READING THE SIGNALS
In 1859, German physicist Gustav Kirchhoff showed that each chemical element produced characteristic patterns of lines in the spectrum of the Sun. He correctly interpreted the bright spectral lines as the emission of light by particular chemical elements, and the dark lines as the absorption of light by the same elements. This meant spectral analysis could reveal, for instance, that the Sun contains sodium.
By 1863, spectroscopy had advanced enough to allow English astronomer William Huggins to publish lists of stellar spectral lines. He confirmed that the Great Nebula in Orion was gaseous, and detected hydrogen, which had already been noted in the Sun, in the spectrum of a nova— the first evidence that all stars contained hydrogen. Huggins also used spectroscopy to determine the speed and direction of the star Sirius's movement.
Progress in photography brought a further leap in astronomical research. Until the early 1800s, cameras were primitive pihole types, but by the 1840s, lenses, mirors, and better film emulsions were available. Successful photographs of the Moon galvanized astronomers into photograping the Sun, which became a routine matter in the 1870s.