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

Author: John Leeman and Shannon Dulin
Published: Fri 27 Feb 2015
Episode Link: https://www.dontpanicgeocast.com/6

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

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