The Sun and The Origins Of The Solar System sunspots and established the period as 11 years Wolf also introduced what is termed the Zurich relative relative sunspot number a value equal to the sum of the spots plus 10 times the number of groups which is still used today Illustration from Galileo’s History and Demonstrations Concerning Sunspots and Their Properties or Letters on Sunspots Sunspots 1613 Much of the work at this time was carried out by wealthy amateurs such as Richard Christopher Carrington of Britain who built a private observatory and discovered the differential differential rotation and the equatorward drift of activity during a sunspot cycle He was the first with another Englishman R Hodgson to observe a solar flare Photographic monitoring monitoring began in 1860 and soon spectroscopy was applied to the Sun so elements present in the Sun and their physical physical state could begin to be investigated In the early part of the 19th century Joseph von Fraunhofer mapped the solar spectrum At the end of the 19th century spectroscopy during eclipses revealed the character of the atmosphere but the million-degree coronal temperature was not established 12
Understanding The Sun established until observations of coronal spectral lines were made in 1940 by the German German astrophysicist Walter Grotrian Drawings of sunspots from German mathematician Christoph Scheiner’s Rosa Ursina 1630 In 1891 while he was a senior at the Massachusetts Institute of Technology in Cambridge Massachusetts Massachusetts George Ellery Hale invented the spectroheliograh spectroheliograh which can be used to take pictures of the Sun in any single wavelength After using the instrument on the great Yerkes refractor refractor in Williams Bay Wisconsin U.S Hale developed the Mount Wilson Observatory in California and built the first solar tower telescopes there Prior to the construction of the Mount Wilson facility all solar observatories were located in cloudy places and long-term studies were not possible Hale discovered the magnetic fields of sunspots by observing the splitting of their spectral lines into a number of components this splitting known as the Zeeman Zeeman effect occurs in the presence of a strong magnetic field By continuously studying the spots for two cycles 13
The Sun and The Origins Of The Solar System he discovered with the American astronomer Seth Barnes Nicholson Nicholson the law of sunspot polarities Later in Photograph of a solar eclipse at Rivabellosa Spain July 18 1860 team 1953 the American father and-son of astronomers Harold and Horace Babcock working with the same instruments developed the magnetograph with which the polar field was detected In the 1930s the French astronomer Bernard Lyot introduced the coronagraph which made possible spectral observations of the corona when the Sun is not in eclipse and the birefringent filter filter which permitted two-dimensional monochromatic images With the Lyot filter cinematography of the solar activity of magnetic and velocity fields became a reality In the 1960s the American astronomer Robert Leighton modified Hale’s spectroheliograph so that it could measure measure both velocities and magnetic fields and with it discovered discovered solar oscillations 14
underSTanding The Sun After 1950 new observatories were established in areas that were less cloudy By 1960 astronomers realized that these sites not only had to be clear but that they also had to have stable air By locating observatories near lakes and by employing electronic imaging and vacuum telescopes telescopes astronomers were able to make new higher-resolution higher-resolution observations In 1969 the movement began with the Aerospace Corporation Observatory now the San Fernando Observatory and the Big Bear Solar Observatory Observatory both in California Free of ground effects these observatories achieved a new level of stable images and were soon followed by lake-sited solar observatories in India and China An entirely new dimension of solar studies was initiated initiated by the space age With one or two exceptions all of the important spectral lines from the chromosphere and corona are in the ultraviolet and since the photosphere is relatively weak in the ultraviolet it is easy to disentangle the images of the upper layer from the powerful visible radiation of the photosphere Moreover satellites sampling sampling the solar particles have the ability to monitor directly solar waves and particles that do not reach the ground However the task is not easy Ultraviolet optics demanded special coatings and films now charge-coupled devices for observing Special solar trackers were required to keep the image steady and good telemetry was needed for the 15
