e000MENT RESUEE ED 159 058 SE 024 911 . , p AUTHOR Jpspersen, James; Fitz-Randolph, Jane , TITLE Prot!). Sundiadeto Atomic Clocks: Understanding Tide aqd 'Frequency. INSTITUTION NAional Bureau of Standards (DOC), Washingt, n D.C, . REPORT NO 'NBS-Monogr-155 . At PUB-DATE Dec 77 )7/ NOTE A180p.; Occasional blue print may _.)not reproduce well; J Cartoons on pages 8, 15,16,.-51, 62, 64, 68, 71, 75, 94, 109, 116, 121, 162 deleted dine to copyright restrictions " AVAILABLE FROM Superintendent of Documents, ths;-Governiprit Printing )Office, W hington, D.C.20'402 (Stock Number 003-003-0r650-1;-$4.00) 1 EDRS PRICE MF-$0.83 HC-$10.03 Plus Postage. DESCRIPTORS *Instructional Materials; *Mathematical Applications; *Measurement; Post'SecOndary MI:cation; Reference Materials; *Time- IDENTIFIERS . *Clocks; Timekeeping e- A4 ABSTRACT An introduction to time, timekeeping, and .thee uses of time information, especially in the scientific and technical areas, are offered in this book foi laymen. Historical and p,bilosophical aspects of'time and timekeeping are included. The scie tific-thoug t -on time has been simplified. Contents include: the na u = of time time and frequency4 early man-made clocks, quality f ;Ito ern clocks (quartz, atomic, etc.) modern watches -fetettli- c, quartz-crystal, etc.), time scales, the correct tim i'time signals, standard t4ime, applications oftime, time and mathematics, time and physics, time and astronomy time and automation, time as ,information, and the future of time. (MP) f a a , . *********************************************************************** * ,Reproductions supplied by EDR the best that can. be made *, * , ;2_, frOm the iginal d cument.' , * **V0*-*********44********************* * * * *, ** * * * * # * * * ** * * * * * * * ** 11D5-: ofixqq, 3 X MS.,;,41)14 ATOMIC dILFOCIIK RSTAM U S DEPARTMENT OF HEALTH, FRE OE EDUCATION I WELFARE NATIONAL INSTITUTEOF EDUCATION THIS DOCUMENT HAS BEEN REPRO-' DUCED EXACTLYAS RECEIVED THE PERSON OR FROM ATING IT POINTSORGANIZATION ORIGIN. OF VIEW STATED DO NOR OR,OPINIONS SENT OFFICIAL NECESSARILY REPRE- NATIONAL INSTITUTE,OF EDUCATION POS,ITION,OR POLICY C=1 LU Ne 4 t, NATIONAL BUREOU OFSTANDARDS ATOMIC CLOG 3 FR0M SUNDIALSTo ATOMIC CLOCKS Understanding Time and Frequency N- by. James Jespersen and Jane Fitz7RandoTh Illustrated by John Robb 3. Library of Congress Catalog -Card Npmber: 77=600056 National Bureau of Standards Monograph 155 Nat. Bur. Stand. (U.S.), Monogr. 155,177 pages (Dec. 1977) CODEN: NBSMA6 . 4 0 4 For sale by the Superintendent of Documents, U.S/Goyem nting Office, Woshington, 0.6.20402 Stock No. 003-003-01650-1 Prices $c4 (Add 25 percen tional for other than U.S. mailing). FOREWORD Time and its measurement is, simultaneously, very familiar ands very m sth, rioup. I suspectwe' all believe that the readings of our clocks and watches are somehow related to the sun's' position. However, as science and;technology developed, this relationship has come to be determined bya very complex system involving--,jiist to name a fewastronomers, physicists, electronic engineers, and statisticians. And because .time is both activel3f and precisely coordinated among all of the technologically advanced nations of the world, international orgNa-nizations are also involved. The standard time-of-day radio broadcasts of all countries are controlled to at least 1/1000 ofa second., of each other; most time services, in fact, are cont olled within a very few millionths ofa second! The NationalBureau of Standards (NBS) mouna major effort in developing and maintaining. standards for time and frequency. This effort ten s to be highly sophisticated and perhapseven esoteric at times. Of course, most of the publications generated appear in technical journals aimed at,specidlized, technically sophisticated audiences. I have long-been convinced, however, that it is very importat to provide a descriptive book, addressed to a much wider audience, on the subject of time. There are many reasons for this, and .4-I will give two. First, it isvery simplya fascinatingsubject. Again, we often have occasion to explain' the NBS time program to interested people who do not have a technical- background, and such a book, would be an efficient andhopefully--intereting means informing them. Finally, this book realizes a long-standing personal desire to, see a factual and understandable book on the subjectof time. James A. Barnes' May6, 1677 tI- %.: '''Preparation of this docuntertt.las supported in part by the 1842nd Electronic Engineering Group, Cs/DCS Division,Air Force Communications Contents "t I. THE RIDDLE OF TIME 4 1.- The, Riddle of Time 3 'The Nature of Time/What Is Time ?/Date, Time Interval, and Synchronization/Ancient Clock Watchers/Clocks in Nature/Keeping Track., of the Sun and Moon/Thinking Big and Thinking Small An Aside on Numbers, 2.Everything Swings , a 11 Getting Time from Frequency/What Is a Clock?