Knowra Messier 13 Messier 13 Messier 13 is a dense globular cluster in the constellation Hercules, about 22,000 light-years from Earth. It is among the brightest globular clusters visible from the Northern Hemisphere.
Globular cluster : A roughly spherical, tightly bound collection of old stars orbiting a galaxy. Messier 13 is a classic example of this stellar system.
Gravitation : The attractive interaction between masses, described by general relativity and approximated by Newtonian gravity in weak fields. Gravity keeps Messier 13's stars bound despite their rapid motions.
Edmond Halley : An English astronomer and mathematician who cataloged the object now known as Messier 13 in 1714. Halley's report is the earliest known published notice of the cluster.
Color–magnitude diagram : A plot comparing stars' brightness with their color, used to study stellar populations and evolution. Plotting M13's stars exposes its main sequence, giant branch, and horizontal branch.
Messier 3 : A rich globular cluster in the constellation Canes Venatici, known for its numerous variable stars. Its redder horizontal branch contrasts with M13's notably blue one.
Hercules (constellation) : A large constellation in the northern sky, named for the Greek hero Heracles. Messier 13 lies within Hercules, between the stars Eta and Zeta Herculis.
Stellar dynamics : The study of how stars move and interact under their mutual gravity and a system's overall gravitational field. It explains the cluster's central concentration, orbital motions, and long-term evolution.
Charles Messier : A French astronomer who compiled a catalog of nebulae and star clusters in the eighteenth century. Messier included the cluster as entry 13 in his catalog.
Variable star : A star whose observed brightness changes over time because of intrinsic or extrinsic causes. Pulsating variables in M13 help measure its distance and probe stellar evolution.
Messier 5 : A bright globular cluster in Serpens, among the most prominent clusters in the Northern Hemisphere. Comparing its stellar population with M13 helps illustrate differences among old clusters.
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