Time

Created Saturday 29 June 2024



What is Time?



Almanac

Different time standards used on the Almanac Page.
Siderial time or angle expressed in Hours, minues and seconds is a system whereby astronomers can locate celestial objects in the sky and is based on the time it takes the Earth to rotate to the same direction in space with reference to distant stars (as opposed to the Sun ) which is aproximatly 23 hrs 56 mins. Siderial time and Greenwich Mean time are aproximatly equal at the Autumn Equinox and siderial time will gain about 4 minutes each day throughout the year so each year there is one extra siderial 'day' compared to the number of solar days.


Greenwich Mean Time GMT, is the average (mean) solar time at the Greenwich Meridian 0° longitude. Until 1972 GMT was the International civil time standard, this has now been replaced with UTC (Universal Coordinated Time).


Local Mean Time is the average (mean) solar time for your local meridian, your longitude(0.0083°) will determine if you are ahead or behind your timezone by a factor of 4 minutes per degree, locations further West are behind.


Prior to the coming of the railways, most major towns adopted local mean time, which was dependant on their longitude so Penzance local time was 22mins later than Greenwich, this caused problems with the railway timetables, to solve the problem local clocks were set from the railway train guards watch so all of the UK started to use Standard time (GMT) also called 'railway time'.


Apparent Solar Time is based on the rotation of the earth and the position of the sun in the sky with respect to the local meridian. This is the time as shown on a sundial, and is represented on the clock above by the orange hand. This is the oldest method of timekeeping dating back over 5000 years to egyptian times.
Today in Greenwich apparent solar time is offset from BST by -63:00.


The difference between Apparent Solar Time and Local Mean Time can vary by as much as +- 16 minutes throughout the year, this is known as the Equation of time, and is due to the tilt in the earth's axis and eccentricity of the Earth's orbit around the Sun.
The length of a solar day, the time between two successive solar noons varies from 24h 30s in December to 23h 59m 39s in September.




Equation of time graph



Calendar

This is based on the Coligny calendar found in France (Roman Gaul) in the 2nd century CE with the following assumptions:
The starting date, or Epoch is set at October 17 HE (Holocene era), and is restarted every metonic cycle.
How did i arrive at this date? - as this calendar is almost certainly over 2000 years old i wanted to reflect that in the Epoch, so a fitting timescale is the Holocene era, 10000 years before 1 CE, so i took the start year of the latest metonic cycle (2025) added 10000 years to get the Holocene year (12025) minus 632 metonic cycles (632 * 19 = 12008) and got to the year 17 HE, this of course is completely irrelevant, the important date is the start of the current metonic cycle.
This means the latest metonic cycle starts on 29 Oct, 2025, chosen because it is the first quarter moon closest to 29 October and gives an even spread around that date.


The months start on the first quarter moon, this is because this is the most accurate phase to ascertain and is visible at sunset in Europe (the time of the start of a new day)
The year starts around the time of the Fire festival 'Samhain' between mid October and mid November. so the earliest start of the year is 14 Oct and the latest 13 Nov.
The dates for the Celtic 'Fire' festivals are not fixed by the Gregorian calendar dates, instead are tied to the first quarter moon phases.
Samhain is the first Quarter moon following a full moon after the Autumn Equinox.
Similarly, Beltain is the first Quarter moon following a full moon after the Spring Equinox.
Imbolc and Lugnasa are both three lunar months after Samhain and Beltain respectively.
These dates are sometimes referred to as 'Quarter days', however they are not the same as the old English Quarter days when rents were due and servants were hired.
We must remember that when this calendar was first produced, it was devised only from observations of the sun and moon so starting days needed to be easily determined, the day of the equinox was easy to determine as the sunset is directly opposite sunrise.
The calendar is based around the metonic moon cycle which lasts 19 years, or 235 synodic months, it has 12 standard months (moon phase) each year with an added intercalary month every 2 1/2 years to keep alignment with the solar year.


History

Early humans experienced the passage of time with simple definitions:
Day: Progressed from Night, Sunrise, High Noon, Sunset, Night
Months (Moon): The changing phases of the moon, New , First Quarter, Full, Last Quarter, New
Year: The passing of the seasons, Winter, Spring, Summer, Autumn, Winter
Early Humans had no need to measure time to any great accuracy as they were Hunter gatherers and later settled to become Farmers and everything revolved around the natural rhythms of animals and plants.


When humans started to organise their days for the purpose of commerce or religion, it became necessary to divide the days and years into a more formal arrangement, so the first calendars and clocks were devised.
The first clocks were based on the position of the sun in the sky and used its shadow to indicate the 'Time' of day, this was the sundial, at night the positions in the sky of known stars were observed.
It was the ancient Sumerians who first divided the day and night into 12 periods each, the length of each period varied depending on the season, in summer there is around 14 (modern) hours of daylight and in winter only 10 hours.
This problem got even more exaggerated the further you were away from the equator, inside the arctic circle you can experience up-to 24 hours of daylight in the summer and zero in the winter.
Early Egyptian scholars discovered that at the equinoxes when day and night are of equal length, the sun moves by 15 degrees in 1/12 of the day, so sundials were marked with 'Hours' at 15 degree intervals so each hour became a fixed duration.



