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    Posted January 13, 2014 by
    Darkhole
    Location
    Thrissur, India

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    Giant dark hole in the sun (06/01/2014 17:58:40 IST)

     
    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. They usually appear as pairs, with each sunspot having the opposite magnetic pole to the other.[1]

    Although they are at temperatures of roughly 3,000–4,500 K (2,700–4,200 °C), the contrast with the surrounding material at about 5,780 K (5,500 °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 the Moon.[2] Sunspots expand and contract as they move across the surface of the Sun and can be as small as 16 kilometers (10 mi)[3] and as large as 160,000 kilometers (100,000 mi)[4] in diameter, making the larger ones visible from Earth without the aid of a telescope.[5] They may also travel at relative speeds ("proper motions") of a few hundred meters per second when they first emerge
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