Halpha_%2B700_limb_spicules_08Aug2007_SST

solar physics Solar physics is the branch of astrophysics that specializes in the study of the Sun. It intersects with many disciplines of pure physics and astrophysics. Because the Sun is uniquely situated for close-range observing (other stars cannot be re ...

, 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 centre of the Solar System. It is a massive, nearly perfect sphere of hot plasma, heated to incandescence by nuclear fusion reactions in its core, radiating the energy from its surface mainly as visible light a ...

chromosphere A chromosphere ("sphere of color", from the Ancient Greek words χρῶμα (''khrôma'') 'color' and σφαῖρα (''sphaîra'') 'sphere') is the second layer of a Stellar atmosphere, star's atmosphere, located above the photosphere and below t ...

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. It extends into a star's surface until the plasma becomes opaque, equivalent to an optical depth of approximately , or equivalently, a depth from which 50% of light will esc ...

and last a few minutes each before falling back to the solar atmosphere. They were discovered in 1877 by

Angelo Secchi Angelo Secchi (; 28 June 1818 – 26 February 1878) was an Italians, Italian Priesthood in the Catholic Church, Catholic priest and astronomer from the Regions of Italy, Italian region of Emilia-Romagna, Emilia. He was director of the observato ...

, 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 high

magnetic 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 we ...

; their

mass flux In physics and engineering, mass flux is the rate of mass flow per unit of area. Its SI units are kgs−1m−2. The common symbols are ''j'', ''J'', ''q'', ''Q'', ''φ'', or Φ (Greek lowercase or capital Phi), sometimes with subscript ''m'' to i ...

is about 100 times that of the

solar wind The solar wind is a stream of charged particles released from the Sun's outermost atmospheric layer, the Stellar corona, corona. This Plasma (physics), plasma mostly consists of electrons, protons and alpha particles with kinetic energy betwee ...

. 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 the

. An individual spicule typically reaches 3,000–10,000 km altitude above the photosphere.

Causes

Bart De Pontieu ( Lockheed Martin Solar and Astrophysics Laboratory,

Palo Alto, California Palo Alto ( ; Spanish language, Spanish for ) is a charter city in northwestern Santa Clara County, California, United States, in the San Francisco Bay Area, named after a Sequoia sempervirens, coastal redwood tree known as El Palo Alto. Th ...

, United States), Robert Erdélyi and Stewart James (both from the

University of Sheffield The University of Sheffield (informally Sheffield University or TUOS) is a public university, public research university in Sheffield, South Yorkshire, England. Its history traces back to the foundation of Sheffield Medical School in 1828, Fir ...

, United Kingdom) hypothesised in 2004 that spicules form 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 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 surface. It is similar to geoseismol ...

). Magnetic flux tubes that are tilted away from the vertical can focus and guide the rising material up into the solar atmosphere to form a spicule. However, there is still some controversy about the issue in the solar physics community.

Notes

References

External links

* {{DEFAULTSORT:Spicule (Solar Physics) Solar phenomena