Spectroscopy (3)

A spectroscope uses a series of prisms or a diffraction grating - a device that diffracts light through fine lines to form a spectrum - to split light into its constituent wavelengths. Before the era of photography, an astronomer would view the spectrum produced with the eye, but now it is mostly recorded with an electronic detector called CCD. This 19^th century spectroscope uses a prism to split light.

During the solar eclipse of 1868, a number of astronomers picked up a new spectral line in the upper surface of the Sun, the chromosphere. The English astronomer Lockyer realized that the line did not coincide with any of the known element. The newly discovered element was named helium (helios is Greek for the sun god). It was not until 1895, however, that helium was discovered on Earth.

Ångström was a Swedish astronomer who mapped the Fraunhofer lines in the Sun's spectrum. The units needed to measure the wavelengths of the colours corresponding to these lines were so small that Ångström had to invent a new unit of length. The Ångström (symbol Å) is 10^-10 metres.