Spectra
Every object has its own spectrum that depends on what it is made of. The plural of spectrum is `spectra'. We try to understand why the Sun's spectrum looks as it does. If we tried to measure the complete Solar spectrum from radio waves to gamma waves , different telescopes would be needed.

There are three main features seen in spectra:

  1. A continuous background (called continuum)
  2. Emission lines
  3. Absorption lines

The background light is smooth, called the continuum.

In an atom, the electrons orbit around the nucleus at set distances. They cannot go anywhere they like. When an electron jumps to a smaller orbit it gives out a photon of radiation, an emission line.

When an electron wants to go from a smaller orbit to a larger one, it needs energy. It takes energy away from the light which is passing through it - so we see an absorption line.

Did you know? The element Helium was discovered using the light from the Sun (and was named after the Greek Sun God). At the time, in 1868, there was no known material on Earth which could produce a spectral line at the same wavelength. Helium was finally discovered on Earth some 30 years later.

Here is a spectrum from SOHO showing an emission line spectrum from the corona in the ultraviolet

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