How did people actually record time? I mean, how did they find out the exact duration of a second? Or an hour?

Question

I know they did it with sundials back in the day, but surely it would depend on the position on the sun? What about the people near the poles? Their sundial would be all screwed up.

Answer 1

For most of human existence knowing the approximate length of the day and time of season was sufficient. The hour and second were not discovered, they were made up by people needing to have greater precision in timekeeping. Making appointments by the hour and minute is a recent change in cultural behavior.

Answer 2

Under the International System of Units, the second is currently defined as

“the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium 133 atom.”

This definition refers to a caesium atom at rest at a temperature of 0 K (absolute zero). The ground state is defined at zero magnetic field.

Answer 3

Mankind decided the length of an hour for himself.  There was a need to divide the day into sub-units, and since the Babylonians counted in base twelve rather than base ten, they decided that the day should be divided into twelve hours, with another twelve for the night.

Each hour was then subdivided for convenience.  

Answer 4

The "exact" duration of a second?  Some of the answers give you the old history and mention the "equation of time", but the more modern history is this:  Simon Newcomb and his students studied the motion of the earth, sun, and moon using data from 1750 to 1892.  In 1895 he published "Tables of the Sun", which gave the equations and data to compute the length of each day compared to the average of his data (i.e., the length of the day around 1835).  He was the director of the U.S. Nautical Almanac Office, so he had a lot of resources and people to help him.

His data was so good, that it was used to define the length of the second as a fraction of the year 1900.  This definition was used until the year 1967, when it was officially changed to use atomic time.

Since 1835, the earth has slowed down a bit, so the average day is now about 24 hours and 4 milliseconds.  The rotation speed is carefully studied by international scientists.

Answer 5

Actually, the Egyptians already had, around 3000 years ago, water clocks that were so precise that they could calculate the correction to be made to sundials (what we, today, call the equation of time).

They had discovered that the Sun drifts a bit around its average position (or, from their point of view, that some days were a tiny bit shorter than others).

As one moves up in latitude -- closer to the poles -- sundials do become better instruments:  shadows are longer (more accuracy), even the noon shadow (shortest of the day) is still long enough to draw geometrical figures (to determine true North and the other cardinal directions).  The only thing is to ensure that the gnomon (the stick that casts the shadow) is tilted at the appropriate angle for the latitude.

People did not live that close to the pole.

The idea of dividing units in fractions of 60 is old (Babylonians).  However, the idea of actually measuring time using minutes (1/60 of an hour) and seconds (1/60 of a minute) is rather recent (500 years or so, depending where you lived).

The day had been divided in 12 hours from sunrise to sunset, with another 12 hours added for night (in our civilization, it happened after the Romans got into cultural contact with the Egyptians).

Breaking each of the 24 hours into 3600 seconds gives 86,400 seconds for a day (from this point, day means a period from noon to noon).  The second was defined as 1/86,400 of the average day, as measured over a whole year (to even out the periods when the day is a bit shorter with the other periods when the day is a bit longer).

With the improvements to pendulums and clocks, it was possible to keep track of actual seconds (Galileo tried it about 400 years ago).

Answer 6

the angle it is aligned to and the height of the bit that stick up are altered depending on location.

Answer 7

As the Earth rotates on its axis, so the Sun appears to move uniformly across the sky and if a rod is placed parallel to the Earth's axis its shadow will naturally move uniformly around itself. In other words, as the Sun moves through an arc of 15° in the sky in one hour so will the shadow move at the same rate. This is the principle on which most (but not all) sundials are based, and in fact the same idea is used with telescopes which are then said to be 'equatorially mounted'.

Most sundials have the gnomon lying parallel to the Earth's axis. If the dial plate lies in the equatorial plane then the time scale is equiangular (all the hour lines are exactly 15° apart). If the dial is placed in any other plane then the time scale is no longer equiangular and the angles between the time marks have to be calculated using trigonometrical formulae. Dials can be classified according to the plane in which the dial lies  

Answer 8

Record the date and time on the cover sheet of the data sheets just before you start to make observations.  Record the identification number, species and and time for each observation on the data sheets.  It is usually best to record number, species, and time data before recording the rest of the data (altitude, type of flight,   vanishing bearings, etc.).  Be sure to record the time for any additional  measurements and/or observations that you make, particularly if the migration is light.  Record the time that you finish on the cover sheet.

Two common mistakes to avoid when recording time data are: (1) recording the time as daylight savings time instead of standard time, and (2) failing to record the time for some of the observations.  I avoid the first mistake by not relying on my wristwatch and instead having a separate timepiece set for standard time that is part of the field kit. The second common mistake, failure to record the time for some observations, usually happens when the butterflies are abundant and I get distracted by other migrants before entering the time data for the current observation. The only method I have found to minimize this problem is to practicing good technique and to resist the temptation to work faster just because the butterflies happen to be numerous. Of course, this cautionary note applies to all data entries, not just time data. I hae found that I that can most easily keep pace with the workload when migrating butterflies pass by at the rate of about one every three minutes.