A planetary system is a set of gravitationally bound non-stellar objects in or out of orbit around a star or star system. Generally speaking, systems with one or more planets constitute a planetary system, although such systems may also consist of bodies such as dwarf planets, asteroids, natural satellites, meteoroids, comets, planetesimals[1][2] and circumstellar disks. The Sun together with the planets revolving around it, including Earth, is known as the Solar System.[3][4] The term exoplanetary system is sometimes used in reference to other planetary systems.

As of 1 December 2020, there are 4,379 confirmed exoplanets in 3,237 systems, with 717 systems having more than one planet.[5] Debris disks are also known to be common, though other objects are more difficult to observe.

Of particular interest to astrobiology is the habitable zone of planetary systems where planets could have surface liquid water, and thus the capacity to harbor Earth-like life.


Historically, heliocentrism (the doctrine that the Sun is at the centre of the universe) was opposed to geocentrism (placing the Earth at the center of the universe).

The notion of a heliocentric Solar System, with the Sun at the center, is possibly first suggested in the Vedic literature of ancient India, which often refer to the Sun as the "centre of spheres". Some interpret Aryabhatta's writings in Āryabhaṭīya as implicitly heliocentric.

The idea was first proposed in Western philosophy and Greek astronomy as early as the 3rd century BC by Aristarchus of Samos,[6] but received no support from most other ancient astronomers.
Discovery of the Solar System
Main article: Discovery and exploration of the Solar System
Heliocentric model of the Solar System in Copernicus' manuscript

De revolutionibus orbium coelestium by Nicolaus Copernicus, published in 1543, presented the first mathematically predictive heliocentric model of a planetary system. 17th-century successors Galileo Galilei, Johannes Kepler, and Sir Isaac Newton developed an understanding of physics which led to the gradual acceptance of the idea that the Earth moves round the Sun and that the planets are governed by the same physical laws that governed the Earth.
Speculation on extrasolar planetary systems

In the 16th century the Italian philosopher Giordano Bruno, an early supporter of the Copernican theory that the Earth and other planets orbit the Sun, put forward the view that the fixed stars are similar to the Sun and are likewise accompanied by planets. He was burned at the stake for his ideas by the Roman Inquisition.[7]

In the 18th century the same possibility was mentioned by Sir Isaac Newton in the "General Scholium" that concludes his Principia. Making a comparison to the Sun's planets, he wrote "And if the fixed stars are the centers of similar systems, they will all be constructed according to a similar design and subject to the dominion of One."[8]

His theories gained traction through the 19th and 20th centuries despite a lack of supporting evidence. Long before their confirmation by astronomers, conjecture on the nature of planetary systems had been a focus of the search for extraterrestrial intelligence and has been a prevalent theme in fiction, particularly science fiction.
Detection of exoplanets

The first confirmed detection of an exoplanet was in 1992, with the discovery of several terrestrial-mass planets orbiting the pulsar PSR B1257+12. The first confirmed detection of exoplanets of a main-sequence star was made in 1995, when a giant planet, 51 Pegasi b, was found in a four-day orbit around the nearby G-type star 51 Pegasi. The frequency of detections has increased since then, particularly through advancements in methods of detecting extrasolar planets and dedicated planet finding programs such as the Kepler mission.
Origin and evolution
See also: Nebular hypothesis, Planetary migration, and Formation and evolution of the Solar System
An artist's concept of a protoplanetary disk

Planetary systems come from protoplanetary disks that form around stars as part of the process of star formation.

