William Herschel, who collaborated with his sister Caroline, announced his discovery of binary star systems in 1802. Several years later in 1814, Joseph von Fraunhofer is the first to observe dark lines in the Sun's spectrum, and pioneers the use of diffraction gratings to observe the nature of light being given off from objects in the night sky. This basic process has enabled scientists ever since to analyse the composition of stars and galaxies. In 1837, Willheim Beer, a German banker and amateur astronomer, published the first accurate map of the moon. And the year after that, Friedrich Bessell determined the distance of the star 61 Cygnni.