/The Earth-Sun Clock/Meter-Sticks 'to Measure Time/What Is a Standard ?Mow Time 'Tells Us Where in the World We' Are/ Building a Clock that Wouldn't Get Seasick II. MAN-MADE CLOCKS AND WATCHES 3.Early Man-Made Clocks - 25 Safi(' and Water Clocks/Mechanical Clocks/.The P,endularn Clock/The Balance-Wheel Clock/ Further Refifiements/The-Search for Even Better Clocks. 4. "Q" Is for Quality 31 /- The Resonance Curve/The Resonance Curve and Decay Time/Accuracy, Stability, and Qrnigh Q and Accuracy/High Q and Stability/Waiting to. Find the Time/Pushing. Q to the Limit/Mors about QAn Aside , c 5.- Building Even Better Chicks . 30 The Quartz Clock/Atoniic Clocks/The Ammonia Resonator/The Cesium,Resqnator/One1.! Second in 370,000 Years/Atomic Definition of the Second/The Rubidium Resodator/The : Hydrogen Maser/Can We Always Bultld- a Better Clock? n, '6. The "Correct Time" for! the Man in the Street , 4 Modern MechanicarWatches/Electric and Electronic Watches /The Quart rystal Watch/ch/ ,How Much Does "The Time" Cost? 4 III. FINDING AND KEEPING THE TIME t'41% 7. Time Scales 59 Tie Calendar/The Solar_Day/Thet'' Stellar or Sidereal Day/Earth Rotation/The,,' Continu- ing Search for More Uniform Time: Ephemeris Time/How Long Is a Second ?/"Rubber" Seconds/The New UTC, System andlthe Leap Second/The Length of the Year/The Keel)... ers of Time/U. S.' Tithekeepers/The Bureau International de I'Heure 8. The ClOck behi the Clock 71 Flying C cks/Time on a Radio Beam/Accuracy/Cove e/Koliability/Otheri, Considera- tions/Ot er Radio Schemes 9. The Time Sign Its Way 79 *? Choosin a Frequency /Very Low Frequencies/Low Frequencies/Medium Frequencies/ Higitjrequencies/Very. High Frequencies/Frequencies .above 300 MHz/NoiseAddita- tive and Multiplicative /Three Kinds of Time Signals t C THE USES OF TIME 10.. Standard Time Standarti,Tirne Zones and Daylight-Saving Time/Time as a Standard/Is a Second Really a. Second?/Who Cares about the Time? 11. Time, The Great Organizer 69 . Electric Power/Modern Communication Systems/Transportation/Navigation by Radio Beacons/Navigation by Satellite /Some Common and Some Far-out Useut Time and Fre- quency Technology ,) 1 - , . V TIME, SCIENCE, AND TECHNOLOGY 12. Time" and Matheinati 113 1 Taking. Apart and Putting Together4Slicing up the Past and theFuJe--Calculus/Con- ditions and Rules/Getting at the Truth with Differential Calculus/NeW-ton's Law of Gravi- tation/What's Inside the Differentiating Machine?An Aside 13.. Time and Physics 123 Time is Relative/Time Has Direction/Time Measurement IS Limited/Atomic,and Gravita- tional Clocks/The Struggle to Preserve k Symmetry/The Direction of Time and Time Sym- etriesAn Aside ... '14.Time and Astronomy 135 Measuring the Age of the Universe/The Expanding Universe/Time Equals Distance/Big ..-1\ Bapg or Steady State ?/Stellar Clocks/White Dwarfs/Neutron .Stars /Black Holes/Time Comes to a Stoop/Time, , Distance, and Radio,, Stars L - , -15. Clockwork and Feedback / ----143 A Open-Loop Systems/Closed-Loop Systems/The Response Time/Systent---Magaification or Gain/Recognizing the Signal/Fourier's "Tinker Toys"/Finding the Signal/Choosing a Control System 0 . u 16. Time as Information .k . t 151 . , _ . Three Kinds of Time Inforination Revisited/Geological Time/Interchanging Time and 'Location Information/Time as Stored Information /The Quality of Frequency and Time Information 17. The Future of Time 159 UsiAg Time to Increase, Space/Time and Frequency InforniationWholesale and Retail/ TimgeDissemination/Clocks in the Future/The Atom's Inner Metronome/Time Scales of the Future The Question of LabelingA Second is a Secon, is a Second/Time through the Ages/What Is Time, Really?/Particles Fasterithan Lightl--An Aside a .. ,-.0 PREFACE AND ACKNOWLEDGMENTS .1.... This is a book for laymen. Ioffers an. introdUction_t_a_time, timekeepig,, and. the usev of..time. informa- tion, especially in .the _scientific and_technicalareas, It is impossible, to-consideltirneand timekeeping with out including historical and p ilosophical aspects of the 'subject, liutwe haVe merely dabbled in theSe. We . hope historians and ,philosopiae .swill forgive our shallowcoverage of their important contributions to man's understanding of time, and that scientists will be forbearing, towardou,,, simplified account of scientific. thought on time in the interest of presenting a reasotiably complete view ina limited number of pages. Time is an essential:comPenent in .most disciplines of science ranging from astronomyto nuclear physics. It is also a practical necessity in managing ourieveryday lives, in such obviousways as getting to work on M.!, and ..in countless ways that rlibst persons have never realized, as,ove shall see. Because of the many asSociations of time, we have introduced a ceiCn'uniformityof'language and defi- nition which. the specialist will. realize is .somewhat foreign tehis particular field. Thiscompromise seemed .necessary in a book directed to the general reader. Today the UniteNtates andome parts of the rest of the world are in the process of converting to the metric system ofmeasit ireTent, vhich we. use in this book. We have also used the An Ofinilions of billion and tron; thus, 1000 millien, anda trillion means 1000' billion.