Sunspots are temporary phenomena on the photosphere of the Sun that appear visibly as dark spots compared to surrounding regions. They are caused by intense magnetic activity, which inhibits convection by an effect comparable to the eddy current brake, forming areas of reduced surface temperature. Like magnets, they also have two poles. Although they are at temperatures of roughly 3000–4500 K (2727–4227 °C), the contrast with the surrounding material at about 5780 K (5500 °C) leaves them clearly visible as dark spots, as the luminous intensity of a heated black body (closely approximated by the photosphere) is a function of temperature to the fourth power. If the sunspot were isolated from the surrounding photosphere it would be brighter than an electric arc. Sunspots expand and contract as they move across the surface of the Sun and can be as large as 80,000 kilometers (50,000 mi) in diameter, making the larger ones visible from Earth without the aid of a telescope. They may also travel at relative speeds ("proper motions") of a few hundred m/s when they first emerge onto the solar photosphere.
Manifesting intense magnetic activity, sunspots host secondary phenomena such as coronal loops (prominences) and reconnection events. Most solar flares and coronal mass ejections originate in magnetically active regions around visible sunspot groupings. Similar phenomena indirectly observed on stars are commonly called starspots and both light and dark spots have been measured.
Other articles related to "sunspot, dark":
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... the amount of ionization possible is related to the 11-year sunspot cycle ... In times of high sunspot activity, the band can remain open to much of the world for long periods of time ... During low sunspot activity it may be impossible to use skywave at all, except during periods of sporadic electron propagation (from late spring through mid-summer) ...
1802 — William Hyde Wollaston observes dark lines in the solar spectrum 1814 — Joseph Fraunhofer systematically studies the dark lines in the ...
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Famous quotes containing the words spots and/or dark:
“The instincts of merry England lingered on here with exceptional vitality, and the symbolic customs which tradition has attached to each season of the year were yet a reality on Egdon. Indeed, the impulses of all such outlandish hamlets are pagan still: in these spots homage to nature, self-adoration, frantic gaieties, fragments of Teutonic rites to divinities whose names are forgotten, seem in some way or other to have survived mediaeval doctrine.”
—Thomas Hardy (18401928)
“Love is like the wild rose-briar;
Friendship like the holly-tree.
The holly is dark when the rose-briar blooms,
But which will bloom most constantly?”
—Emily Brontë (18181848)