Time: From Earth Rotation to Atomic Physics

402 Pages·2018·25.297 MB·English

by  Dennis D. McCarthy, P. Kenneth Seidelmann

Cambridge University Press
978-1-107-19728-2 — Time: From Earth Rotation to Atomic Physics
Dennis D. McCarthy , P. Kenneth Seidelmann
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TIME: FROM EARTH ROTATION TO ATOMIC PHYSICS
In the 21st century, we take the means to measure time for granted, without
contemplatingthesophisticatedconceptsonwhichourtimescalesarebased.This
volumepresentstheevolutionofconceptsoftimeandmethodsoftimekeepingupto
thepresentday.Itoutlinestheprogressionoftimebasedonsundials,waterclocks,
andtheEarth’srotation,totimemeasurementusingpendulumclocks,quartzcrystal
clocks, and atomic frequency standards. Timescales created as a result of these
improvementsintechnologyandthedevelopmentofgeneralandspecialrelativity
are explained. This second edition has been updated throughout to describe 20th-
and21st-centuryadvancesanddiscussestheredefinitionofSIunitsandthefutureof
Coordinated Universal Time (UTC). A new chapter on time and cosmology has
beenadded.Thisbroad-rangingreferencebenefitsadiversereadership,including
historians, scientists, engineers, and educators, and it is accessible to general
readers.
dennis d. mccarthy is former Director of Time at the US Naval Observatory
andtheleadingauthorityintheUnitedStatesforastronomicalandtimingdata.He
hasledandbeenamemberofvariouscommissionsandworkinggroupswithinthe
InternationalAstronomicalUnionandhasauthoredandeditednumerouspublica-
tionsdealingwithfundamentalastronomy,time,andEarthorientation.
p.kenneth seidelmann isaresearchprofessorofastronomyattheUniversity
of Virginia and was Director of Astrometry at the US Naval Observatory. He has
ledandbeenamemberofadivision,variouscommissions,andworkinggroupsof
the International Astronomical Union. He has coauthored two other books –
Fundamentals of Astrometry and Celestial Mechanics and Astrodynamics – and
isacoeditoroftheExplanatorySupplementtotheAstronomicalAlmanac.
© in this web service Cambridge University Press www.cambridge.org
Cambridge University Press
978-1-107-19728-2 — Time: From Earth Rotation to Atomic Physics
Dennis D. McCarthy , P. Kenneth Seidelmann
Frontmatter
More Information
© in this web service Cambridge University Press www.cambridge.org
Cambridge University Press
978-1-107-19728-2 — Time: From Earth Rotation to Atomic Physics
Dennis D. McCarthy , P. Kenneth Seidelmann
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TIME: FROM EARTH ROTATION
TO ATOMIC PHYSICS
second edition
DENNIS D. M CARTHY
C
USNavalObservatory(Retired)
P. KENNETH SEIDELMANN
UniversityofVirginia
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Cambridge University Press
978-1-107-19728-2 — Time: From Earth Rotation to Atomic Physics
Dennis D. McCarthy , P. Kenneth Seidelmann
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DOI:10.1017/9781108178365
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Names:McCarthy,DennisD.,author.|Seidelmann,P.Kenneth,author.
Title:Time:fromEarthrotationtoatomicphysics/DennisD.McCarthy(UnitedStatesNavalObservatory
(retired),P.KennethSeidelmann(UniversityofVirginia).
Description:Secondedition.|Cambridge;NewYork,NY:CambridgeUniversityPress,[2018]|Includes
bibliographicalreferencesandindex.
Identifiers:LCCN2018030821|ISBN9781107197282
Subjects:LCSH:Timemeasurements.|Time.|Earth(Planet)–Rotation.
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Cambridge University Press
978-1-107-19728-2 — Time: From Earth Rotation to Atomic Physics
Dennis D. McCarthy , P. Kenneth Seidelmann
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Inhonorofourwives,DianeMcCarthyandBobbieSeidelmann,andourfamilies.
Dedicatedtothescientistswhoprecededusandtaught,mentored,
andinspiredus.
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Cambridge University Press
978-1-107-19728-2 — Time: From Earth Rotation to Atomic Physics
Dennis D. McCarthy , P. Kenneth Seidelmann
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978-1-107-19728-2 — Time: From Earth Rotation to Atomic Physics
Dennis D. McCarthy , P. Kenneth Seidelmann
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Contents
Preface pagexv
1 TimeBeforethe20thCentury 1
1.1 IntheBeginning 1
1.2 CharacterizingTime 1
1.3 Calendars 2
1.4 AstronomicalObservations 3
1.5 Timekeeping 4
1.6 TimeEpochs 5
1.7 TimeTransfer 6
1.8 RotationoftheEarth 7
1.9 Beginningthe20thCentury 8
2 TimefromtheEarth’sRotation 10
