Metlay What Time Is It 2 Feb2012
21
Suzanne Metlay, Ph.D. Front Range Community College What Time IS It? Timekeeping in Ancient & Modern Astronomy Northern Colorado Astronomical Society 2 Feb 2012
-
Upload
western-governors-university -
Category
Documents
-
view
565 -
download
0
description
Presented by Suzanne Metlay (FRCC Faculty) to Northern Colorado Astronomical Society and FRCC students in Fort Collins, CO, on 2 February 2012.
Transcript of Metlay What Time Is It 2 Feb2012
Suzanne Metlay, Ph.D.Front Range Community College
What Time IS It?Timekeeping in Ancient &
Modern Astronomy
Northern Colorado AstronomicalSociety
2 Feb 2012
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
Relating Time to Place: Equinox & Solstice
Winter Solstice at Newgrange TombWeek before/after winter solstice, sunlight penetrates tomb Swirl patterns on entrance stone (megalith) represent the Sun? Entire year’s calendar inside tomb
Native AmericanAztec, Incan, Mayan
Chichen Itza: Spring Equinox Machu Picchu: Templo del Sol
Winter SolsticeAnasazi: Chaco Canyon, NM Cheyenne: Medicine Wheel, WY Pawnee, Chumash, Pueblo, Zuni
Pawnee Star Chart
Newgrange Tomb Entrance, County Meath, Ireland
Relating Time to Place:Newgrange Tomb, Ireland
Megalithic swirls lit by Winter Solstice Sunlight from 3200 BCE
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 harvest31 Oct: SamhainHalloween and El Dia de los Muertos2 Feb: ImbolcGroundhog Day
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
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
http://www.universetoday.com/92306/new-year-new-calendar-but-johns-hopkins-scholars-say-we-need-a-permanent-edition/#more-92306
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 placeChankillo: 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
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
Modern Time Zones
Calendar/Clock Reform
Time Zones MapNote how lines are shifted to accommodate local interests Indiana/Nova Scotia examplesChina – all 1 time zone!
Church efforts at Calendar Reform Blame the RailwaysModern calendars are almost entirely synodic nowLocal 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 wellsNeed to account for these changes – GPS data/timekeeping
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.”
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
Gravity Map of Earth, GOCE, 2011
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/
IERS & USNO Work Together
Which Time System Do You USE?
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
Gravity Probe B:Using More Precise Timekeeping to Measure
Earth’s Effect on Spacetimehttp://www.youtube.com/watch?v=XkAPv5s92z0&feature=related
Earth drags spacetime Time itself changes as Earth’s rotation rate changes!
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…
Trying to Devise a Better Clock
Why Leap Second Should Go:http://www.slate.com/articles/health_and_science/new_scientist/2011/12/leap_seconds_and_the_problem_with_the_global_time_standard.html
Clocks and relativity: http://www.economist.com/blogs/babbage/2010/09/optical_clocks_and_relativity
NIST Al+ ion clock: http://www.nist.gov/pml/div688/logicclock_020410.cfm
