Don't Panic Geocast

Episode 6 - "What if you calibrated your candles differently?"

February 27th, 2015

Time is a very complex subject that you can devote your entire life to. Today we’ll cover a few of the basics and enough to get your interest up! We’ll see that it’s difficult to know what a second is and how long relative times are, but absolute time is even messier! We also discuss dried coffee and tetris!

Importance of Time (and why it’s on a geology show)

  • It synchronizes the world and our human interactions (need minutes - hours accuracy generally)
  • It allows us to talk about events in a common coordinate system
  • Allows synchronization of scientific measurements and comparison of data sources. This is really important for seismometers for EQ location!
  • Let’s us use GPS! 1 billionth of a second (nano second) error in 1 GPS satellite, GPS receiver is +/- 1 ft to satellite, which is 2–3 feet on Earth.

Early Timekeeping

  • Burning candles in marked cases
  • Hourglass
  • Water powered clocks
  • Pendulum clocks Galileo and Huygens (fancy temperature compensation as well)
  • Video on Galileo

Modern Time Keeping (Atomic Clocks)

  • First clock was ammonia maser at National Bureau of Standards in 1949, but it really wasn’t all that accurate. It was more of a proof on concept device
  • First cesium clock was in 1955 at the National Physical Laboratory (UK)
  • Leads us to the definition of the SI second he duration of 9,192,631,770 cycles of radiation corresponding to the transition between two energy levels of the caesium–133 atom
  • The NIST-F2, a cesium atomic fountain clock, is good to one second in 300 million years. How F2 works is a combination of feedback control loops, lasers, and really cold atoms.
  • Remember, atomic clocks tick away seconds, they say nothing about the hours, minutes, seconds notation we use to write time. We just define a frequency

Leap seconds

  • Can’t predict them far into the future because of irregularities in Earth’s rotation
  • Announced ahead of time in a bulletin by the International Earth Rotation and Reference Systems Service
  • 25 leap seconds since 1972
  • Next leap second is this year! June 30, 2015
  • Real problem in computing, has caused software and GPS hardware crashes/issues before
  • Google smears the second out over a period prior to the leap

Time Standards

There are TONS of time standards, we’re only going to touch on a few. Most are known with highest precision in retrospect!

Solar time

  • Exactly what you would think, it’s about using the sun’s position as a time source. There is the sundial time (apparent solar time) that changes throughout the year, and the mean solar time which is like a clock time.
  • The equation of time represents the difference between the mean and apparent solar day
  • Star clock

International Atomic Time (TAI)

  • A measurement of proper time (it’s a relativity thing)
  • Weighted average of over 400 atomic clocks
  • If there is an error, it isn’t corrected. This makes it into terrestrial time.

Universal Time (UT)

  • This is what we used to call GMT!
  • Based on Earth’s rotation w.r.t different bodies (why there is UT0,UT1,UT1R,UT2,UTC)
  • UT1 is really mean solar time at the equator

Coordinated Universal Time (UTC)

  • Formalized in 1960
  • Adjustments were accommodated by leap seconds starting in 1972
  • Generally considered to be GMT, but GMT isn’t defined/recognized by the scientific community
  • This comes from TAI by accounting for leap seconds!

Epoch time (Unix Time)

  • Epoch time is the number of seconds that have elapsed since 00:00:00 Coordinated Universal Time (UTC), Thursday, 1 January 1970
  • No leap seconds by definition, but implementation is actually messy
  • Stored is an integer (32-bits) meaning that it will run out and roll over on Tuesday 2038–01–19 One second after 03:14:07 UTC, it’s the year 2038 problem.

The Timekeeper Video

Audio after the outro is David Allen


Contact us:

Show - - @dontpanicgeo -

John Leeman - - @geo_leeman

Shannon Dulin - @ShannonDulin