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The strongest observed solar magnetic fields are found in sunspot umbrae and associated light bridges. We investigate systematic measurements of approximately 32 000 sunspot groups observed from 1917 through 2004 using data from Mt. Wilson, Potsdam, Rome and Crimea observatories. Isolated observations from other observatories are also included. Corrections to Mt. Wilson measurements are required and...
The locations of coronal holes are usually based on equivalent-width images in the He i 1083 nm line. However, it is difficult to differentiate coronal holes from the centers of quiet chromospheric network without complementary data and the skill of an experienced observer. Analysis of imaging spectroscopy shows that line half-width and central intensity are correlated differently in coronal holes...