Stellar spectrograph

Spectrographs like astrographs were photographic apparatus attached to telescopes to record the stellar activity. They were similar to the spectroscope except the photographic plate was used instead of the eye-piece.

The spectroscope used prisms to spread stellar images out into lines of spectral wavelengths rather than providing an image of what was seen through the lens of a telescope. The light from stellar objects is passed through a slit and collimator to produce a parallel beam of radiation passed through a prism, or prisms, to disperse it into different wavelengths.

It was an American, Henry Draper, who successfully introduced the use of the camera to photograph spectra and thus introduced the spectrograph to the world. His first successful photograph was taken in 1872 and was of the star Lyrae. In 1876 Draper made a piece of apparatus he called a 'spectrograph' which comprised of a "Browning direct-vision prism train and a 7-inch Voightlander portrait lens". Draper conducted numerous experiments on the arrangement of prisms and lens, but he died unexpectedly in 1882 before his experiments were finalised.

The work of Draper was carried on by another pioneer stellar photographer, Professor Pickering, Director of the Harvard College Observatory. In 1885 Pickering installed an eight inch Voigtlander lens configured by Clarke at Cambridge. He later worked on the Bruce telescope which was able to impress as many as 400,000 stars on a single 14 x 17 inch plate due to the great aperture of the lens combined with a relatively short focal length.

These telescopes have been used for both spectral and point photography but the use of spectroscopes attached to telescopes has afforded the best results for stellar photography, allowing many more stars which could not be seen with the naked eye to be measured for the first time by astronomers.

This spectroscope arrived at Sydney around 1915 and was made by the instrument maker Adam Hilger who in 1875 opened up his premises at 192 Tottenham Court Road, London. Although significant for being made by one of the leading instrument makers it is reputed to have been little used during its tenure at the observatory. This was probably through no fault of the instrument which although very sensitive to small changes in focus was still in use as late as 1939. [see associated exercise book (H9955-5 with graphs and notes made using the spectrograph]