Astrophysics (Index)About

variable star

(star that varies in magnitude)

A variable star (or just a variable) is a star which becomes dimmer and brighter over time as seen from Earth. This can be due to changes in the star such as brightening or enlarging, or through a change in whatever the light must pass through to reach us. Examples: Achernar, AD Leonis, Algol, DQ Tau, GG Tau, HL Tau, Lalande 21185, Rigel, Ross 154, Ross 248, T Tauri, Vega.

Stars generally are at least slightly variable, such as the 0.1% variability of the Sun over the solar cycle. The term microvariable indicates a star showing very slight variability, e.g., small enough that multiple observations must be made to preclude instrument variability and random errors. The term rotational modulation indicates the repeating pattern of variability that is a signature of starspots. Some general classes:

Variation may be something that occurs in less than the course of a day (intraday variable or IDV) or for some pulsating stars, a variation period longer than 30 or so days (a long period variable or LPV) or even over spans of years such as FU Orionis stars.

Some of the specific types:

The details of the observed variation offer clues to the sources of variation, often revealing or confirming models of stellar structure for the given star, for its particular variable-star type, and for stars in general. In this sense, variable stars are analogous to binary stars, which also serve as windows into stellar detail.

(star type,transient type,variable)
Further reading:

Referenced by pages:
AB Pictoris (AB Pic)
AD Leonis (AD Leo)
asymptotic giant branch (AGB)
Algol (Beta Per)
amateur astronomy
AU Microscopii (AU Mic)
Bibliographic Catalog of Variable Stars (BCVS)
Beta Centauri
Cepheid variable (CEP)
contact binary
cataclysmic variable star (CV)
eclipsing binary (E)
Frank Ross's Catalog (Ross)
FU Orionis star (FUor)
General Catalogue of Variable Stars (GCVS)
helium star
Herbig AeBe star (HAeBe)
Hubble constant (H0)
Hubble expansion
instability strip
kappa mechanism (κ-mechanism)
KIC 8462852
Lalande 21185
luminous blue variable (LBV)
LaSilla-QUEST Variability Survey (LSQ)
Messier 15 (M15)
MACHO Project
main sequence star (MS)
mass transfer
New Catalogue of Suspected Variable Stars (NSV)
partial ionization zone
planetary nebula (PN)
pulsating star
rare designator prefixes
Ross 154
Ross 248
RR Lyrae variable (RRL)
shell star (sh)
spectral type
stellar designation
transient astronomy
T Tauri
T-Tauri star (TTS)
variable star designation
Whole Earth Telescope (WET)