Stellar pulsation

Stellar pulsation is the periodic expansion and contraction of a star’s outer layers, producing changes in its radius, temperature, and luminosity.

κ-mechanism: An opacity-driven process that stores and releases heat in a star’s partially ionized layers, sustaining pulsations. It drives many classical Cepheid and RR Lyrae pulsations by trapping heat during compression.
Cepheid variable: A luminous pulsating star whose period of brightness variation is closely related to its intrinsic luminosity. Its period–luminosity relation makes it a cornerstone of the extragalactic distance scale.
Mira variable: A cool, evolved pulsating star with large-amplitude, long-period changes in visible brightness. Mira stars illustrate how pulsation in an expanded giant can drive strong brightness and radius changes.
Eclipsing binary: A binary star system whose observed brightness changes as one component passes in front of the other. Its periodic dimming comes from changing alignment, not expansion and contraction of a star.
John Goodricke: An English astronomer who identified periodic variability in several stars in the late eighteenth century. His observations of Delta Cephei helped establish the regularity of pulsating-star brightness changes.
Eddington valve: A stellar pulsation mechanism in which opacity changes regulate radiative energy flow and alter pressure in an envelope. This valve analogy explains how compression can increase opacity and strengthen the restoring pressure.
RR Lyrae variable: A low-mass pulsating star with a short, regular period, commonly found in old stellar populations. Its nearly standard luminosity helps measure distances within the Milky Way and nearby galaxies.
Delta Scuti variable: A star showing short-period, low-amplitude pulsations, usually through radial and nonradial modes. Its multiple modes make it a useful case for studying pulsation in intermediate-mass stars.
Rotational variable star: A star whose observed brightness varies as rotation carries spots or other surface features into view. Rotation changes the visible surface pattern without requiring periodic radial motion.
Arthur Eddington: A British astrophysicist who developed foundational theories of stellar structure and pulsation. His work connected stellar opacity and energy transport to the driving of pulsations.

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