The document discusses the evolution of timekeeping from ancient civilizations to modern times, highlighting various historical calendars, astronomical events, and cultural practices linked to time. It emphasizes the importance of accurate timekeeping for navigation, financial transactions, and technological applications while addressing current debates about the relevance of the leap second. Additionally, it explores the relationship between astronomical phenomena and man-made time systems, underlining the complexities of synchronizing them.

1. What Time IS It? Northern
Colorado
Timekeeping in Ancient & Astronomical
Society
Modern Astronomy
Suzanne Metlay, Ph.D. 2 Feb 2012
Front Range Community College

2. Relating Time to Place:
Moon & Sun
Ishango Bone
 Central Africa: > 20,000 years old
 Marks count moon phases?
Analemma
 Apparent location of Sun at zenith
 Defines seasons

3. Relating Time to Place:
Equinox & Solstice
Native American
Aztec, Incan, Mayan
 Chichen Itza: Spring Equinox
 Machu Picchu: Templo del Sol
Winter Solstice
Anasazi: Chaco Canyon, NM
 Cheyenne: Medicine Wheel, WY
 Pawnee, Chumash, Pueblo, Zuni
Pawnee Star Chart
Newgrange Tomb Entrance, County Meath, Ireland
Winter Solstice at Newgrange Tomb
Week before/after winter solstice,
sunlight penetrates tomb
Swirl patterns on entrance stone
(megalith) represent the Sun?
Entire year’s calendar inside tomb

4. Relating Time to Place:
Newgrange Tomb, Ireland
Megalithic swirls lit by Winter Solstice Sunlight from 3200 BCE

5. Relating Time to Place:
Cross-Quarter Days
What are cross-quarter days?
 Mid-points between seasons
1 Aug: Lammas (aka Lughnassadh)
To honor Lugh, Celtic “god of many skills”, gather berries and 1st harvest
31 Oct: Samhain
Halloween and El Dia de los Muertos
2 Feb: Imbolc
Groundhog Day

6. Relating Time to Place:
Mediterranean Calendars
Why does a circle have 360 degrees?
 Ancient Babylonians: Year = 360 days
 Also gave us 60 seconds/minute and 60 minute/hour
 Ancient Egyptians developed 24 hour day
Lunar calendars count 12 or 13 sets of Moon Phases each year
 Jewish calendar has leap months added in 7 of every 19 years to stay
seasonally adjusted
 Islamic calendar has no adjustments = 354 days
Catholic Church adjustments
 Julian & Gregorian calendars
 Leap days added yet still incorrect
Modern calendars acknowledge disconnect between Earth’s
rotation rate (365.25 days/year), months (28-31 days each), year

7. Calendars: Complete Fiction?
~40 calendar systems currently in use
Samoa skipped Friday, December 30, 2011
 Moved location of
International
Date Line
Changes in dates
= Changes in space
and time
Even best modern calendars need periodic adjustments

8. http://www.universetoday.com/92306/new-year-new-calendar-but-johns-hopkins-scholars-say-we-need-a-permanent-ed

9. Sidereal & Synodic Time
Sidereal Time = Based on actual motions of celestial objects
 From Latin “sidus” = star
 “Stella” also means star, so constellation = group of stars
Synodic Time = Based on what humans see and care about
 Astronomical conjunctions where heavenly bodies are seen
to meet, such as solar eclipse or sunrise over special place
Chankillo: http://www.bbc.co.uk/news/science-environment-12619455
 Linguistically related to ecclesiastical synod, where people meet
regarding heavenly issues
Calendars and clocks are increasingly synodic
 Less emphasis on what is occurring astronomically with
physical bodies such as Earth, Sun and Moon
 More emphasis on atomic timekeeping and virtual
interactions, especially with space-based technology

10. Developing Modern Clocks
Why are longitude and right ascension
measured in hours and minutes?
 Clock of the sky
Who invented the modern clock?
 John Harrison:
http://www.nmm.ac.uk/harrison
What is the most accurate clock?
 Atomic clock
 Cesium-133 electron transitions
 Several clocks to synchronous time
Video - How We Tell Time in 2012:
http://www.bbc.co.uk/news/science-environment-12787502

