Over the years, many people have tried to find the distances to the stars. Robert Hooke outlined in 1674 the problems of looking for annual motion of stars and Isaac Newton tried to calculate the distance of Sirius by comparing its brightness to that of the Sun. However, until the 19th century, telescopes were not sensitive enough to detect the very tiny parallax motions. The first person to succeed was F. W. Bessel who in 1838 measured the parallax angle of 61 Cygni .
He did this by using the double star method. He observed two stars that appeared in his view to be one (Figure 1). Over a six month period he found that two stars became visible separately, the closer one moving relative to the background stars (Figure 2).
* Click here to find out how Bessel found the distance of 61 Cygni
* Click here to learn about modern developments in measuring parallax
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