Devlin’s Angle, About Time, 1999, https://www.maa.org/external_archive/devlin/devlin_12_99.html

• What is time?

  • Time as a physical phenomenon – time just happens

  • Our perception of time – psychologically we are aware that time is passing

  • The time that we measure (focus of the article)

• Earliest time measurement device was the sundial, in ancient Egypt (prior to 1500 B.C.)

  • Period of daylight was the basic unit of time

  • Broke the period of daylight, between sunrise and sunset, into 12 equal parts

    • Each hour was just one twelfth of the daylight of that day. Therefore, hours would differ depending on the seasons and place

    • Time could not be measured in darkness

• Other early devices were:

  • Sandglasses

  • Waterclocks

  • Candles

  • Used for measuring the time of an activity

• Early timekeeping devices still adhered to restrictions set by sundials, which were still being regularly used, such as the length of hours changing based on seasons

  • Nighttime hours were calculated as the length of a daytime hour from 6 months before. Eg a July 1st nighttime hour would be the same as a January 1st daytime hour

• Benedictine Monks had regulated prayer hours where a bell would ring to let them know the time

  • Gave us our word for clock; the Latin word for bell was clocca

• Interest on loans, the idea of time making money, was banned in most Christian communities until the 12th century as time belonged to God. This changed after to support a growing money market

• Mechanical time pieces were introduced in 13th century Europe

  • Introduced the idea of measuring time in equal discrete units

  • originally based on a complete revolution of the Earth

  • “o’clock” originally meant “of the clock”, as in according to the clock, because clocks determined a time so different to other methods around then

  • Timepieces require oscillation to work

    • Early oscillating mechanisms were called escapements

    • First escapement was the verge-and-foliot

  • In the 15th century clockmakers used springs to power timepieces instead of gravity

  • In the 16th century Galileo found that the period of a pendulum’s oscillation depends on the dimensions of the pendulum, not the size of the arc

  • In the 17th century clocks were accurate to within 10 seconds

    • It then become possible to measure things like the variation in the sun’s speed

• Time was used to measure longitude when travelling at sea

  • As the Earth rotates a full cycle every 24 hours then every hour it rotates 15 degrees of longitude. This means that for every degree of longitude you travel away from your starting longitude your timepiece will be 4 minutes out (as 60/15 = 4). To calculate your longitude, simply check your timepiece’s time when the sun is at its highest (noon) and calculate the discrepancy

• GMT originated in London as people had to keep adjusting their clocks whenever they travelled one longitude across

  • Cities such as Bristol were 20 minutes out from London so this made timekeeping when travelling annoying, and especially difficult for delivery services

  • The problem became worse with railways in the 19th century

  • Eventually railroads decided to run according to London time

    • Or GMT because London time was determined by the Royal Observatory at Greenwich who used stars’ position at night to measure the Earth’s rotation, and thus time

• America had to implement regional timezones as railroad companies, similarly to London, would use their origin city as their time, resulting in up to 80 different railway timetables being in use

• By 1884 most countries had accepted Greenwich as the base for measuring longitude

  • It became the equivalent of the equator but vertically

  • Liberia, the absolute rebels, didn’t make the change of accepting this common world time until 1972

• UTC, which is administered in Paris, was established when people started using quartz crystals in the mid 20th century in clocks. Quartz crystals could vibrate at a much higher frequency than other devices and so could be used to measure much smaller measurements than a second

  • UTC is based on movements of distant quasars and is called coordinated universal time

• Atomic clocks can have an even higher frequency than quartz clocks, thus making them more accurate to million millionths of seconds

  • They are a caesium atom that has an electron inside, when hit with microwave radiation, will flip its magnetic direction and emit energy with a constant frequency of 9,192,631,770 cycles per second

• The Long Now Clock

  • The clock is a monument to timekeeping that will be accurate for 10,000 years

  • It is required to be maintainable and future generations will be able to keep it working without advanced tools

  • https://longnow.org/clock/

 

 

Rutherford and Fry’s Complete Guide to Absolutely Everything Abridged, 2021

• The pendulum clock was invented in 1656

• In the 17th century the pendulum clock was used to calculate discrepancies between sundials and other timekeeping devices. They found that over the course of the year the sundial had more fluctuations; this was actually because there are fluctuations in the Earth’s rotation during the course of a revolution around the sun. As the planet orbits the star the gravities of other planets slightly change its orbital path.

• In the 17th and 18th centuries scientists decided to redefine the day as an average time representing how long it takes to the earth to spin on its axis for a full rotation every day of the year

  • GMT – Greenwich time

• The H4 pocket watch was invented as a timepiece that was accurate enough to calculate longitude within to within half of a degree when at sea

  • The creator, John Harrison, won a £20,000 cash prize from the English government for developing it

• The Earth’s rotation is slowing down: using fossilized corals scientists found out that 430 million years ago there were closer to 420 days in a year

• Timekeepers in Paris find out the time, according to an equation, once a month and send it out to everyone across the globe. It is then filtered down to everyone else. This is for UTC time

  • A problem here is that Earth time cannot keep up. By the end of the 21st century UTC and GMT will be out by a minute of each other

    • Leap seconds have been implemented to account for this

    • Leap seconds are usually just added randomly or, as is the case for Google, are evenly distributed over the year

• In the 19th century a lady, Ruth Belville, would visit the Greenwich Observatory to get the correct time and sell it to customers across the country. This was before the electronic telegram was able to quickly update people on the time at regular intervals; the two were competing for customers in the mid-19th century

• Our body clocks treat a day as 24 hours and 11 minutes

  • Our bodies adapt and have to regulate themselves to a 24 hour day – this is why we can get very tired and sometimes need an early night

  • A few people have isolated themselves for months on end and always feel that less days have passed than actually have