During formation of a system much material is gravitationally scattered into far-flung orbits and some planets are ejected completely from the system becoming rogue planets.
Evolved systems
High-mass stars

Planets orbiting pulsars have been discovered. Pulsars are the remnants of the supernova explosions of high-mass stars, but a planetary system that existed before the supernova would likely be mostly destroyed. Planets would either evaporate, be pushed off of their orbits by the masses of gas from the exploding star, or the sudden loss of most of the mass of the central star would see them escape the gravitational hold of the star, or in some cases the supernova would kick the pulsar itself out of the system at high velocity so any planets that had survived the explosion would be left behind as free-floating objects. Planets found around pulsars may have formed as a result of pre-existing stellar companions that were almost entirely evaporated by the supernova blast, leaving behind planet-sized bodies. Alternatively, planets may form in an accretion disk of fallback matter surrounding a pulsar.[9] Fallback disks of matter that failed to escape orbit during a supernova may also form planets around black holes.[10]
Lower-mass stars
Protoplanetary discs observed with the Very Large Telescope.[11]

As stars evolve and turn into red giants, asymptotic giant branch stars, and planetary nebulae they engulf the inner planets, evaporating or partially evaporating them depending on how massive they are. As the star loses mass, planets that are not engulfed move further out from the star.

If an evolved star is in a binary or multiple system then the mass it loses can transfer to another star, creating new protoplanetary disks and second- and third-generation planets which may differ in composition from the original planets which may also be affected by the mass transfer.

Planets in evolved binary systems, Hagai B. Perets, January 13, 2011
Can Planets survive Stellar Evolution?, Eva Villaver, Mario Livio, Feb 2007
The Orbital Evolution of Gas Giant Planets around Giant Stars, Eva Villaver, Mario Livio, October 13, 2009
On the survival of brown dwarfs and planets engulfed by their giant host star, Jean-Claude Passy, Mordecai-Mark Mac Low, Orsola De Marco, October 2, 2012
Foretellings of Ragnarök: World-engulfing Asymptotic Giants and the Inheritance of White Dwarfs, Alexander James Mustill, Eva Villaver, December 5, 2012

System architectures

The Solar System consists of an inner region of small rocky planets and outer region of large gas giants. However, other planetary systems can have quite different architectures. Studies suggest that architectures of planetary systems are dependent on the conditions of their initial formation.[12] Many systems with a hot Jupiter gas giant very close to the star have been found. Theories, such as planetary migration or scattering, have been proposed for the formation of large planets close to their parent stars.[13] At present, few systems have been found to be analogous to the Solar System with terrestrial planets close to the parent star. More commonly, systems consisting of multiple Super-Earths have been detected.[14]
Planets and stars
Main article: Planet-hosting stars
The Morgan-Keenan spectral classification

Most known exoplanets orbit stars roughly similar to the Sun, that is, main-sequence stars of spectral categories F, G, or K. One reason is that planet-search programs have tended to concentrate on such stars. In addition, statistical analyses indicate that lower-mass stars (red dwarfs, of spectral category M) are less likely to have planets massive enough to be detected by the radial-velocity method.[15][16] Nevertheless, several tens of planets around red dwarfs have been discovered by the Kepler spacecraft by the transit method, which can detect smaller planets.
Circumstellar disks and dust structures
Main article: circumstellar disk
Debris disks detected in HST archival images of young stars, HD 141943 and HD 191089, using improved imaging processes (April 24, 2014).

After planets, circumstellar disks are one of the most commonly observed properties of planetary systems, particularly of young stars. The Solar System possesses at least four major circumstellar disks (the asteroid belt, Kuiper belt, scattered disc, and Oort cloud) and clearly observable disks have been detected around nearby solar analogs including Epsilon Eridani and Tau Ceti. Based on observations of numerous similar disks, they are assumed to be quite common attributes of stars on the main sequence.

Interplanetary dust clouds have been studied in the Solar System and analogs are believed to be present in other planetary systems. Exozodiacal dust, an exoplanetary analog of zodiacal dust, the 1–100 micrometre-sized grains of amorphous carbon and silicate dust that fill the plane of the Solar System[17] has been detected around the 51 Ophiuchi, Fomalhaut,[18][19] Tau Ceti,[19][20] and Vega systems.
Main article: Comet

As of November 2014 there are 5,253 known Solar System comets[21] and they are thought to be common components of planetary systems. The first exocomets were detected in 1987[22][23] around Beta Pictoris, a very young A-type main-sequence star. There are now a total of 11 stars around which the presence of exocomets have been observed or suspected.[24][25][26][27] All discovered exocometary systems (Beta Pictoris, HR 10,[24] 51 Ophiuchi, HR 2174,[25] 49 Ceti, 5 Vulpeculae, 2 Andromedae, HD 21620, HD 42111, HD 110411,[26][28] and more recently HD 172555[27]) are around very young A-type stars.
Other components
Further information: Circumplanetary disk

