[...]... lead The core extends one-quarter of the way from the centre of the globe to the outer surface; about THE DATA BOOK OF ASTRONOMY 13 THE SUN 37% of the original hydrogen has been converted to helium Outside the core comes the radiative zone, extending out to 70% between the centre and the surface; here, energy is transported by radiative diffusion In the outer layers it is convection which is the transporting... DATA BOOK OF ASTRONOMY 17 THE SUN Table 2.11 Structure of the Sun Core Radiative zone The region where energy is being generated The outer edge lies about 175 000 km from the Sun’s centre The core temperature about 15 000 000 ◦ C; the density 150 g cm−3 (10 times the density of lead) The temperature at the outer edge is about half the central value Extends from the outer edge of the core to the interface... will merge with the interstellar medium and cease to be identifiable This ‘heliopause’ marks the outer edge of the heliosphere, the area of space inside which the Sun’s influence is dominant ECLIPSES OF THE SUN A solar eclipse occurs when the Moon passes in front of the Sun; strictly speaking, the phenomenon is an occultation of the Sun by the Moon Eclipses may be total (when the whole of the photosphere... Chronicle; the eclipse took place on 15 February 538, four years after the death of Cerdic, the first King of the West Saxons The Sun was two-thirds eclipsed from London The celebrated chronicler William of Malmesbury gave a graphic description of the eclipse of 1133: the Sun ‘shrouded his glorious face, as the poets say, in hideous darkness, agitating the hearts of men by an eclipse and on the sixth day of the. .. dome-shaped Dunes Valley Widespread lowland plain THE DATA BOOK OF ASTRONOMY 3 2 THE SUN The Sun, the controlling body of the Solar System, is the only star close enough to be studied in detail It is 270 000 times closer than the nearest stars beyond the Solar System, those of the Alpha Centauri group Data are given in Table 2.1 Table 2.1 The Sun: data Distance from Earth: mean 149 597 893 km (1 astronomical... 34.0 THE SOLAR CONSTANT This may be defined as being the amount of energy in the form of solar radiation which is normally received on unit area at the top of the Earth’s atmosphere; it is roughly equal to the amount of energy reaching ground level on a clear day The first measurements were made by Sir John Herschel THE DATA BOOK OF ASTRONOMY 5 THE SUN in 1837–8, using an actinometer (basically a bowl of. .. that of 16 December 2085 for only 19 s The largest partial eclipse of the 21st century will be that of 11 April 2051, when the Sun will be 98.5% THE DATA BOOK OF ASTRONOMY 23 THE SUN obscured On 24 October 2098 the obscuration amounts to no more than 0.004% The longest totality ever observed was during the eclipse of 30 June 1973 A Concorde aircraft, specially equipped for the purpose, flew underneath the. .. made by the Greeks There does seem good evidence that the eclipse of 25 May 585 BC was predicted by Thales of Miletus, the first of the great Greek philosophers It occurred near sunset in the Mediterranean area, and is said to have put an end to a battle between the forces of King Alyattes of the Lydians and King Cyraxes of the Medes; the combatants were so alarmed by the sudden darkness that they concluded... a theory according to which the planets were pulled off the Sun by the action of a passing star; a cigar-shaped tongue of material would be pulled out and this would break up into planets, with the largest planets (Jupiter and Saturn) in the middle part of the system, where the thickest part of the ‘cigar’ would have been Again there were insuperable mathematical objections, and a modification of the. .. from Cambridge University His 1970 book, The Temperate Sun, is indeed a remarkable work THE DATA BOOK OF ASTRONOMY 11 THE SUN Table 2.8 The chemical elements and their occurrence in the Sun The following is a list of elements 1 to 92 ∗ = detected in the Sun R = included in H A Rowland’s list published in 1891 For elements 43, 61, 85–89 and 91 the mass number is that of the most stable isotope Atomic number . value as derived from the close approach of the asteroid Eros in 1931 was too high. 4 THE DATA BOOK OF ASTRONOMY THE SUN Table 2.2. Selected estimates of the length of the astronomical unit. Parallax Year. angle. The cause of these anomalies is unclear. ORIGIN OF THE SOLAR SYSTEM In investigating the origin of the planetary system we do have one important piece of information: the age of the Earth. lowland plain THE DATA BOOK OF ASTRONOMY 3 2THE SUN The Sun, the controlling body of the Solar System, is the only star close enough to be studied in detail. It is 270 000 times closer than the nearest