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The photosphere is a star's outer shell from which light is radiated.

The term itself is derived from Ancient Greek roots, φῶς, φωτός/phos, photos meaning "light" and σφαῖρα/sphaira meaning "sphere", in reference to it being a spherical surface that is perceived to emit light. It extends into a star's surface until the plasma becomes opaque, equivalent to an optical depth of approximately ​2⁄3,[1] or equivalently, a depth from which 50% of light will escape without being scattered.

A photosphere is the deepest region of a luminous object, usually a star, that is transparent to photons of certain wavelengths.

Temperature

The surface of a star is defined to have a temperature given by the effective temperature in the Stefan–Boltzmann law. Stars, except neutron stars, have no solid or liquid surface.[2] Therefore, the photosphere is typically used to describe the Sun's or another star's visual surface.
Composition of the Sun

The Sun is composed primarily of the chemical elements hydrogen and helium; they account for 74.9% and 23.8% of the mass of the Sun in the photosphere, respectively. All heavier elements, called metals in astronomy, account for less than 2% of the mass, with oxygen (roughly 1% of the Sun's mass), carbon (0.3%), neon (0.2%), and iron (0.2%) being the most abundant.
Sun
Solar atmosphere: temperature and density.[3] See here for meanings of extra lines in the graph.

The Sun's photosphere has a temperature between 4,500 and 6,000 K (4,230 and 5,730 °C)[4] (with an effective temperature of 5,777 K (5,504 °C))[5] and a density of about 3×10−4 kg/m3;[6] increasing with depth into the sun.[3] Other stars may have hotter or cooler photospheres. The Sun's photosphere is around 100 kilometers thick, and is composed of convection cells called granules—cells of plasma each approximately 1000 kilometers in diameter with hot rising plasma in the center and cooler plasma falling in the narrow spaces between them, flowing at velocities of 7 kilometer per second. Each granule has a lifespan of only about twenty minutes, resulting in a continually shifting "boiling" pattern. Grouping the typical granules are super granules up to 30,000 kilometers in diameter with lifespans of up to 24 hours and flow speeds of about 500 meter per second, carrying magnetic field bundles to the edges of the cells. Other magnetically-related phenomena include sunspots and solar faculae dispersed between the granules.[7] These details are too fine to be seen when observing other stars from earth.
Other layers of the Sun

The Sun's visible atmosphere has other layers above the photosphere: the 2,000 kilometer-deep chromosphere (typically observed by filtered light, for example H-alpha) lies just between the photosphere and the much hotter but more tenuous corona. Other "surface features" on the photosphere are solar flares and sunspots.
References

Carroll, Bradley W. & Ostlie, Dale A. (1996). Modern Astrophysics. Addison-Wesley.
As of 2004, although white dwarfs are believed to crystallize from the middle out, none have fully solidified yet [1]; and only neutron stars are believed to have a solid, albeit unstable [2], crust [3]
John A. Eddy (1979). "SP-402 A New Sun: The Solar Results From Skylab". NASA.
The Sun – Introduction
World Book at NASA – Sun
Stanford Solar Center (2008). "The Sun's Vital Statistics".

"NASA/Marshall Solar Physics". NASA.

External links

Animated explanation of the Photosphere (University of South Wales).
Animated explanation of the temperature of the Photosphere (University of South Wales).
Solar Lower Atmosphere and Magnetism (MPS)

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The Sun
Internal structure

Core Radiation zone Tachocline Convection zone


The Sun by the Atmospheric Imaging Assembly of NASA's Solar Dynamics Observatory - 20100819.jpg
Atmosphere
Photosphere

Supergranulation Granule Faculae Sunspot

Chromosphere

Plage Spicule Moreton wave

Corona

Transition region Coronal hole Coronal loop Coronal mass ejection Prominence Helmet streamer Supra-arcade downflows

Variation

Solar cycle
List of solar cycles Solar maximum Solar minimum Wolf number Solar wind Flare Helioseismology

Heliosphere

Current sheet Termination shock Heliosheath Heliopause Bow shock

Related

Eclipse Heliophysics In culture
solar deities Solar activity Solar astronomy Solar dynamo Solar energy Solar neutrino Solar observation Solar phenomena Solar physics Solar System Solar telescope Solar time Space climate Space weather Standard solar model Star Sunlight radiation

Spectral class: G-type main-sequence star

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Stars
Formation

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

Evolution

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]

Remnants

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

Hypothetical

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

Structure

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

Properties

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

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

Earth-centric
observations

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

Lists

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

World

Index

Hellenica World - Scientific Library

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