The Interface Region Imaging Spectrograph (IRIS) is a NASA Small Explorer mission that provides high-resolution spectra and images of the Sun in the 133–141 nm and 278–283 nm wavelength bands.

A short guide to spectroscopy is given, with emphasis upon the elementary physics needed to understand and begin modeling the radiation emerging from astrophysical plasmas using the Sun as a guide, without bias towards a particular region of the Sun's atmosphere.