As you know, the angle of the sun's rays on our planet is responsible for bringing about our various seasons. What you might not be aware of, however, is that the sun itself goes through its own seasons.
A new image just released by the European Space Agency (ESA) shows these changes by stringing together one shot of the sun every year for 20 years. The images were all taken by the extreme ultraviolet imaging telescope aboard the Solar and Heliospheric Observatory (SOHO), an ESA-NASA spacecraft that has been looking at the sun steadily for two decades. SOHO is fixed in orbit at a point between the Earth and the sun in such a way that it's always got an eye on the great ball of fire at the center of our solar system; it never gets eclipsed by the Earth.
The images that are the brightest in this composite show the times when the sun was most active, during solar maximums. These are the times when the sun's magnetic field is extremely active and sunspots are at their most plentiful. The darker images represent solar minimums, when the sun settles down for a bit.
"Years ago, in 2008 and 2009, an eerie quiet descended on the sun," says a NASA article on solar minimums and maximums. "Sunspot counts dropped to historically low levels and solar flares ceased altogether. As the longest and deepest solar minimum in a century unfolded, bored solar physicists wondered when 'Solar Max' would ever return."
NASA researchers say that the wondering is over and we're in a solar maximum right now, though it's a relatively weak one. It's generally believed that solar cycles take 11 years, but the space agency says 9 to 14 years is a more accurate gauge of the sun's seasons, during which it goes from a spectacular sizzle to a more tame simmer.