As recently as the 19th century, many people thought that
it would be impossible to determine the chemical composition of
the stars. Since then, astrophysicists have proved them wrong
-- using spectroscopy.
The word 'spectrum' (the plural of which is 'spectra') is used today
to mean 'a display of electromagnetic
radiation as a function
of wavelength.' Spectrum
used to mean 'phantom' or 'apparition', but
introduced a new meaning in 1671, when
he reported his experiment of decomposing the white sunlight into
colors using a prism. Several related words, such as 'spectroscopy'
(the study of spectra)
and 'spectrograph', have since been introduced into the English
You can be a spectroscopist (a person who studies spectra),
too! When you see a rainbow, observe it carefully. Or use a prism on
a beam of sunlight to project a band of colors onto a screen or a
wall. It will probably look to your eyes like the change of colors is
gradual, and the change in intensity of light of different colors is also
gradual. We use the word 'continuum' to describe spectra that change
gradually like this.
There are also discrete features, called
'emission lines' or 'absorption lines' depending on whether they are
brighter or fainter than the neighboring continuum. You can use a
prism on candlelight or some special light bulbs to see such spectral lines.
How do you make a spectrograph?
What do spectra tell us?
What's so special about X-ray and
Use Hera to try your hand at
analyzing spectra with modern data.