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Glossary

This glossary covers words that you will come across on this website.

Spectra

Conditions or values that vary over a continuum. (plural of spectrum)

Spectral line

When an electron makes a transition between two energy levels in an atom, emission or absorption lines arise in a spectrum. A drop to a lower level releases a photon of energy, and a jump to a higher level requires an input of energy.

Spectroscopy

The method of obtaining the spectra of clestial bodies, from which we can determine their composition and motions. Originally it was the study of the interaction between radiation and matter as a function of wavelength.

Spectrum

1. A range of electromagnetic energies arranged in order of wavelength or frequency.

2.The colours produced when visible light passes through a spectroscope.

Spiral galaxy

A spiral galaxy consists of a central bulge of older stars, and a disk of younger stars, arranged in spiral arms, spread out from the central region. In Hubble's classification this is given by the symbol, S.

Synonyms: spiral, spirals
Standard candle

Many methods of measuring interstellar distances rely on a Standard candle, which is an astronomical object that has a known luminosity.

Synonyms: