Knowra Mira variable Mira variable A Mira variable is a pulsating red giant whose brightness changes greatly over a regular cycle, usually lasting several months to more than a year. Its long-period pulsations and cool atmosphere distinguish it from other variable stars.
Stellar pulsation : Periodic expansion and contraction of a star driven by internal physical processes. Mira variables brighten and fade as their outer layers expand and contract.
Red giant : A luminous, expanded star that has exhausted hydrogen in its core and evolved beyond the main sequence. Mira variables are cool, expanded red giants in a late stage of stellar evolution.
Mira : A pulsating red giant in Cetus, also known as Omicron Ceti, and the prototype of Mira variables. This star gave the class its name after its changing brightness drew sustained attention.
Semiregular variable star : A pulsating giant or supergiant whose brightness changes with less regularity than a Mira variable. Semiregular variables have less predictable cycles and generally smaller brightness changes.
κ-mechanism : A pulsation-driving process in which increased opacity traps heat and helps sustain stellar oscillations. Opacity changes in ionized helium help power the radial pulsations of many Mira stars.
Asymptotic giant branch : A late evolutionary phase of low- and intermediate-mass stars, with hydrogen- and helium-burning shells. Most Mira variables are asymptotic-giant-branch stars nearing the end of their evolution.
Chi Cygni : A long-period variable star in Cygnus whose visible brightness varies dramatically. Its large, well-observed cycles provide a prominent example of Mira-like variability.
Classical Cepheid variable : A luminous, radially pulsating supergiant whose period is tightly related to its luminosity. Cepheids are generally hotter and more massive, with shorter, more regular cycles.
Stellar atmosphere : The outer gaseous layers of a star, from its photosphere to its outer boundary. Pulsation-driven temperature and opacity changes in this layer alter visible brightness.
Stellar magnitude : A logarithmic scale for expressing the apparent or intrinsic brightness of celestial objects. A Mira’s large amplitude is measured as a substantial change in magnitude.
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