Sunspots

25 April, 2010

Sunspots made more visible by fires in Southern California.
Sunspots made more visible by fires in Southern California.
Image: NASA
Source: NASA

The Sun is a massive ball of very hot gasses held together by gravity. It is composed mostly of hydrogen (70% by mass) and helium (28%), as well as small amounts of other elements such as oxygen, nitrogen and carbon. It has no solid surface but its atmosphere has several layers.

The layer of the sun that we can observe, sometimes referred to as its surface, is called the photosphere. The photosphere has a granulated appearance arising from convection currents, like boiling water in a saucepan. Dark patches can sometimes appear on the photosphere and these are called sunspots.

Sunspots are caused by the appearance of cooler (4000° C) areas amidst the roiling gases on the surface (6000° C). Sunspots are magnetic, with magnetic field strengths thousands of times stronger than the Earth's magnetic field. They typically last for several days, although very large ones may live for several weeks.

Sunspots usually come in groups that consists of two sets of spots. They are closely watched by space weather forecasters because they can be a sign of a potential space weather storm. Like high and low pressure systems on Earth, these hot and cool patches on the Sun can be an indication of the severity of future ionospheric activity, otherwise known as space weather.

Ordinary thunderstorms, however, are not triggered by space weather. They are caused by upward movement of warm moist air caused by thermal activity in the lower atmosphere. There is a weak connection between ordinary thunderstorms and ionospheric storms in that the upward motion of air in thunderstorms can cause a disturbance in the ionosphere and thus affect space weather, but there is no known mechanism whereby space weather has an influence on ordinary weather.

It is believed that Galileo Galilei made the first European observations of sunspots in 1610.

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Sunspot Sunspots and an indication of the size of the Sun relative to Jupiter and Earth.

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