Light and dark

PREFACE ix 1 ESSENTIAL, USEFUL AND FRIVOLOUS LIGHT 1 1.1 Light for life 1 1.2 Wonder and worship 4 1.3 Artificial illumination 6 1.3.1 Light from combustion 6 1.3.2 Arc lamps and filament lamps 9 1.3.3 Gas discharge lamps 13 1.4 Light in art and entertainment 15 2 PATTERNS OF SUNLIGHT 19 2.1 The year 19 2.2 Equinoxes and eccentricity 22 2.3 The length of a day 26 2.4 The length of daylight 31 2.5 The length of a second 37 3 MONTHS AND MOONLIGHT 41 3.1 The lunar month and the lunar orbit 41 3.2 The lunar nodes and their rotation 43 3.3 The lunar day 48 3.4 The length of moonlight 50 3.5 Eclipses and Saros cycles 55 3.5.1 Eclipses and history 55 3.5.2 The Saros cycle 55 3.5.3 Total and annular solar eclipses 61 3.6 Tides 63 4 HISTORY, DATES AND TIMES 67 4.1 Solar calendars 67 4.2 The Roman Catholic Church and the development of astronomy 704.3 The start of the year 72 4.4 Lunar and other calendars 73 4.5 Time zones 77 4.6 The International Date Line 80 5 LIGHT AND THE ATMOSPHERE 84 5.1 Scattered light and twilight 84 5.2 Polarization of light 88 5.3 Rainbows 94 5.4 Cloudy skies 98 5.5 Halos 99 6 SEEING THE LIGHT 103 6.1 The human eye 103 6.2 Colour vision and colour blindness 109 6.2.1 Colour vision 109 6.2.2 Colour blindness 112 6.3 Polarization sensitivity 114 6.4 Speed of response 115 6.5 Optical illusions 118 7 ZOOLOGICAL DIVERSIONS 129 7.1 Colour vision in animals 129 7.2 Zebras 131 7.2.1 Species and subspecies 131 7.2.2 Other zebra-striped animals 133 7.3 Piebald coats and unusual goats 134 7.4 Jellicle cats are black and white 138 7.5 Cephalopods 142 7.6 Lighting up for a mate or a meal 144 7.6.1 Bioluminescence in insects 144 7.6.2 Bioluminescence in deep-sea fish 146 7.7 More anatomical oddities 147 8 INFORMATION IN LIGHT 150 8.1 Lighthouses 150 8.2 Semaphores for optical telegraphy 154 8.3 Morse, Mance and the heliograph 163 8.4 Bell and the photophone 1669 LIGHT IN THE ERA OF ELECTRONICS 170 9.1 Electronics 1900–1960 170 9.1.1 Early rectification devices 170 9.1.2 The solid-state rectifier 172 9.1.3 The transistor 175 9.2 New semiconductors for optoelectronics 177 9.3 Optoelectronic semiconductor devices 182 9.4 Bright light from cool solids 187 10 OPTICAL COMMUNICATION TODAY 193 10.1 Waveguides and optical fibres 193 10.2 The transparency of glass 195 10.3 Optical fibres 198 10.4 Optical amplification 203 10.5 Conveying sound by light 204 10.6 The long and the short of optical communication 210