Computer modelling of an impact in 2013 detected around the star NGC 2547-ID8 by the Spitzer Space Telescope and confirmed by ground observations suggests the involvement of large asteroids or protoplanets similar to the events believed to have led to the formation of terrestrial planets like the Earth.[29]

Based on observations of the Solar System's large collection of natural satellites, they are believed common components of planetary systems; however, exomoons have so far eluded confirmation. The star 1SWASP J140747.93-394542.6, in the constellation Centaurus, is a strong candidate for a natural satellite.[30] Indications suggest that the confirmed extrasolar planet WASP-12b also has at least one satellite.[31]
Orbital configurations

Unlike the Solar System, which has orbits that are nearly circular, many of the known planetary systems display much higher orbital eccentricity.[32] An example of such a system is 16 Cygni.
Mutual inclination

The mutual inclination between two planets is the angle between their orbital planes. Many compact systems with multiple close-in planets interior to the equivalent orbit of Venus are expected to have very low mutual inclinations, so the system (at least the close-in part) would be even flatter than the solar system. Captured planets could be captured into any arbitrary angle to the rest of the system. As of 2016 there are only a few systems where mutual inclinations have actually been measured[33] One example is the Upsilon Andromedae system: the planets, c and d, have a mutual inclination of about 30 degrees.[34][35]
Orbital dynamics

Planetary systems can be categorized according to their orbital dynamics as resonant, non-resonant-interacting, hierarchical, or some combination of these. In resonant systems the orbital periods of the planets are in integer ratios. The Kepler-223 system contains four planets in an 8:6:4:3 orbital resonance.[36] Giant planets are found in mean-motion resonances more often than smaller planets.[37] In interacting systems the planets orbits are close enough together that they perturb the orbital parameters. The Solar System could be described as weakly interacting. In strongly interacting systems Kepler's laws do not hold.[38] In hierarchical systems the planets are arranged so that the system can be gravitationally considered as a nested system of two-bodies, e.g. in a star with a close-in hot jupiter with another gas giant much further out, the star and hot jupiter form a pair that appears as a single object to another planet that is far enough out.

Other, as yet unobserved, orbital possibilities include: double planets; various co-orbital planets such as quasi-satellites, trojans and exchange orbits; and interlocking orbits maintained by precessing orbital planes.[39]

Extrasolar Binary Planets I: Formation by tidal capture during planet-planet scattering, H. Ochiai, M. Nagasawa, S. Ida, June 26, 2014
Disruption of co-orbital (1:1) planetary resonances during gas-driven orbital migration, Arnaud Pierens, Sean Raymond, May 19, 2014

Number of planets, relative parameters and spacings
The spacings between orbits vary widely amongst the different systems discovered by the Kepler spacecraft.

On The Relative Sizes of Planets Within Kepler Multiple Candidate Systems, David R. Ciardi et al. December 9, 2012
The Kepler Dichotomy among the M Dwarfs: Half of Systems Contain Five or More Coplanar Planets, Sarah Ballard, John Asher Johnson, October 15, 2014
Exoplanet Predictions Based on the Generalised Titius-Bode Relation, Timothy Bovaird, Charles H. Lineweaver, August 1, 2013
The Solar System and the Exoplanet Orbital Eccentricity - Multiplicity Relation, Mary Anne Limbach, Edwin L. Turner, April 9, 2014
The period ratio distribution of Kepler's candidate multiplanet systems, Jason H. Steffen, Jason A. Hwang, September 11, 2014
Are Planetary Systems Filled to Capacity? A Study Based on Kepler Results, Julia Fang, Jean-Luc Margot, February 28, 2013

