Sun spots

(Astron.)

dark spots that appear on the sun's disk, consisting commonly of a black central portion with a surrounding border of lighter shade, and usually seen only by the telescope, but sometimes by the naked eye. They are very changeable in their figure and dimensions, and vary in size from mere apparent points to spaces of 50,000 miles in diameter. The term sun spots is often used to include bright spaces (called faculæ) as well as dark spaces (called maculæ). Called also solar spots. See Illustration in Appendix.