2.1 ApparentSolarTime 10
2.2 MeanSolarTime 10
2.3 SiderealTime 13
2.4 WashingtonConferenceof1884 15
2.5 UniversalTime 15
2.6 UT1asMeanSolarTime 18
2.7 CoordinatedUniversalTime 20
2.8 GreenwichMeanTime(GMT) 21
2.9 TimeZones 22
2.10 DaylightSavingsTime 22
3 Ephemerides 25
3.1 EphemeridesandTime 25
3.2 BeforeKeplerandNewton 26
3.3 KeplerandNewton 28
3.4 Tables,GeneralTheories,andEphemerides 29
vii
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978-1-107-19728-2 — Time: From Earth Rotation to Atomic Physics
Dennis D. McCarthy , P. Kenneth Seidelmann
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viii Contents
3.5 LunarTheories 32
3.6 TheAdventofComputers 35
3.7 NumericalIntegrations 35
3.8 ObservationalData 36
3.8.1 RadarObservations 36
3.8.2 LunarLaserRanging 37
3.8.3 SpacecraftObservations 37
3.9 ModernEphemerides 37
3.10 ReferenceSystem 38
3.11 BesselianYear 39
3.12 TimeArguments 40
3.13 AstronomicalConstants 40
3.14 RedefinitionoftheAstronomicalUnit(au) 41
3.15 ArtificialSatelliteTheories 42
3.16 TheoryofRelativity 42
4 VariableEarthRotation 47
4.1 Pre19thCentury 47
4.2 SecularVariation 48
4.3 IrregularVariationsintheEarth’sRotation 50
4.4 EarlyExplanationsfortheVariableRotation 58
4.5 CurrentUnderstandingoftheEarth’sVariableRotation 59
4.6 Consequences 62
5 EarthOrientation 68
5.1 ReferenceSystems 68
5.1.1 CelestialReferenceFrame 69
5.1.2 TerrestrialReferenceFrame 70
5.1.3 IntermediateReferenceSystem 72
5.2 VariationsinEarthOrientation 73
5.2.1 Precession/Nutation 74
5.2.2 PolarMotion 76
5.2.3 UT1 79
5.3 VariationsinEarthOrientation 80
5.4 TransformingbetweenReferenceFrames 81
5.5 DeterminationofEarthOrientation 84
5.6 EarthOrientationData 85
6 EphemerisTime 88
6.1 NeedforaUniformTimescale 88
6.2 DanjonProposal 89
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978-1-107-19728-2 — Time: From Earth Rotation to Atomic Physics
Dennis D. McCarthy , P. Kenneth Seidelmann
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Contents ix
6.3 ClemenceProposal 90
6.4 AdoptionandDefinition 91
6.5 ObservationalDetermination 92
6.6 TheEphemerisSecondandAtomicTime 95
6.7 HistoricalΔT 97
6.8 ProblemswithEphemerisTime 97
6.9 Relativity 100
6.10 DynamicalTimescales 101
7 RelativityandTime 104
7.1 NewtonianReferenceSystems 104
7.2 SpecialRelativity 104
7.3 LorentzTransformations 106
7.4 CoordinateandProperTime 107
7.5 MinkowskiDiagrams 109
7.6 TimeinSpecialRelativity 111
7.7 GeneralRelativity 112
7.7.1 MetricsinGeneralRelativity 112
7.7.2 TheEquivalencePrinciple 113
7.8 IAUResolutions 114
7.9 Timescales 121
7.9.1 InternationalAtomicTime 121
7.9.2 DynamicalTimescales 121
7.10 RelativisticEffectsinTimeTransfer 122
8 TimeandCosmology 123
8.1 Introduction 123
8.2 Space-TimeMetric 123
8.3 TheExpandingUniverse 124
8.4 AgeoftheUniverse 125
8.5 EvolutionoftheUniverse 126
8.6 CosmicTime 126
8.7 Time’sArrow 128
8.8 FutureoftheUniverse 128
9 DynamicalandCoordinateTimescales 131
9.1 ReplacingEphemerisTime 131
9.2 TerrestrialDynamicalTime(TDT)andBarycentric
DynamicalTime(TDB) 132
9.3 ProblemswithTDTandTDB 135
9.4 NewReferenceSystem 136
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978-1-107-19728-2 — Time: From Earth Rotation to Atomic Physics
Dennis D. McCarthy , P. Kenneth Seidelmann
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x Contents
9.5 NewTimescales 137
9.5.1 TerrestrialTime(TT) 138
9.5.2 GeocentricCoordinateTime(TCG) 139
9.5.3 BarycentricCoordinateTime(TCB) 139
9.5.4 TDBRedefined 141
9.5.5 BarycentricEphemerisTime(T ) 142
eph
9.6 ΔTandEphemerisTimeRevised 142
9.7 RelationshipsamongCoordinateTimescales 143
10 ClockDevelopments 148
10.1 Introduction 148
10.2 KeepingTimeinAntiquity 148
10.2.1 ClepsydraeandWater“Clocks” 149
10.2.2 OtherTimekeepingDevices 150
10.3 TheFirstMechanicalClocks 150
10.4 PendulumClocks 151
10.4.1 Galileo 152
10.4.2 Huygens 152
10.4.3 PendulumClockDevelopments 155
10.4.4 Chronometers 156
10.5 QuartzCrystalClocks 157
10.6 ClockPerformance 160
10.6.1 Quality(Q)Factor 161
10.6.2 Precision 162
10.6.3 Accuracy 163
10.6.4 Stability 163
11 MicrowaveAtomicClocks 171
11.1 BeyondQuartz-CrystalOscillators 171
11.2 PhysicsofAtomicClocks 172
11.3 GeneralStructureofAtomicClocks 174
11.4 DevelopmentofAtomicClocks 177
11.4.1 Caesium 177
11.4.2 Hydrogen 189
11.4.3 Rubidium 191
11.5 TrappedIonClocks 194
11.5.1 Mercury 196
11.5.2 OtherIons 197
11.6 PHARAOLaser-CooledMicrogravityAtomicClock 197
11.7 CharacterizingAtomicClocks 198
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