Planet capture

Free-floating planets in open clusters have similar velocities to the stars and so can be recaptured. They are typically captured into wide orbits between 100 and 105 AU. The capture efficiency decreases with increasing cluster size, and for a given cluster size it increases with the host/primary mass. It is almost independent of the planetary mass. Single and multiple planets could be captured into arbitrary unaligned orbits, non-coplanar with each other or with the stellar host spin, or pre-existing planetary system. Some planet–host metallicity correlation may still exist due to the common origin of the stars from the same cluster. Planets would be unlikely to be captured around neutron stars because these are likely to be ejected from the cluster by a pulsar kick when they form. Planets could even be captured around other planets to form free-floating planet binaries. After the cluster has dispersed some of the captured planets with orbits larger than 106 AU would be slowly disrupted by the galactic tide and likely become free-floating again through encounters with other field stars or giant molecular clouds.[40]
Habitable zone
Main article: Circumstellar habitable zone
Location of habitable zone around different types of stars

The habitable zone around a star is the region where the temperature is just right to allow liquid water to exist on a planet; that is, not too close to the star for the water to evaporate and not too far away from the star for the water to freeze. The heat produced by stars varies depending on the size and age of the star so that the habitable zone can be at different distances. Also, the atmospheric conditions on the planet influence the planet's ability to retain heat so that the location of the habitable zone is also specific to each type of planet.

Habitable zones have usually been defined in terms of surface temperature; however, over half of Earth's biomass is from subsurface microbes,[41] and the temperature increases as one goes deeper underground, so the subsurface can be conducive for life when the surface is frozen and if this is considered, the habitable zone extends much further from the star.[42]

Studies in 2013 indicated an estimated frequency of 22±8% of Sun-like[a] stars have an Earth-sized[b] planet in the habitable[c] zone.[43][44]
Venus zone

The Venus zone is the region around a star where a terrestrial planet would have runaway greenhouse conditions like Venus, but not so near the star that the atmosphere completely evaporates. As with the habitable zone, the location of the Venus zone depends on several factors, including the type of star and properties of the planets such as mass, rotation rate, and atmospheric clouds. Studies of the Kepler spacecraft data indicate that 32% of red dwarfs have potentially Venus-like planets based on planet size and distance from star, rising to 45% for K-type and G-type stars.[d] Several candidates have been identified, but spectroscopic follow-up studies of their atmospheres are required to determine whether they are like Venus.[45][46]
Galactic distribution of planets
See also: Galactic habitable zone, Extragalactic planet, and Globular cluster § Planets
90% of planets with known distances lie within about 2000 light years of Earth, as of July 2014.

The Milky Way is 100,000 light-years across, but 90% of planets with known distances lie within about 2000 light years of Earth, as of July 2014. One method that can detect planets much further away is microlensing. The WFIRST spacecraft could use microlensing to measure the relative frequency of planets in the galactic bulge vs. galactic disk.[47] So far, the indications are that planets are more common in the disk than the bulge.[48] Estimates of the distance of microlensing events is difficult: the first planet considered with high probability of being in the bulge is MOA-2011-BLG-293Lb at a distance of 7.7 kiloparsecs (about 25,000 light years).[49]

Population I, or metal-rich stars, are those young stars whose metallicity is highest. The high metallicity of population I stars makes them more likely to possess planetary systems than older populations, because planets form by the accretion of metals. The Sun is an example of a metal-rich star. These are common in the spiral arms of the Milky Way. Generally, the youngest stars, the extreme population I, are found farther in and intermediate population I stars are farther out, etc. The Sun is considered an intermediate population I star. Population I stars have regular elliptical orbits around the Galactic Center, with a low relative velocity.[50]

Population II, or metal-poor stars, are those with relatively low metallicity which can have hundreds (e.g. BD +17° 3248) or thousands (e.g. Sneden's Star) times less metallicity than the Sun. These objects formed during an earlier time of the universe. Intermediate population II stars are common in the bulge near the center of the Milky Way, whereas Population II stars found in the galactic halo are older and thus more metal-poor. Globular clusters also contain high numbers of population II stars.[51] In 2014 the first planets around a halo star were announced around Kapteyn's star, the nearest halo star to Earth, around 13 light years away. However, later research suggests that Kapteyn b is just an artefact of stellar activity and that Kapteyn c needs more study to be confirmed.[52] The metallicity of Kapteyn's star is estimated to be about 8[e] times less than the Sun.[53]

