The Formation of Stellar Spectra
A normal star is a huge ball of gas compressed by its own gravity.
The gas is dense enough to keep an energy producing nucleosynthesis
alive in its core. This nucleosynthesis works at a temperature above
10 million Kelvin. It produces a pressure pointing outside against the
direction of gravity. And it makes the star shine.
The stellar spectra consist of two components. The continuum
and absorption lines.
Sometimes there are lines in
emission. The major source of light is the continuum.
Hot
solids, liquids and very dense gases emit a continuous
spectrum.
Here we can assign a number to every color in our
spectrum.
Move the mouse over the image to see
these numbers, called wavelengths.
A gas can emit light if it is hot enough or it is excited in an other
way. The spectrum is not a continuum but consists of a typical set of
wavelenghts. Each chemical element has its own set of emission
lines.
If we look through a cool gas onto a hot survey emitting a continuum we can see
the spectral lines corresponding to the elements in the gaseous layer in
absorption. The gas is cooler than the hot survey, so it emits less light at its
own wavelengths.
The three spectra on this page are used with the kind
permission of the Armagh Observatory.