English: This picture of the largest sunspot group in a decade shows the Sun as seen by a film camera at the National Science Foundation's McMath-Pierce Telescope at Kitt Peak, AZ, on Friday morning, March 30, 2001. It was taken by Dr. Bill Livingston, a staff member of the National Solar Observatory in Tucson, AZ.This whole sunspot covers more than 140,000 kilometers (86,8000 miles), 22 times the diameter of Earth, over the Sun's northern hemisphere. The darkest of the structures are the sunspot umbrae, where the magnetic fields are locally vertical. They are surrounded by lighter fibrous channels called sunspot penumbrae, where the magnetic fields are locally horizontal. The surrounding bubbly structures are known as photospheric granules, which are about 1000-2000 km (620-1,240 miles) across.This large sunspot group is visible on the sun with the naked eye, when sufficient filters are used to prevent damage to the eyes.The National Solar Observatory is operated by the Association of Universities Research in Astronomy, Inc.(AURA), for the National Science Foundation.