ESA / NASA / SOHO / SCIENCE PHOTO LIBRARY ESA / NASA / SOHO / SCIENCE PHOTO LIBRARY
Taken from space by the Solar and Heliospheric Observatory (SOHO), this composite image of our Sun shows a dramatically different picture than the one we receive on Earth. Launched in 1995, SOHO has been continuously monitoring the Sun. In 2006, one image for each year of the mission until then was chosen and displayed in this montage. The bright parts of these images correspond to gas in the Sun's atmosphere at a temperature of about 2 million degrees Celsius. Unlike visible light, the intensity of the ultraviolet radiation from the Sun varies greatly. This variation becomes more pronounced the shorter the wavelength, especially in the X-ray region of the spectrum. This is governed by solar activity, which runs in an approximately 11-year cycle. It is linked to the generation of the Sun's magnetic field, though our precise understanding of this mechanism remains elusive. The cycles have been counted since 1755 when systematic record-taking began.
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