Spectra

Astronomy is different from most other sciences in the sense that it relies almost exclusively on the collection and analysis of light from distant sources—a few precious photons from a remote location in the Universe may contain clues to understanding conditions or an event not reproducible in any human-made laboratory.

Most people associate astronomy with awe-inspiring images, but much of astronomical research comes from the analysis of astronomical spectra—light output as a function of color or wavelength. An object’s spectrum is obtained by running its light through a prism or diffraction grating; the result is a “rainbow” with a set of present or missing colors depending on the object’s elemental composition. The spectrum of every element is unique, and like a fingerprint, it can be used to identify an element in an astronomical source.

Spectral lines from various gases. (Palomar/Caltech)

An interactive exhibit in the Greenway Visitor Center allows visitors to learn more about spectra. Tubes containing xenon, mercury, nitrogen, neon, argon, and helium can be lit at will and seen through a grating. The emission spectrum of each gas appears as a unique set of color lines on either side of the tubes.

In addition to chemical composition, spectra are also used in determining an object’s temperature, motion along the line of sight, time-dependent or transient events and variability, exchange of matter (accretion and ejection), presence of convection, presence of companion objects, cosmological distance (in terms of redshift), rotational parameters in galaxies, and much more.