Knowra Binary star Binary star A binary star is a system of two stars bound by gravity and orbiting their shared center of mass. Their mutual motion lets astronomers measure stellar masses and study interactions between stars.
Barycenter : The center of mass around which two or more bodies orbit under their mutual gravity. Both stars orbit this shared center, whose position depends on their masses.
Eclipsing binary : A binary star whose orbital plane is aligned so that one star periodically passes in front of the other. Its eclipses constrain stellar sizes, orbital inclination, and, with spectra, masses.
Sirius : The brightest star in Earth's night sky, consisting of the A-type star Sirius A and white dwarf Sirius B. Its visible and white-dwarf components helped establish the reality of stellar remnants.
Optical double star : Two stars that appear close together in the sky but are not gravitationally bound to each other. It can mimic a binary's appearance without sharing its defining mutual orbit.
Kepler's laws of planetary motion : Three laws describing how orbital periods, shapes, and areas relate in gravitational systems. They connect a binary's orbital period and separation to the stars' combined mass.
Spectroscopic binary : A binary star identified through periodic Doppler shifts in one or both stars' spectral lines. Its spectra expose orbital motion even when the stars appear unresolved.
Algol : A multiple-star system whose eclipsing inner pair produces the prototype Algol-type variable star. Its changing brightness made eclipsing binaries recognizable before their geometry was understood.
Multiple star : A gravitationally bound stellar system containing three or more stars, often arranged in nested orbits. It generalizes the two-star system to hierarchical groups with additional components.
Radial velocity : The velocity of an object along the line of sight, measured from shifts in its spectrum. Alternating Doppler shifts reveal each star's motion toward and away from Earth.
Visual binary : A binary star whose two components can be separately resolved and tracked across the sky. Measuring its apparent orbit and distance yields the system's total mass.
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