will easily bring it into view. Observe it over a period of years so that you, too, can detect its motion against the starry background.
20 Aug, 2013
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