Asymptotic giant branchThe asymptotic giant branch (AGB) is a region of the Hertzsprung–Russell diagram populated by evolved cool luminous stars. This is a period of stellar evolution undertaken by all low- to intermediate-mass stars (about 0.5 to 8 solar masses) late in their lives. Observationally, an asymptotic-giant-branch star will appear as a bright red giant with a luminosity ranging up to thousands of times greater than the Sun.
Giant starHertzsprung–Russell diagramSpectral typeOBAFGKMLTBrown dwarfsWhite dwarfsRed dwarfsSubdwarfsMain sequence("dwarfs")SubgiantsGiantsRed giantsBlue giantsBright giantsSupergiantsRed supergiantHypergiantsabsolutemagni-tude(MV)A giant star has a substantially larger radius and luminosity than a main-sequence (or dwarf) star of the same surface temperature.SubgiantHertzsprung–Russell diagramSpectral typeOBAFGKMLTBrown dwarfsWhite dwarfsRed dwarfsSubdwarfsMain sequence("dwarfs")SubgiantsGiantsRed giantsBlue giantsBright giantsSupergiantsRed supergiantHypergiantsabsolutemagni-tude(MV)A subgiant is a star that is brighter than a normal main-sequence star of the same spectral class, but not as bright as giant stars. The term subgiant is applied both to a particular spectral luminosity class and to a stage in the evolution of a star.Red giantHertzsprung–Russell diagramSpectral typeOBAFGKMLTBrown dwarfsWhite dwarfsRed dwarfsSubdwarfsMain sequence("dwarfs")SubgiantsGiantsRed giantsBlue giantsBright giantsSupergiantsRed supergiantHypergiantsabsolutemagni-tude(MV)A red giant is a luminous giant star of low or intermediate mass (roughly 0.3–8 solar masses (M☉)) in a late phase of stellar evolution.
Stellar evolutionStellar evolution is the process by which a star changes over the course of time. Depending on the mass of the star, its lifetime can range from a few million years for the most massive to trillions of years for the least massive, which is considerably longer than the current age of the universe. The table shows the lifetimes of stars as a function of their masses. All stars are formed from collapsing clouds of gas and dust, often called nebulae or molecular clouds.
Variable starStar whose brightness fluctuates, as seen from EarthComparison of VLT-SPHERE images of Betelgeuse taken in January 2019 and December 2019, showing the changes in brightness and shape. Betelgeuse is an intrinsically variable star.A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes systematically with time.
Main sequenceA Hertzsprung–Russell diagram plots the luminosity (or absolute magnitude) of a star against its color index (represented as B−V). The main sequence is visible as a prominent diagonal band from upper left to lower right.Hertzsprung–Russell diagramA Hertzsprung–Russell diagram (abbreviated as H–R diagram, HR diagram or HRD) is a scatter plot of stars showing the relationship between the stars' absolute magnitudes or luminosities and their stellar classifications or effective temperatures. It is also sometimes called a color magnitude diagram.
White dwarfA white dwarf is a very dense type of star: in an Earth-sized volume, it packs a mass that is comparable to the Sun. A white dwarf radiates light from residual heat and eventual crystallization, not from nuclear fusion. Stars like the Sun, whose mass is not high enough to collapse into a neutron star or black hole, are expected to become white dwarf stars later in their evolution.
HeliumChemical element with atomic number 2 (He)–↑He↓Nehydrogen ← helium → lithium
CNO cycleIn astrophysics, the carbon–nitrogen–oxygen cycle (CNO cycle), sometimes called Bethe–Weizsäcker cycle after Hans Albrecht Bethe and Carl Friedrich von Weizsäcker, is one of the two known sets of fusionreactions by which stars convert hydrogen to helium, the other being the proton–proton chain reaction (p–p chain), which is more efficient at the Sun's core temperature.
HydrogenChemical element with atomic number 1 (H)–↑H↓Li(none) ← hydrogen → helium*As an Amazon Associate I earn from qualifying purchases.