Long-term studies of photospheric magnetic fields on the Sun

We briefly review the history of observations magnetic fields on Sun, and describe early magnetograps for full disk measurements. Changes in instruments detectors, cohort observers, knowledge base etc may result non-uniformity long-term synoptic datasets. Still, such data are critical detecting understanding trends solar activity. demonstrate value historical using studies active region tilt (Joy’s law) evolution polar field its reversal. Using longest dataset sunspot strength measurements from Mount Wilson Observatory (1917-present) supplemented by shorter datasets Pulkovo (1956–1997) Crimean (1956-present) observatories we that properties sunspots did not change over last hundred years. also show relationship between area flux can be used to extend periods with no direct Finally, how more recent vector study (solar cycle) variations helicity Sun.