CHAPTER 1 Understanding the sUn Although the Sun is a rather ordinary star it is the source of virtually all Earth’s energy It provides the heat and light that make life on Earth possible Yet Earth receives only about half a billionth of the energy that leaves the Sun The telescope has been used in solar studies since 1610 The solar tower telescope was later invented for use in solar studies Its long focal length can give very large images of the Sun The coronagraph another special telescope is used to examine the Sun’s outer atmosphere The instrument blocks the direct light from the Sun’s disk allowing the much dimmer corona to be viewed The Italian scientist Galileo Galilei and the German mathematician Christoph Scheiner were among the first to make telescopic observations of sunspots Scheiner’s drawings in the Rosa Ursina are of almost modern quality and there was little improvement in solar imaging until 1905 In the 1670s the British astronomer John Flamsteed 10
The sunset over Joshua Tree National Park in California and the French astronomer Gian Domenico Cassini calculated calculated the distance to the Sun Sir Isaac Newton set forth the role of the Sun as the centre of attraction of the known planetary system The sunspot cycle a huge effect was not discovered until 1843 by Samuel Heinrich Schwabe The German amateur astronomer was looking for a planet inside the orbit of Mercury and made careful daily drawings to track its passage across the face of the Sun Instead he found that the number of sunspots varied with a regular period The Swiss astronomer Rudolf Wolf confirmed Schwabe’s discovery by searching through previous reports of sunspots 11
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