Different types of galaxies have different histories of star formation and hence planet formation. Planet formation is affected by the ages, metallicities, and orbits of stellar populations within a galaxy. Distribution of stellar populations within a galaxy varies between the different types of galaxies.[54] Stars in elliptical galaxies are much older than stars in spiral galaxies. Most elliptical galaxies contain mainly low-mass stars, with minimal star-formation activity.[55] The distribution of the different types of galaxies in the universe depends on their location within galaxy clusters, with elliptical galaxies found mostly close to their centers.[56]
See also

iconStar portal

Protoplanetary disk
List of exoplanets
List of multiplanetary systems
List of exoplanetary host stars


For the purpose of this 1 in 5 statistic, "Sun-like" means G-type star. Data for Sun-like stars were not available so this statistic is an extrapolation from data about K-type stars
For the purpose of this 1 in 5 statistic, Earth-sized means 1–2 Earth radii
For the purpose of this 1 in 5 statistic, "habitable zone" means the region with 0.25 to 4 times Earth's stellar flux (corresponding to 0.5–2 AU for the Sun).
For the purpose of this, terrestrial-sized means 0.5–1.4 Earth radii, the "Venus zone" means the region with approximately 1 to 25 times Earth's stellar flux for M and K-type stars and approximately 1.1 to 25 times Earth's stellar flux for G-type stars.

Metallicity of Kapteyn's star estimated at [Fe/H]= −0.89. 10−0.89 ≈ 1/8

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Habitable Zone Gallery - Venus
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Stellar activity mimics a habitable-zone planet around Kapteyn's star, Paul Robertson (1 and 2), Arpita Roy (1 and 2 and 3), Suvrath Mahadevan (1 and 2 and 3) ((1) Dept. of Astronomy and Astrophysics, Penn State University, (2) Center for Exoplanets & Habitable Worlds, Penn State University, (3) The Penn State Astrobiology Research Center), (Submitted on May 11, 2015 (v1), last revised June 1, 2015 (this version, v2))
Two planets around Kapteyn's star : a cold and a temperate super-Earth orbiting the nearest halo red-dwarf, Guillem Anglada-Escudé, Pamela Arriagada, Mikko Tuomi, Mathias Zechmeister, James S. Jenkins, Aviv Ofir, Stefan Dreizler, Enrico Gerlach, Chris J. Marvin, Ansgar Reiners, Sandra V. Jeffers, R. Paul Butler, Steven S. Vogt, Pedro J. Amado, Cristina Rodríguez-López, Zaira M. Berdiñas, Julian Morin, Jeff D. Crane, Stephen A. Shectman, Ian B. Thompson, Mateo Díaz, Eugenio Rivera, Luis F. Sarmiento, Hugh R.A. Jones, (Submitted on June 3, 2014)
Habitable Zones in the Universe, G. Gonzalez, (Submitted on March 14, 2005 (v1), last revised March 21, 2005 (this version, v2))
John, D, (2006), Astronomy, ISBN 1-4054-6314-7, p. 224-225

Dressler, A. (March 1980). "Galaxy morphology in rich clusters - Implications for the formation and evolution of galaxies". The Astrophysical Journal. 236: 351–365. Bibcode:1980ApJ...236..351D. doi:10.1086/157753.

