Following Edmund Halley’s discovery of proper motion in 1718, James Bradley (1693-1762) in 1746 noted that it was necessary to separate proper motion from the apparent motion caused by the moving Solar System carrying Earth with it.
In 1760 Tobias Mayer (1723-62) noted that if we walk in a forest, the trees in front of us appear to open out and those to the rear seem to close together. Similarly, if the Solar System is moving towards a certain point, the solar apex, the stars would appear to move away from this apex in a great circle towards a point in the opposite direction, the solar antapex.
In 1783 William Herschel having studied the proper motions of seven bright stars was able to plot the Sun’s motion through the Galaxy and deduced that the Sun is moving towards a point in the constellation of Hercules. By 1937, from a study of the proper motions of several hundred stars Friedrich Wilhelm August Argelander (1799-1875) obtained a solar apex not far from that proposed by Herschel.
In 1751-3 at the Cape of Good Hope, Nicolas Louis de Lacaille (1713-62) surveyed the southern skies. He discovered twenty-four new nebulae and clusters and charted the positions of nearly 10,000 stars. In 1847 Thomas Galloway (1796-1851) analysed the proper motions of eighty-one of these and obtained an apex position that matched the position derived from the northern stars.
Barnard’s Star has the largest proper motion of any star known. Discovered in 1916 by Edward Emerson Barnard (1857-1923) it is the third closest star to the Sun, 6 light years away and moving across the sky at 10.31 arc seconds (about 1/200th of the Moon’s angular diameter) each year.
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