best spy app for mobile phones apk spy physical location tracker software for android phones mobile call tracker here mobile phone tracking in pakistan cell phone listening software x64 best spyware for galaxy note 3 apps that best cheating spouse business how to remove spyware online cell phone tracker uk here whatsapp spy iphone cydia iphone parental monitoring best spy phone software android press best spy apps for andriod boyfriend spy text messages blackberry spy on your cheating husbands phone call tracker spy is how how spy on phone cell phone listening device iphone iphone spy cam wifi app


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


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.


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.


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.