One year of the sun's activity captured in one image
Released on Earth Day, this photo of the sun is actually many photos layered over one another. It reveals where the sun has been most active during the last year.
NASA states, "In the three years since it first provided images of the sun in the spring of 2010, NASA’s Solar Dynamics Observatory has had virtually unbroken coverage of the sun's rise toward solar maximum, the peak of solar activity in its regular 11-year cycle. This image is a composite of 25 separate images spanning the period of April 16, 2012, to April 15, 2013. It uses the SDO AIA wavelength of 171 angstroms and reveals the zones on the sun where active regions are most common during this part of the solar cycle."
You can watch this video to watch the sun's activity over a 3-year time period.