Astronomy Picture of the Day . An Active Sunspot Viewed Sideways . ... Credit Copyright: Hinode , JAXA , NASA Explanation: Why are there dark spots on the sun? Although noted for thousands of years, sunspots have been known for decades to be regions of the Sun that are slightly depressed and cooled by the Sun's complex and changing magnetic field . ... Publications with keywords: sunspot - magnetic field - Sun . Publications with words: sunspot - magnetic field - Sun . ...