Further reading

On the Relationship Between Debris Disks and Planets, Ágnes Kóspál, David R. Ardila, Attila Moór, Péter Ábrahám, June 30, 2009
Signatures of exosolar planets in dust debris disks, Leonid M. Ozernoy, Nick N. Gorkavyi, John C. Mather, Tanya Taidakova, July 4, 2000



IAU Planetary science

Main topics

Exoplanet Methods of detecting exoplanets Planetary system Planet-hosting stars

PDS 70.jpg
and types

Carbon planet Coreless planet Desert planet Dwarf planet Ice planet Iron planet Lava planet Ocean planet Mega-Earth Sub-Earth Super-Earth


Eccentric Jupiter Gas dwarf Helium planet Hot Jupiter Hot Neptune Ice giant Mini-Neptune Super-Neptune Super-Jupiter Super-puff Ultra-hot Jupiter Ultra-hot Neptune

Other types

Blanet Brown dwarf Chthonian planet Circumbinary planet Disrupted planet Double planet Eyeball planet Giant planet Mesoplanet Planemo Planet/Brown dwarf boundary Planetesimal Protoplanet Pulsar planet Sub-brown dwarf Sub-Neptune Ultra-cool dwarf Ultra-short period planet (USP)

and evolution

Accretion Accretion disk Asteroid belt Circumplanetary disk Circumstellar disc Circumstellar envelope Cosmic dust Debris disk Detached object Disrupted planet Excretion disk Exoplanetary Circumstellar Environments and Disk Explorer Exozodiacal dust Extraterrestrial materials Extraterrestrial sample curation Giant-impact hypothesis Gravitational collapse Hills cloud Interplanetary dust cloud Interplanetary medium Interplanetary space Interstellar cloud Interstellar dust Interstellar medium Interstellar space Kuiper belt List of interstellar and circumstellar molecules Merging stars Molecular cloud Nebular hypothesis Oort cloud Outer space Planetary migration Planetary system Planetesimal Planet formation Protoplanetary disk Ring system Rubble pile Sample-return mission Scattered disc Star formation


Interstellar Exomoon
Tidally detached Exoplanet
Rogue planet Retrograde Trojan Mean-motion resonances Titius–Bode laws

Host stars

A B Binary star Brown dwarfs F/Yellow-white dwarfs G/Yellow dwarfs Herbig Ae/Be K/Orange dwarfs M/Red dwarfs Pulsar Red giant Subdwarf B Subgiant T Tauri White dwarfs Yellow giants


Astrometry Direct imaging
list Microlensing
list Polarimetry Pulsar timing
list Radial velocity
list Transit method
list Transit-timing variation


Astrobiology Circumstellar habitable zone Earth analog Extraterrestrial liquid water Habitability of natural satellites Superhabitable planet


Nearby Habitable Systems Exoplanet Data Explorer Extrasolar Planets Encyclopaedia NASA Exoplanet Archive NASA Star and Exoplanet Database


Exoplanetary systems
Host stars Multiplanetary systems Stars with proplyds

Lists Discoveries Extremes Firsts Nearest Largest Most massive Terrestrial candidates Kepler Potentially habitable Proper names

Discovered exoplanets by year
before 2000 2000–2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020


Carl Sagan Institute Exoplanet naming convention Exoplanet phase curves Extragalactic planet Fulton gap Geodynamics of terrestrial exoplanets Neptunian Desert Nexus for Exoplanet System Science Planets in globular clusters Planets in science fiction Sudarsky's gas giant classification

Discoveries of exoplanets Search projects


Stellar systems

Galaxy Dwarf galaxy Star cluster
Globular cluster Dark globular cluster Open cluster Hypercompact stellar system Star system Binary star Planetary system


Stellar stream Stellar association Moving group Runaway star Hypervelocity star

Visual grouping

Double star Multiple star Star cloud Asterism Constellation

Category Category:Star systems


Systems science

Anatomical Art Biological Complex Complex adaptive Conceptual Coupled human–environment Database Dynamical Ecological Economic Energy Formal Holarchic Information Legal Measurement Metric Multi-agent Nervous Nonlinear Operating Physical Planetary Political Sensory Social Star Writing


Doubling time Leverage points Limiting factor Negative feedback Positive feedback


Chaos theory Complex systems Control theory Cybernetics Earth system science Living systems Sociotechnical system Systemics Urban metabolism World-systems theory

Analysis Biology Dynamics Ecology Engineering Neuroscience Pharmacology Psychology Theory Thinking