Epoch

An epoch is the starting reference point for the measurement of time or date.
Notable Epochs:
Clock time: Midnight 00:00
Julian Day: started in 4713 BCE, a date at which three multi-year cycles started (which are: Indiction, Solar, and Lunar cycles) and which preceded any dates in recorded history and ends in 3268CE.
Unix time: 1st Jan 1970 @ 00:00
Rata Die: 1st Jan year 1, Count of days of the Common Era
Lilian date day 1 = October 15, 1582, The start of the Gregorian Calendar.
Anno Mundi, AM: started on 6 Oct 3761 BCE - Year of the world as devised through creation myths
Holocene Era, HE also known as Human Era, Add 10,000 to CE year number ie. 2024 CE = 12024 HE, HE uses the "beginning of human era" as its epoch, arbitrarily defined as 10,000 BC and denoted year 1 HE



Julian Calendar

The Julian calendar was proposed in 46 BCE by (and takes its name from) Julius Caesar
This was a calendar with 365 days in a normal year and introduced an extra 'leap' day every 4 years to correct for the earths orbit of 365 1/4 days, However this proved to be an over simplification of the actual 365.2422 days.
So by 1545 the calendar was out of sync with the solar year due to adding more than required leap days, so Pope Gregory XIII commissioned a revised calendar to correct the error.
The motivation for the adjustment was to bring the date for the celebration of Easter to the time of year in which it was celebrated when it was introduced by the early Church.
Not all country's adopted the new calendar immediately, some as late as 2016, England adopted the Gregorian calendar on 3 September 1752 when 11 days were removed and the calendar went from 2nd Sep (Julian) to 14th Sep (Gregorian)
Apparently this caused some rioting amongst the population demanding the return of the 11 days.


Hour

originally, 1/12th of the time between sunrise and sunset.
The time it takes the sun to traverse 15 degrees of Longitude.


Minute

adjective:
meaning very small


noun:
60th part of an Hour (1st Minute - Small part)
60th part of a Minute ( Second Minute)


Why 12 & 60?
duodecimal, base 12, traces it's origines back to counting in multiples of 12 as can be counted on one hand using the thumb to count the number of segments on each finger.
Sexagesimal, also known as base 60, is a numeral system with sixty as its base.
It originated with the ancient Sumerians in the 3rd millennium BC, was passed down to the ancient Babylonians, and is still used—in a modified form—for measuring time, angles, and geographic coordinates.
It can be counted using two hands, 0-12 on one hand and 5 x 12 on the other (12, 24, 36, 48, 60)




Different time standards


In ancient times when sundial's were the common method of telling the time, Noon or 12 O'Clock was when the sun was at it's highest point (High Noon) when it crossed the local meridian, this of course was dependant on where on earth you lived, This is referred to as 'Local Solar Time' (LST) and as people did not travel great distances this was not a problem.
After the invention of mechanical clocks, which were only affordable to the rich, or public clocks on churches Etc. it was found that LST and the time shown in the clock can be different by as much as -14/+16 minutes depending on the time of year.
This is because the clock measures time at a constant rate and the sun's position in the sky is dependant on the tilt of the Earths axis and the non circular orbit around the sun, due to the length of a day, the time between to successive solar noon's is not exactly 24 hours and can vary between 23:59:40 and 24:00:30, the clock measures the Local MEAN Solar Time, or LMT. This difference can be calculated using the Equation of Time.


Most places in England used Local Mean time to set the clocks, this was fine as long as you didn't go far from home, However after the building of the railways, people started travelling more and using railway timetables to catch the trains, this proved to be problematic as different towns were all on different times, so if you travelled from London to Penzance the local times were 22 minutes apart!!


To combat this in 1847 the railways adopted London time as the standard and was shown on all railway station clocks, initially the clocks were set from the train guard's watch from London time, but after the invention of the Telegraph the railways would set the clocks from time signals sent via telegraph from London, This became known as 'Railway Time'. By 1855 most of the UK had adopted GMT (Greenwich Mean Time) as the standard, this was not legally recognised until The Interpretation Act 1978



Time Zones

Each country has decided to adopt one of the 26 time zones around the world, this is so the the local Civil time is closely matched to Local Solar Time which helps the population synchronise to the natural circadian rhythms, some country's are so large that different parts of the country are on different time zones, others use one time zone for the whole country (China). Each timezone is separated by approximately 15 degrees Longitude and are mostly set at 1 hour intervals.
This allows the population of a single country to synchronise there daily activities, but if you travel to another country or communicate via telephone or email then you have to allow for the different time zones.


UTC

If you are trying to co-ordinate activities across different time zones then some confusion can occur, so, organisations such as airlines, military, space travel and astronomy use a global timezone known as UTC or Coordinated Universal Time, this is independent of timezones or daylight saving time, it is the same time as GMT. Prior to the adoption of UTC, GMT was the standard world time but is now a timezone identifier just as CET, EDT Etc.



Daylight Saving Time

As if it is not confusing enough to deal with different timezones, some country's in the world (North America & Europe) change their clocks by +1hour during the summer months, this gives the impression of an extra hour of daylight for outdoor activities in the summer, this of course is not true as it does not increase the number of daylight hours but simply fools people into getting up an hour earlier so they see more of the available daylight. To add even more confusion the dates on which the change occurs is different for each country.
There are many arguments for and against daylight saving time, but it just adds more confusion, for instance, some states in the US have different rules for different parts of the same state!!


In the future as the people become more globalised i can see more people adopting UTC as an everyday timezone, this will make coordinating events across the globe less confusing, the only down side is that people will need to retrain their minds to work with different times, High noon will no longer be at 12:00 in most of the world and people won't get up at 07:00 and go to bed at 23:00.





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