A spicule is a dynamic jet of about 500km diameter on the Sun. It moves upwards at about 20 km/s from the photosphere. They were discovered in 1877 by Father Angelo Secchi of the Vatican Observatory in Rome. The chromosphere is entirely composed of spicules. The Sun is the star at the center of the Solar System. ... The photosphere of an astronomical object is the region at which the optical depth becomes one for a photon of wavelength equal to 5000 angstroms. ... Pietro Angelo Secchi (1818–1878) was an Italian astronomer. ... The Vatican Observatory (Specola Vaticana) is the astronomical research and educational institution of the Holy See. ...
Spicules live for about 5-10 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; their mass flux is about 100 times that of the solar wind. The plasma in the solar wind meeting the heliopause For the British comic, see Solar Wind (comic). ...
Prevalence
At any one time there are around 100,000 active spicules on the Sun; 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 ), Robert Erdélyi and James P. Stewart (both from the University of Sheffield, Sheffield, UK) 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). 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. Location of Palo Alto within Santa Clara County, California. ... The University of Sheffield is a research university, located in Sheffield in South Yorkshire, England. ... A computer generated image showing the pattern of a p-mode solar acoustic oscillation both in the interior and on the surface of the sun. ...
Literature
De Pontieu, B., Erdélyi, R. and Stewart, J: Solar chromospheric spicules from the leakage of photospheric oscillations and flows In: Nature. 430/2004, p. 536–539, ISSN0028-0836
This spectrum is obtained before a solar eclipse reaches totality and is formed from the thin arc of the sun disappearing behind the moon's disk.
The elements of each layer are sometimes distributed in bright, cloudlike patches called plages, or flocculi, and in general are located along the same zones as sunspots and fluctuate with the same 11-yr cycle; the relationship between the two is not yet understood.
Most spectacular of the solar features are the streams of hot gas, called prominences, that shoot out thousands or even hundreds of thousands of miles from the sun's surface at velocities as great as 250 mi per sec (400 km per sec).
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