The Space Telescope Imaging Spectrograph (STIS) was installed on Hubble during Servicing Mission 2 in 1997, replacing the Goddard High Resolution Spectrograph (GHRS). This second generation spectrograph was developed under the direction of the principal investigator, Dr. Bruce E. Woodgate, NASA GSFC, jointly with Ball Aerospace.

A spectrograph is an instrument that uses optical elements called gratings or prisms, to separate the light gathered by the telescope into its component colors or wavelengths. A spectrograph spreads out the light gathered by a telescope so that it can be analyzed in order to find out many different things about celestial objects; they include the chemical composition and abundance of different elements, temperature, radial velocity, rotational velocity, and magnetic fields.

A key feature of STIS is its ability to produce two-dimensional spectroscopy, determining the spectrum of spatially extended objects, such as galaxies, covering many points across the image simultaneously, up to 512 points. This affords the astronomers the opportunity to gather more data in less time, enabling many new scientific discoveries that previously were hopeless to pursue because the process was so time consuming.

The instrument is sensitive to a wide range of wavelengths of light, spanning from the vacuum, far-ultraviolet (FUV) (115 nm) through the optical to the near infrared (NIR) (1000 nm).

The STIS can be switched between two primary modes of usage:

• Long Slit Spectroscopy - where spectra of many different points across an object are obtained simultaneously
  
  
• Echelle Spectroscopy - where the spectrum of one object is spread over the detector giving better wavelength resolution in a single exposure

STIS also possesses a coronagraph (example below) which can block light from a bright object, enabling investigations of its surrounding material and nearby fainter objects. It can be thought of as a simulation of a total eclipse on a nearby star.

STIS possesses a limited filter set supporting imaging but, its heart is spectroscopy, which is enabled by a diverse set of gratings ahead of the detectors in the optical chain. A grating, functionally similar to a prism, creates a spectrum by separating light into its individual wavelength components. Although spectrographs generally do not produce beautiful images like Hubble's cameras, the data they provide are absolutely essential to understanding the physical properties of the material universe - they put the "physics" in astrophysics.

More detailed information can be found on the STIS website at the Space Telescope Science Institute (http://www.stsci.edu/hst/stis).