Spectrograph and Spectroscopy

Spectroscopy is a fundamental tool that astronomers use to study the Universe. Spectrographs are instruments that are used to conduct spectroscopy. They provide scientists with the data they need to analyse the materials that make up stars, nebulae, galaxies and the atmospheres of planets.

Any object that absorbs or emits light can be studied with a spectrograph to determine characteristics such as its temperature, density, chemical composition, and velocity. Once the light enters the spectrograph it is split by a dispersive optical element into its different components (or wavelengths) in order to be studied. This optical element acts much like rain droplets that disperse the light to form a rainbow. This dispersed light is then focused onto a detector and it is seen as a spectrum. The spectrum’s pattern can be analysed by astronomers to decipher what atoms and molecules are present in the source. This helps them to understand the various physical and chemical characteristics of the source. In this way, Hubble’s images tell us what something looks like, while the spectral data tell us what it is and what it’s made of.

Hubble is equipped with two spectrographs: the Space Telescope Imaging Spectrograph, which was installed on the telescope in 1997, and the Cosmic Origins Spectrograph, which was installed in 2009.

Spectroscopy has been the foundation of many key Hubble discoveries. For example, Hubble has recorded a black hole’s signature, and its spectroscopic observations fingerprinted the distant Universe using the light from quasars to allow astronomers to probe the raw materials from which galaxies form. Using its spectrographs, Hubble has also provided the first direct detection of the atmosphere of a planet orbiting a star outside our Solar System and has detected organic molecules in the atmosphere of a planet orbiting another star.

We invite you to watch this Hubblecast that explores how spectroscopy works and how it facilitates valuable research with the Hubble Space Telescope, including innovative research in the study of exoplanets.

Learn more about Hubble’s observations of gravitational lensing here.