Department of Physics University of Durham Level One

 3. Barnard's Star

Edward Emerson Barnard (1857-1923) was one of the most remarkable astronomers in the late 19th/early 20th century. "Known in his day as a man destined to be `famous as long as fame shall last', few figures rivaled his renown, and today he continues to be remembered for the legendary keenness of his sight and his fantastic dedication to astronomy" ( Sheenan 1995). He is known for his work on planets, comets, double stars, bright and dark nebulae and globular clusters. As a young amateur astronomer he discovered so many comets that he was offered a job at the Lick Observatory. In 1892 he discoverd the fifth satellite of Jupiter, Amalthea. Also in 1892 he made the first photographic discovery of a comet. He published over 900 articles.

Barnard took over 4000 photographic plates of the Milky Way. These contained a rich source of information on a host of astronomical objects like variable stars. On a plate taken in May 1916 he found a `new' 10th magnitude star that was not present on a plate taken in August 1894. At first he considered that the `new' star was a nova. However on a more detailed inspection of the August 1894 plate he found another 10th magnitude star four arcminutes away which was not present on the 1916 plate. He then looked at a plate taken in 1904. While neither of the previous two stars were visible, a `new' star was present in a position that was roughly half way between the two previous `new' stars. The close alignment of these three `new' stars lead Barnard to realise that all these `new' stars were caused by a star with a very large proper motion. He confirmed this by examining another plate taken in April 1907. This star, now called Barnard's Star, stills holds the record for the star with the largest proper motion. While the nearest stars typically have proper motions of about an arcsecond per year, Barnard's star had a proper motion of 10.3 arcsecond per year. This motion corresponds to the star travelling half a degree (the Moon's diameter) in only 175 years.

At a distance of 1.821 parsecs, Barnard's star is the fourth-nearest star; only the three stars in the Alpha Centauri system are closer. The large apparent motion of Barnard's star is a result of its nearness and its unusually high space velocity. Early observations of its path over many years seemed to find evidence for a wobbling motion that may have been caused by the presence of planets. Unfortunately recent studies (e.g. Benedict et al. 1999) have failed to confirm this result.

Burnham's Celestial Handbook contains an excellent short article on Barnard's star. A copy of this is provided in the Lab. This is essential reading for the experiment and you should read it now.

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