Alexander Bogdanov Russell L. Ackoff William Ross Ashby Ruzena Bajcsy Béla H. Bánáthy Gregory Bateson Anthony Stafford Beer Richard E. Bellman Ludwig von Bertalanffy Margaret Boden Kenneth E. Boulding Murray Bowen Kathleen Carley Mary Cartwright C. West Churchman Manfred Clynes George Dantzig Edsger W. Dijkstra Fred Emery Heinz von Foerster Stephanie Forrest Jay Wright Forrester Barbara Grosz Charles A. S. Hall Mike Jackson Lydia Kavraki James J. Kay Faina M. Kirillova George Klir Allenna Leonard Edward Norton Lorenz Niklas Luhmann Humberto Maturana Margaret Mead Donella Meadows Mihajlo D. Mesarovic James Grier Miller Radhika Nagpal Howard T. Odum Talcott Parsons Ilya Prigogine Qian Xuesen Anatol Rapoport John Seddon Peter Senge Claude Shannon Katia Sycara Eric Trist Francisco Varela Manuela M. Veloso Kevin Warwick Norbert Wiener Jennifer Wilby Anthony Wilden


Systems theory in anthropology Systems theory in archaeology Systems theory in political science


List Principia Cybernetica

Category Category Portal Portal Commons page Commons



Accretion Molecular cloud Bok globule Young stellar object
Protostar Pre-main-sequence Herbig Ae/Be T Tauri FU Orionis Herbig–Haro object Hayashi track Henyey track


Main sequence Red-giant branch Horizontal branch
Red clump Asymptotic giant branch
super-AGB Blue loop Protoplanetary nebula Planetary nebula PG1159 Dredge-up OH/IR Instability strip Luminous blue variable Blue straggler Stellar population Supernova Superluminous supernova / Hypernova

Spectral classification

Early Late Main sequence
O B A F G K M Brown dwarf WR OB Subdwarf
O B Subgiant Giant
Blue Red Yellow Bright giant Supergiant
Blue Red Yellow Hypergiant
Yellow Carbon
S CN CH White dwarf Chemically peculiar
Am Ap/Bp HgMn Helium-weak Barium Extreme helium Lambda Boötis Lead Technetium Be
Shell B[e]


White dwarf
Helium planet Black dwarf Neutron
Radio-quiet Pulsar
Binary X-ray Magnetar Stellar black hole X-ray binary


Blue dwarf Green Black dwarf Exotic
Boson Electroweak Strange Preon Planck Dark Dark-energy Quark Q Black Gravastar Frozen Quasi-star Thorne–Żytkow object Iron Blitzar

Stellar nucleosynthesis

Deuterium burning Lithium burning Proton–proton chain CNO cycle Helium flash Triple-alpha process Alpha process Carbon burning Neon burning Oxygen burning Silicon burning S-process R-process Fusor Nova
Symbiotic Remnant Luminous red nova


Core Convection zone
Microturbulence Oscillations Radiation zone Atmosphere
Photosphere Starspot Chromosphere Stellar corona Stellar wind
Bubble Bipolar outflow Accretion disk Asteroseismology
Helioseismology Eddington luminosity Kelvin–Helmholtz mechanism


Designation Dynamics Effective temperature Luminosity Kinematics Magnetic field Absolute magnitude Mass Metallicity Rotation Starlight Variable Photometric system Color index Hertzsprung–Russell diagram Color–color diagram

Star systems

Contact Common envelope Eclipsing Symbiotic Multiple Cluster
Open Globular Super Planetary system


Solar System Sunlight Pole star Circumpolar Constellation Asterism Magnitude
Apparent Extinction Photographic Radial velocity Proper motion Parallax Photometric-standard


Proper names
Arabic Chinese Extremes Most massive Highest temperature Lowest temperature Largest volume Smallest volume Brightest
Historical Most luminous Nearest
Nearest bright With exoplanets Brown dwarfs White dwarfs Milky Way novae Supernovae
Candidates Remnants Planetary nebulae Timeline of stellar astronomy

Related articles

Substellar object
Brown dwarf Sub-brown dwarf Planet Galactic year Galaxy Guest Gravity Intergalactic Planet-hosting stars Tidal disruption event

Physics Encyclopedia



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