When Richard last visited us, back in 2007, he told us all about the invention and development of planeteria. This time, he chose to speak about spectroscopy, one of the most important tools of modern astronomy.
The first man to split white light into its component colours was Isaac Newton in 1666 and he gave the resultant rainbow the name spectrum, the Latin word for ghost.
Light is an example of electromagnetic radiation, the waves of red light being about twice as long as those of blue light, but still tiny, in the order of 700 nm in length (1 m= 1,000,000,000nm).
Over the following three and a half centuries other types of electromagnetic rays were discovered having wavelengths longer or shorter than those of light: invisible to the eye but detectable by various instruments.
William Wollaston found that the spectra of stars were crossed by dark lines and Joseph Fraunhofer later found around 600 of these. The absorption lines and the corresponding bright emission lines were produced by specific elements in the laboratory sample or star, thus giving astronomers the ability to find out for the first time what stars were made of and how hot they were. They also enabled chemists such as Robert Bunsen and Gustav Kirchoff to discover hitherto unknown elements in terrestrial minerals.
In 1842, Christian Doppler described the apparent change in pitch of a sound wave coming from a source moving towards or away from an observer. A similar effect with light waves enabled astronomers to determine the radial velocity of a star or galaxy.
Many types of object have been categorised using spectroscopy, such as quasars, white dwarf stars, exoplanets and spectroscopic binary stars.