The Spectroscope

The Spectroscope

Light dispersion of a mercury-vapor lamp with a prism made of flint glass.
When light strikes or enters a prism, it is dispersed into component colors. This is an example of spectroscopy. Light dispersion by D-Kuru is licensed under CC BY-SA 3.0

A star’s color tells us a lot about the star: its temperature and perhaps even the star’s life cycle. But to dig a bit deeper, scientists use a tool called the spectroscope and spectroscopy. In 1814, Joseph van Fraunhofer invented the modern spectroscope. The spectroscope basically uses a prism or diffraction grating to break light into its component colors, producing a spectrum. There is also a slit, where the light enters, and a telescope-like focuser.

The heart of the spectroscope — the component which breaks light into its component colors, is either a prism or a diffraction grating. Think of the diffraction grating as many small prisms on a thin sheet of plastic or glass; 500 or more rulings per inch. The CD is a good analogy to a diffraction grating.

The bottom of a CD is shown with colors illuminated by a light reflection.
The grooves of a CD can act as a diffraction grating, producing colors when light is reflected off of the CDInterference-colors by Luis Fernández García is licensed under CC BY-SA 2.0

A spectroscope can be mounted on a telescope, collecting light from one object, such as a star or galaxy, to be passed through the spectroscope for analysis. (1)

Lick Observatory’s Spectroscope, 1898. The actual spectroscope, which looks like a tube, is attached to the back of the telescope is in the lower left of the illustration.
Lick Observatory’s Spectroscope, 1898. The actual spectroscope, which looks like a tube, is attached to the back of the telescope is in the lower left of the illustration. Star-Spectroscope by Julius Scheiner is in thePublic Domain