Index

absolute time 151absorption frequency 44–5accuracy 27accurate time

availability 142uses 141–60

ACES (Atomic Clock Ensemble inSpace) 169–70

Adams, John Couch 13Airy Transit Circle 98Aldrin, Edwin 100alkali metals 39, 40ammonia clock 41–5ammonia gas 41ammonia molecule 41, 42Andromeda Galaxy 11Apollo 11 99–100Armstrong, Neil 99Association Internationale de

l’Heure 8atomic clock 1, 33–51, 65–6, 127,

141–3, 145, 150, 169,170

uses 149–54atomic second 65–6atomic time 53–67atomic timekeeping 1, 108Atomichron 62

balance wheel 26base units 156Basov, Nikolai 2

BBC radio 138BIH 71Boucheron, Pierre 30Brand, Harald 74Brouwer, Dirk 19BT 128Bullard, Sir Edward 53Bulletin A, B (IERS) 111Bunsen, Robert 33, 35, 84Bureau International de l’Heure

(BIH) 8, 63, 71, 123Bureau International des Poids et

Mesures (BIPM) 20,21, 71, 86, 89, 90, 92,96, 116, 134, 136, 158,170, 178–9

caesium 35, 39–41, 57, 66, 77,156, 164–8, 170

caesium beam clocks 69, 143caesium beam standards 45–51,

53, 62, 63, 66, 72,74–5, 82, 138–9, 149

caesium fountain 78–80, 163–70principle of 79

caesium transition 112Capella 97Central European Time 8Chandler, Seth 16chlorine 40Chu, Steven 2, 166

193

194 INDEX

Circular T (BIPM) 90, 92, 111,131

Clemence, Gerald 18, 19Clock of the Long Now 161clocks

goodness measurement 26–7hierarchy 115–16timekeeping 115traditional purpose 25

Cohen–Tannoudji, Claude 2, 166Comite International des Poids et

Mesures (CIPM) 20, 23Communications Research

Laboratory (CRL) 132computer time 129Condon, Edward 43Conference Generale des Poids et

Mesures (CGPM) 20–1,24, 54, 65, 66, 71, 156

continental drift 154Convention du Metre 20Coordinated Universal Time

(UTC) 64, 70, 71,88–92

Coordinated Universal Time Bill93–4

counter 26CS1, 2, 3, 4 caesium beam

standards 74–5

Danjon, Andre 17Danjon astrolabe 97Davis, John 145day length 3–6, 104–5, 112DCF77 127, 130, 149, 152Dehmelt, Hans 2, 174Delaunay, Charles–Eugene 13, 14digital communications networks

152–3

digital watch 26distance measurement 150Doppler, Christian 44Doppler cooling 166, 172Doppler effect 44, 45, 165Doppler Orbitography and

RadiopositioningIntegrated on Satellite(DORIS) technique102–3

Doppler shift 103, 146–7Draco 12Drullinger, Robert E. 76Dunthorne, Richard 12, 13

EAL 89, 136earthquakes 151, 155Earth’s orientation 154, 155Earth’s rotation 12, 14–16, 54, 55,

57, 58, 64, 69, 70, 72,95–7, 99, 101–8, 135

monitoring 111variation 103–8

Eddington, Sir Arthur 144EGNOS 180Einstein, Albert 133–8, 142, 145,

159electrical signals 150–1electricity transmission lines

150–1electromagnetic waves 34electron shelving 174electronic guide dog 155electronic maps 155electrons 36–9, 40energy 159ensemble clocks 80Ephemeris Time (ET) 17–19, 23,

24, 53, 54, 55, 56, 57,

INDEX 195

58, 59, 62, 70, 112equation of time 6, 16escapement mechanism 26Essen, Louis 53, 55, 62, 65, 163

Ferrel, William 13, 14francium 40Free Atomic Time (EAL) 89, 136French Academy of Sciences 19frequency 34, 42

accuracy 27, 149standards 62, 70, 71, 170,

171

Galilei, Galileo 27geostationary satellite 180Glaze, David J. 76Global Positioning System (GPS)

85, 86, 102, 131–3,136, 141, 154, 178–80

Global Positioning System (GPS,civil applications 155

GLONASS 131, 132, 136, 154,178, 179

GOES satellites 130gram 20grandfather clock 30Grasse 100gravimeter 150gravitational field 150gravitational shift 142–4gravitational waves 149Gravity Probe A 144Greenwich Mean Astronomical

Time (GMAT) 9Greenwich Mean Time (GMT) 7,

8–9, 71, 93–4, 121

Haleakala satellite station 100Halley, Edmond 12, 13, 55, 104

HBG 126Henderson, Dale 164Hewlett–Packard HP 5060A 138–9Hewlett–Packard HP 5061A 144Hewlett–Packard HP 5071A 82, 92Hillis, Danny 161Hipparchus 12Hulse, Russell 149Huygens, Christiaan 28hydrogen 41hydrogen atom 35–9hydrogen maser 82–4, 144hyperfine splitting 84hyperfine states 39, 75

Improved Lunar Ephemeris 62indium 176International Astronomical Union

(IAU) 8, 9, 19, 23, 53,54, 71

International Atomic Time (TAI)70, 71, 80, 86, 89, 109,112, 113, 134, 136,170, 176–80

International Date Line 7International Earth Rotation

Service (IERS) 71,95–6, 109, 111, 179,180

Terrestrial Reference Frame132

International Kilogram 21, 22International Metre 21International Radio Consultative

Committee 71International Space Station 169International Telecommunication

Union (ITU) 71, 154Internet 153

196 INDEX

interplanetary spacecraft 146inversion frequency 42, 45ion-based clocks 172ion trapping 171–2

Kastler, Alfred 2Kelvin, Lord see Thomson, Sir

William (Lord Kelvin)kilogram 20–2, 157–60Kirchhoff, Gustav 33, 35, 84krypton lamp 156Kusch, Polykarp 2

Laboratoire Primaire due Temps etdes Frequences (LPTF)78

LAGEOS 102Laplace, Pierre–Simon 13laser cooling 166laser reflectors 101leap second 71, 95–113, 177–8

insertion 108–13number needed 111–13

Lee, David 76Levine, Martin 144light reflectors 100light waves 44lightning strikes 151local sidereal time (LST) 11Long Now Foundation 161long-wave radio services 126–8Lowe, Andrew 87Lowe, John P. 76LPTF-FO1 79, 80lunar laser ranging 99–101Lunokhod 100Lyons, Harold 41, 42, 43

McCarthy, Dennis 177McDonald Observatory 100

Markowitz, William 55, 57, 59, 61,62, 65

Mars 146mean solar day 20, 22, 25, 104mean solar second 112mean solar time 6, 7, 9Mercury 146mercury ions 171Meteorological Office 151metre 20, 156, 157Milky Way 39Moon 12–15, 55, 56

distance from Earth 100Moon camera 57–62

engineering tolerances 61principle of 60

Moon landing 99Morrison, Leslie 104moving clocks 142–3MSF transmitter 126, 130, 152

National Bureau of Standards(NBS) 41, 43, 64

National Physical Laboratory(NPL) 21, 22, 53, 57,64, 65, 86, 125, 129

NBS-1 75near-infrared light 170neutrons 40Newcomb, Simon 18, 23–4Newton, Isaac 17Newtonian time 17, 19NIST 75, 123, 129, 171NIST-7 75, 76, 78, 135–6NIST-F1 79nitrogen 41Nobel Prize 1noon 4, 6nucleus 38

INDEX 197

optical frequency standards 170optical pumping 75–8optical state selection 76–8optical transitions 176Orion Nebula 11, 36orrery 18oscillator 26

Paris Observatory 132, 180Parry, Jack 62, 163Paul, Wolfgang 2Pavillon de Breteuil 20, 21pendulum clocks 27–30PHARAO 169Phillips, William 2, 166photographic zenith tube (PZT) 97photography 58photons 36, 37, 41, 159, 160, 163,

