Caption: A comparison of the spectra obtained by dispersion from a diffraction grating and a prism.

Features:

1. A diffraction grating is just a screen with many finely spaced slits through which light diffracts.

   Diffraction is wavelength-dependent, and so one gets dispersion.

2. A diffraction grating creates a standard diffraction pattern (which could also be called and interference pattern)

   There is a bright central (interference) fringe (as it is called) of all wavelengths (the zeroth order undispersed "spectrum") and then to the left and right are 1st order dispersed dispersed spectra.

   Higher order spectra appear farther to the left and right. The higher the order, the farther the spectra are from the bright central fringe and the dimmer they are.

   As one can see from the figure, with diffraction gratings the shorter the wavelength, less spreading out (i.e., the less the diffraction).

3. A prism creates dispersion by wavelength-dependent refraction.

   As one can see from the figure, with refraction the shorter the wavelength, the greater the angular deviation of the light ray (i.e., the greater the refraction.

4. In practice, diffraction gratings can give much more dispersion than prisms. Thus, diffraction gratings are the main dispersion optical devices used in spectroscopy (i.e., in spectroscopes).

5. There is an optical device that combines a diffraction grating and a prism that is used for special purposes---it's called a grism---which is NOTt named after astronaut Gus Grissom (1926--1967)---who named a star after himself---Navi (γ CAS)---which is his middle name Ivan spelled in reverse---it's an ananym.