11. Modern Time Zones

12. Calendar/Clock Reform
Time Zones Map
 Note how lines are shifted to accommodate local interests
 Indiana/Nova Scotia examples
 China – all 1 time zone!
Church efforts at Calendar Reform  Blame the Railways
 Modern calendars are almost entirely synodic now
 Local solar time replaced by whatever clocks say
 Noon not necessarily solar zenith anymore
Geodesy = Mapping of precise positions on Earth
 Changes affect fabric of space-time => gravity wells
 Need to account for these changes – GPS data/timekeeping

13. Geodesy: Linking Time and Space on Earth
“Automated teller machine (ATM) banking and other financial transactions,
voice communication, high-speed computing, and the Internet all depend
on precise timing… GPS clocks, in turn, depend on the precise positioning
derived from NOAA’s National Spatial Reference System.”
-- “Geodesy: Imagine the Possibilities”, National Geodetic Survey, NOAA, 1999 (page 10)
GPS satellites broadcast correct timing information
 0.08 seconds to travel < 15,000 miles to the receiver.
 “Any error in the position of the receiver causes errors in timing.”
Gravity Map of Earth, GOCE, 2011
Fiber optic cable or radio transmissions
 “Every foot of error in the positions of the electronic message transmission and
receiving sites equals one nanosecond of error in timing, increasing the probability of
collision and jamming.”
Kevin Slavin - Stock Market Algorithms (start at 10:45, end at
13:10): http://www.youtube.com/watch?v=TDaFwnOiKVE

14. Nanoseconds Matter
$ Billions depend on timely financial transactions
Defense & commerce needs for accurate timekeeping:
U.S. Naval Observatory Master Clock: Washington, D.C.
 Alternate Master Clock: Schriever AFB, CO
Earthquakes and tides change Earth’s rotation rate
 Who is Earth’s official timekeeper?
 International Earth Rotation and Reference Systems Service:
http://www.iers.org/
 How does the process work? http://www.slate.com/id/2207757

15. IERS & USNO Work Together

16. Which Time System Do You USE?

17. What About the Leap Second?
Leap Second
 Introduced in 1972 to help account for
discrepancy between synodic & sidereal time
 Earth’s rotation is slowing and irregular
 Losing about 2/1000th second per day
January 2012:
Major meeting of the International Telecommunications Union to
determine whether to keep the Leap Second
 US, France, etc. argue NO
 Keeping the leap second disrupts timed systems such as GPS navigation services
and automated financial transactions
 Britain (Greenwich Mean Time) and others argue YES
 Losing the leap second destroys the relationship between atomic/astronomical time
 How bad would be a global leap minute, leap hour, or leap day?
Decision postponed until 2015  Next leap second: 30 June 2012

18. Gravity Probe B:
Using More Precise Timekeeping to Measure
Earth’s Effect on Spacetime
http://www.youtube.com/watch?v=XkAPv5s92z0&feature=related
Earth drags spacetime
 Time itself changes as Earth’s rotation rate changes!

19. Astronomers Help Tell
What Time It Is
Astronomers have always measured:
 What’s on Earth
 What’s in the sky
Astronomers provide data to keep clocks
aligned to how Earth rotates & orbits Sun
Actual shape of gravitationally massive
objects affects how satellites move and
data accuracy
Lives and $$ depend on accurate time
Story of timekeeping will continue…

20. Questions?
THANK YOU, NCAS!!
suzanne.metlay@frontrange.edu
970-204-8228 (voicemail)

21. Trying to Devise a Better Clock
Why Leap Second Should Go:
http://www.slate.com/articles/health_and_science/new_scientist/2011/1
Clocks and relativity:
http://www.economist.com/blogs/babbage/2010/09/optical_clocks_and
NIST Al+ ion clock:
http://www.nist.gov/pml/div688/logicclock_020410.cfm