165, 173, 174Physikalisch-Technische

Bundesanstalt (PTB)72, 74, 127, 138, 149

Planck’s constant 160polar wobble 16position measurement 154–5post-glacial rebound 105Pound, Robert 143precession 12primary frequency standards 72–9,

81, 90Prochorov, Aleksander 2proton 36PSR 1913+16 147, 148PSR 1937+21 181public time signal 122pulsars 146–7, 180–1

quantum jumps 174quantum theory 35

quartz-crystal clocks 32–3, 115,125, 126, 128, 138

quartz-crystal oscillators 32, 85,141

Rabi, Isidor 2, 35radio astronomy 153, 154radio masts 127radio receivers 151radio signals 141, 152radio stations 56radio stations broadcasting UTC

time signals 124radio telescopes 99radio time signals 121–8radio waves 121–8, 146, 147, 151railway clocks 151–2Ramsey cavity 83Ramsey, Norman 2, 83Rebka, Glen 143relativity 142, 145, 146, 148, 159

and time transfer 133–8Romer, Ole 96Royal Greenwich Observatory

(RGO) 54, 63–5, 138,180

Royal Observatory 7, 121rubidium clocks 84–5, 143rubidium 84–5

Sagnac effect 137satellite laser ranging 101–2satellite navigation 131–2, 180satellite time signals 130satellites 136seasonal variations 16–17, 72,

106–8secondary atomic clocks 79–85seismic waves 151

198 INDEX

Shapiro, Irwin 145Shirley, Jon 76short-wave radio services 123–6Shortt clock 30–1, 138Shortt, William 30SI second 65, 89, 108, 112sidereal day 10sidereal time 10sidereal year 23six pips 138–9sodium 33–5solar day 5Solar System 55solar time 3–10sound travel time 117sound waves 44space applications 169–70Space Hydrogen Maser (SHM)

169Speaking Clock 128–9special theory of relativity 142–3speed of light 156–7Spencer Jones, Sir Harold 16spin–flip transition 39stability 27standard time 6–8steering process 92Stephenson, Richard 104Stepped Atomic Time 65Stern, Otto 1, 2strontium 172–5summer time 9surveying 155synchronisation 151–4Systeme International d’Unites

(SI) 23, 157

Tanlaw, Lord 93–4Taylor, Joe 149

Teflon 83telegraph 121telephone systems 152–3telephone time services 128telescopes 153, 154Thomson, Sir William (Lord

Kelvin) 33, 34, 171Thuban 12tidal drag 15, 104tidal friction 13–16time

future 161–81investigations 142

time balls 121time dilation 142, 144time guns 121time intervals 149–51time of vibration 33time scales 25, 86, 89, 108, 149time signals 56, 93, 121, 149

broadcasting 116–17public 122radio 121–8

time transfer 115–39and relativity 133–8common view 119–20one-way 116–18principles 116–20two-way 118–19

time zones 7, 8timekeeping 1Timeline 128timing centres 87, 90Townes, Charles 2tracking stations 169–70travel time delay 117–18tropical year 23, 24Truetime 129

INDEX 199

Universal Time (UT) 8–9, 11, 54,95–6, 101

measurement 96–103US National Bureau of Standards

see National Bureau ofStandards (NBS)

US Naval Observatory (USNO)56, 57, 64, 125, 180

US Naval Research Laboratory 64UT0 54, 93, 96UT1 54–5, 93, 95–103, 108, 109,

111–13UT2 55–7, 61–5, 93, 96, 125UTC 81, 86, 87, 94, 109, 111, 116,

123, 125, 128, 129,138, 151, 176–80

van de Hulst, Henk 39Vega 12Venus 146very long baseline interferometry

(VLBI) 99, 153, 154Vessot, Robert 144

vibration frequency 157visible light 170

Wallops Island, Virginia 130Watt balance 159waveguide 42wavelength 34Whibberley, Peter 164world clock 69–70

accuracy doubts 70drawbacks 69–70

world time 69–94world time scales 70–2world timekeeping 53, 90World Wide Web 129WWV 56, 123–6, 128WWVB 65, 127WWVH 123, 124

ytterbium 173, 176

Zacharias, Jerrold 62, 78