Physics Gifts

- Art Gallery -

The chromosphere (literally, "sphere of color") is the second of the three main layers in the Sun's atmosphere and is roughly 3,000 to 5,000 kilometers deep. Its rosy red color is only apparent during eclipses. The chromosphere sits just above the photosphere and below the solar transition region. The layer of the chromosphere atop the photosphere is homogeneous. A forest of hairy-appearing spicules rise from the homogeneous layer, some of which extend 10,000 km into the corona above.

The density of the chromosphere is only 10−4 times that of the photosphere, the layer beneath, and 10−8 times that of the atmosphere of Earth at sea level. This makes the chromosphere normally invisible and it can be seen only during a total eclipse, where its reddish color is revealed. The color hues are anywhere between pink and red.[1] Without special equipment, the chromosphere cannot normally be seen due to the overwhelming brightness of the photosphere beneath.

The density of the chromosphere decreases with distance from the center of the Sun. This decreases exponentially from 1017 particles per cubic centimeter, or approximately 2×10−4 kg/m3 to under 1.6×10−11 kg/m3 at the outer boundary.[2] The temperature decreases from the inner boundary at about 6,000 K[3] to a minimum of approximately 3,800 K,[4] before increasing to upwards of 35,000 K[3] at the outer boundary with the transition layer of the corona.

Chromospheres have been observed also in stars other than the Sun.[5] The Sun's chromosphere has been hard to examine and decipher, although observations continue with the help of the electromagnetic spectrum.[6]

Comparing chromosphere and photosphere

Whilst the photosphere has an absorption line spectrum, the chromosphere's spectrum is dominated by emission lines. In particular, one of its strongest lines is the Hα at a wavelength of 656.3 nm; this line is emitted by a hydrogen atom whenever its electron makes a transition from the n=3 to the n=2 energy level. A wavelength of 656.3 nm is in the red part of the spectrum, which causes the chromosphere to have its characteristic reddish colour.

By analysing the spectrum of the chromosphere, it was found that the temperature of this layer of the solar atmosphere increases with increasing height in the chromosphere itself. The temperature at the top of photosphere is only about 4,400 K, while at the top of chromosphere, some 2,000 km higher, it reaches 25,000 K.[1][7] This is however the opposite of what we find in the photosphere, where the temperature drops with increasing height. It is not yet fully understood what phenomenon causes the temperature of the chromosphere to paradoxically increase further from the Sun's interior. However, it seems likely to be explained, partially or totally, by magnetic reconnection.
Features

Many interesting phenomena can be observed in the chromosphere, which is very complex and dynamic:

Filaments (and prominences, which are filaments viewed from the side) underlie many coronal mass ejections and hence are important to the prediction of space weather. Solar prominences rise up through the chromosphere from the photosphere, sometimes reaching altitudes of 150,000 km. These gigantic plumes of gas are the most spectacular of solar phenomena, aside from the less frequent solar flares.
The most common feature is the presence of spicules, long thin fingers of luminous gas which appear like the blades of a huge field of fiery grass growing upwards from the photosphere below. Spicules rise to the top of the chromosphere and then sink back down again over the course of about 10 minutes. Similarly, there are horizontal wisps of gas called fibrils, which last about twice as long as spicules.
Images taken in typical chromospheric lines show the presence of brighter cells, usually called as network, while the surrounding darker regions are named internetwork. They look similar to granules commonly observed on the photosphere due to the heat convection.
Periodic oscillations have been found since the first observations with the instrument SUMER on board SOHO with a frequency from 3 mHz to 10 mHz, corresponding to a characteristic periodic time of three minutes.[8] Oscillations of the radial component of the plasma velocity are typical of the high chromosphere. Now we know that the photospheric granulation pattern has usually no oscillations above 20 mHz while higher frequency waves (100 mHz or a 10 s period) were detected in the solar atmosphere (at temperatures typical of the transition region and corona) by TRACE.[9]
Cool loops can be seen at the border of the solar disk. They are different from prominences because they look as concentric arches with maximum temperature of the order 0.1 MK (too low to be considered coronal features). These cool loops show an intense variability: they appear and disappear in some UV lines in a time less than an hour, or they rapidly expand in 10–20 minutes. Foukal [10] studied these cool loops in detail from the observations taken with the EUV spectrometer on Skylab in 1976. Otherwise, when the plasma temperature of these loops becomes coronal (above 1 MK), these features appear more stable and evolve on longer times.

See the flash spectrum of the solar chromosphere (Eclipse of March 7, 1970).
On other stars

A spectroscopic measure of chromospheric activity on other stars is the Mount Wilson S-index.[11][12] See also Superflare#Spectroscopic observations of superflare stars.
See also

Plage (astronomy)
Orders of magnitude (density)
Moreton wave

References

Freedman, R. A.; Kaufmann III, W. J. (2008). Universe. New York, USA: W. H. Freeman and Co. p. 762. ISBN 978-0-7167-8584-2.
Kontar, E. P.; Hannah, I. G.; Mackinnon, A. L. (2008), "Chromospheric magnetic field and density structure measurements using hard X-rays in a flaring coronal loop", Astronomy and Astrophysics, 489 (3): L57, arXiv:0808.3334, Bibcode:2008A&A...489L..57K, doi:10.1051/0004-6361:200810719
"SP-402 A New Sun: The Solar Results From Skylab". Archived from the original on 2004-11-18.
Avrett, E. H. (2003), "The Solar Temperature Minimum and Chromosphere", ASP Conference Series, 286: 419, Bibcode:2003ASPC..286..419A, ISBN 978-1-58381-129-0
"The Chromosphere". Archived from the original on 2014-04-04. Retrieved 2014-04-28.
Jess, D.B; Morton, RJ; Verth, G; Fedun, V; Grant, S.T.D; Gigiozis, I. (July 2015). "Multiwavelength Studies of MHD Waves in the Solar Chromosphere". Space Science Reviews. 190 (1–4): 103–161. arXiv:1503.01769. Bibcode:2015SSRv..190..103J. doi:10.1007/s11214-015-0141-3.
"World Book at NASA – Sun".[dead link]
Carlsson, M.; Judge, P.; Wilhelm, K. (1997). "SUMER Observations Confirm the Dynamic Nature of the Quiet Solar Outer Atmosphere: The Internetwork Chromosphere". The Astrophysical Journal. 486 (1): L63. arXiv:astro-ph/9706226. Bibcode:1997ApJ...486L..63C. doi:10.1086/310836.
De Forest, C.E. (2004). "High-Frequency Waves Detected in the Solar Atmosphere". The Astrophysical Journal. 617 (1): L89. Bibcode:2004ApJ...617L..89D. doi:10.1086/427181.
Foukal, P.V. (1976). "The pressure and energy balance of the cool corona over sunspots". The Astrophysical Journal. 210: 575. Bibcode:1976ApJ...210..575F. doi:10.1086/154862.
Observational evidence for enhanced magnetic activity of superflare stars

A small survey of the magnetic fields of planet-hosting stars gives "Wright J. T., Marcy G. W., Butler R. P., Vogt S. S., 2004, ApJS, 152, 261" as a ref for s-index.

External links

Animated explanation of the Chromosphere (and Transition Region) (University of South Wales).
Animated explanation of the temperature of the Chromosphere (and Transition Region)[permanent dead link] (University of South Wales).

vte

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

vte

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

Retrieved from "http://en.wikipedia.org/"
All text is available under the terms of the GNU Free Documentation License