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In solar physics
Solar physics is the branch of astrophysics that specializes in the study of the Sun. It deals with detailed measurements that are possible only for our closest star. It intersects with many disciplines of pure physics, astrophysics, and compu ...
, a spicule, also known as a fibril or mottle, is a dynamic jet of plasma in the Sun
The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...
's chromosphere
A chromosphere ("sphere of color") is the second layer of a star's atmosphere, located above the photosphere and below the solar transition region and corona. The term usually refers to the Sun's chromosphere, but not exclusively.
In the Su ...
about 300 km in diameter.Quantifying Spicules, Tiago M. D. Pereira, Bart De Pontieu, and Mats Carlsson, ''The Astrophysical Journal'' 759, #1 (October 2012), pp. 18-34, , . They move upwards with speeds between 15 and 110 km/s from the photosphere
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 ...
and last a few minutes each. They were discovered in 1877 by Angelo Secchi
Angelo Secchi (; 28 June 1818 – 26 February 1878) was an Italian Catholic priest, astronomer from the Italian region of Emilia. He was director of the observatory at the Pontifical Gregorian University (then called the Roman College) for 28 y ...
, but the physical mechanism that generates them is still hotly debated.
Description
Spicules last for about 15 minutes; at the solar limb they appear elongated (if seen on the disk, they are known as "mottles" or "fibrils"). They are usually associated with regions of highmagnetic flux
In physics, specifically electromagnetism, the magnetic flux through a surface is the surface integral of the normal component of the magnetic field B over that surface. It is usually denoted or . The SI unit of magnetic flux is the weber ( ...
; their mass flux
In physics and engineering, mass flux is the rate of mass flow. Its SI units are kg m−2 s−1. The common symbols are ''j'', ''J'', ''q'', ''Q'', ''φ'', or Φ (Greek lower or capital Phi), sometimes with subscript ''m'' to indicate mass is th ...
is about 100 times that of the solar wind
The solar wind is a stream of charged particles released from the upper atmosphere of the Sun, called the corona. This plasma mostly consists of electrons, protons and alpha particles with kinetic energy between . The composition of the sola ...
. They rise at a rate of 20 km/s (or 72,000 km/h) and can reach several thousand kilometers in height before collapsing and fading away.
Prevalence
There are about 3,000,000 active spicules at any one time on theSun
The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...
's chromosphere
A chromosphere ("sphere of color") is the second layer of a star's atmosphere, located above the photosphere and below the solar transition region and corona. The term usually refers to the Sun's chromosphere, but not exclusively.
In the Su ...
. An individual spicule typically reaches 3,000–10,000 km altitude above the photosphere.§1, Two Dynamical Models for Solar Spicules, Paul Lorrain and Serge Koutchmy, ''Solar Physics'' 165, #1 (April 1996), pp. 115–137, , .
Causes
Bart De Pontieu (Lockheed Martin Solar and Astrophysics Laboratory
The Lockheed Martin Solar and Astrophysics Laboratory (LMSAL) is part of the Lockheed Martin Advanced Technology Center (ATC) that is known primarily for its scientific work in the field of solar physics, astronomy and space weather. The LMSAL te ...
, Palo Alto, California
Palo Alto (; Spanish language, Spanish for "tall stick") is a charter city in the northwestern corner of Santa Clara County, California, United States, in the San Francisco Bay Area, named after a Sequoia sempervirens, coastal redwood tree kno ...
, United States), Robert Erdélyi and Stewart James (both from the University of Sheffield
, mottoeng = To discover the causes of things
, established = – University of SheffieldPredecessor institutions:
– Sheffield Medical School – Firth College – Sheffield Technical School – University College of Sheffield
, type = Pu ...
, United Kingdom) hypothesised in 2004 that spicules formed as a result of P-mode oscillations in the Sun's surface, sound waves with a period of about five minutes that causes the Sun's surface to rise and fall at several hundred meters per second (see helioseismology
Helioseismology, a term coined by Douglas Gough, is the study of the structure and dynamics of the Sun through its oscillations. These are principally caused by sound waves that are continuously driven and damped by convection near the Sun's surfa ...
). Magnetic flux tubes that tilted away from the vertical can focus and guide the rising material up into the solar atmosphere to form a spicule. There is still however some controversy about the issue in the solar physics community.
Notes
References
Literature
* De Pontieu, B., Erdélyi, R. and James, S: ''Solar chromospheric spicules from the leakage of photospheric oscillations and flows'' In: ''Nature.'' 430/2004, p. 536–539,External links
* {{DEFAULTSORT:Spicule (Solar Physics) Solar phenomena