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Info < Variable Stars < back
A variable star is a star that fluctuates in brightness over a period of time. Some variable stars change from fractions of seconds to years. Variable stars can be put into two basic types - intrinsic and extrinsic.
Intrinsic variable stars changes in brightness due to physical changes in the star themselves. Intrinsic variable stars can then be divided into three main categories.
Extrinsic variable stars change in brightness due to something outside of the star which alters its light, as seen from the Earth. Two main types of extrinsic variable stars are:
Pulsating variables are stars that show periodic expansions and contractions of their surface layers.
*Cepheid Variable Stars
(Period: 1-70 days; Amplitude of variation: .1 to 2.0 mag.)The most important pulsating stars are the Cepheid Variable Stars. The name was derived from the first of their type to be studied, the star Delta in the constellation Cepheus.
*RR Lyrae stars
(Period: 30-100 days; Amplitude of variation: .3 to 2 mag.)These are short-period, pulsating, white giant stars, usually of spectral class A. They are older and less massive than Cepheids.
*RV Tauri stars
(Period: 30-100 days; Amplitude of variation: up to 3.0 mag)These are yellow supergiants having a characteristic light variation with alternating deep and shallow minima.
*Long Period Variables (LPVs)
(Period: 80-1000 days; Amplitude of variation: 2.5 to 5.0 mag.)These are giant red variables that show characteristic emission lines. The spectral classes range through M, C, and S. Also known as “Miras” after the prototype star.
*Semiregular
(Period: 30-1000 days; Amplitude of variation: 1.0 to 2.0 mag.)These are giants and supergiants showing appreciable periodicity accompanied by intervals of irregular light variation.
These are faint, cool, red, main-sequence stars ( red dwarfs ) that undergo intense outbursts from localized areas of the surface. The result is an increase in brightness of two or more magnitudes in several seconds, followed by a decrease to its normal minimum in about 10 to 20 minutes.
Exploding stars (also known as Eruptive or Cataclysmic variables), are stars that have occasional violent outbursts caused by thermonuclear processes either in their surface layers or deep within their interiors. Two main types are Novas and Supernovas.
Eclipsing Binary Stars
These are binary systems of stars with an orbital plane lying near the line-of-sight of the observer. The components periodically eclipse one another, causing a decrease in the apparent brightness of the system as seen by the observer. The period of the eclipse, which coincides with the orbital period of the system, can range from minutes to years.
Rotating Stars
Rotating stars show small changes in light that may be due to dark or bright spots, or patches on their stellar surfaces (“starspots”). Rotating stars are often binary systems.
For more information on Variable Stars please visit the AAVSO website
*Variable Stars - AAVSO: http://www.aavso.org/vstar/
