The image below shows the solar spectrum at 392 nm (blue)
to 692 nm (red) as observed with the Fourier Transform
Spectrograph at Kitt Peak National Observatory in 1981.
R. Kurucz corrected the
spectrum for absorption from the Earth's atmosphere and made
for public use. The data are shown as if acquired by an echelle
spectrograph, with wavelength increasing from top to bottom and,
within each horizontal row, from left to right. To see an expanded view,
click on the image.
Spectra of the Sun and other stars tell us the composition, density,
and temperature of the stellar atmosphere. Atoms in the atmosphere
absorb light emitted at lower layers and produce the dark vertical
lines or bands in the spectrum. The amount of light removed and the
width of the band are related to the composition, density, and
temperature in the atmosphere.
In addition to providing measurements of the conditions in the stellar
atmosphere, spectra measure the motions of stars. Rapid changes in
the dark lines and bands on time scales of minutes are related to
motions in the stellar atmosphere. The Doppler shift (the difference
between the observed wavelength of the line and its actual wavelength)
tells us the velocity of the star relative to the Earth. By measuring
changes in the relative velocity with time, we can detect the motions
induced by exoplanets or other objects orbiting the star.