Simple, just look at a clock. Wish it was that easy, lets throw into this as to why time, calendars and etc. It becomes a whole new ball game from there on. The clock has hands and slowly tick forward. One day we run out of time, we die. That simple. Time, the day and seasons has always been with us, most primitive people had some way to measure it and reconcile it all. It may be as simple as when the sun comes up you start your days work.
Time means something different to all of us. To a cook, their main time may be minutes. The farmer, being daylight may be enough and the season. To an electronics engineer one nanosecond (10 minus9) is a long time. For many of us catching the 7:32 to start work at 9 and clocking off at 5 is our lot. Eternity cannot be quantified into something we can understand.
We have and use what is known as the Gregorian calendar, oh yeah, I remember that from school you say.
|Calendar||Introduced||Length of Year (average)||Approximate Error|
|Gregorian||1582 AD||365.2425 days 27 seconds||1 day every 3236 years|
|Julian||46 BC||365.25 days 11 minutes||1 day every 128 years|
|365 day||Ancient||365 days||6 hours/year (1 day every 4 years)|
According to the Gregorian calendar (which is in use today) the year is intended to be of the same length as the cycle of the seasons. However, the cycle of the seasons, technically known as the tropical year, is approximately 365.2422 days. Since a calendar year consists of an integral number of whole days, a calendar year cannot exactly match the tropical year. If the calendar year always consisted of 365 days, it would be short of the tropical year by about 0.2422 days every year. Over a century, the calendar and the seasons would depart by about 24 days, so that the beginning of spring in the northern hemisphere would shift from March 20 to April 13
The earth doesnt spin on a true north/south pole axis. Its actually tilted at between 22 1/2 and 24 degrees. It goes through a complete cycle once every 24,000 years. How does this impact us? Very simple, where we now know winter in the northern hemisphere and summer in the southern hemisphere this is reversed every 12,000 years. There is climate change for you.
We have established that in spite of a high degree of accuracy the Gregorian Calendar isn’t perfect and will get out of sync eventually and corrections have to be put in place. We have leap years to try and help sort that out. Even that isn’t perfect.
There is a leap year every year whose number is perfectly divisible by four – except for years which are both divisible by 100 and not divisible by 400. The second part of the rule effects century years. For example; the century years 1600 and 2000 are leap years, but the century years 1700, 1800, and 1900 are not. This means that three times out of every four hundred years there are eight years between leap years. When Pope Gregory XIII instituted the Gregorian calendar in 1582, the calendar was shifted to make the beginning of spring fall on March 21 and a new system of leap days was introduced. Instead of intercalating a leap day every fourth year, 97 leap days would be introduced every 400 years, according to the rule given above. Thus, the average Gregorian calendar year is 365.2425 days in length. This agrees to within a half a minute of the length of the tropical year. It will take about 3300 years before the Gregorian calendar is as much as one day out of step with the seasons. There you have it.
Time is equally complex and has its own set of rules. Ever think as to how the worlds time is kept track of? No it isn’t your local radio station or the town hall clock. Without some kind of “standard” we would be in a mess. Everything has a standard, even a one kilo weight. If we didn’t have these we would be in a mess. Yes the one kilo standard weight is affected by gravity which varies all over the world. We wont go into that but suffice we stick with time. Some-one, somewhere in the world is the official time keeper and sets the worlds standard which by agreement is used everywhere. Yes Governments can agree on some things.
Its actually an atom.
What Is International Atomic Time (TAI)?
International Atomic Time (TAI) is one of the main components of Coordinated Universal Time (UTC), the time scale used to determine local times around the world. It tells us at which speed our clocks should tick.
TAI Keeps the Pace
Two components are used to determine Coordinated Universal Time (UTC):
- International Atomic Time (TAI) is a time scale that uses the combined output of some 400 highly precise atomic clocks. It provides the exact speed at which our clocks tick.
- Universal Time (UT1), also known as astronomical time, refers to the Earth’s rotation. It is used to compare the pace provided by TAI with the actual length of a day on Earth.
How is TAI Measured?
International Atomic Time is an extraordinarily precise means of time-keeping. Atomic clocks deviate only 1 second in up to 100 million years.
The secret to this impeccable precision is the correct measurement of the second as the base unit of modern time-keeping. The International System of Units (SI) defines one second as the time it takes a Cesium-133 atom at the ground state to oscillate exactly 9,192,631,770 times.
Atomic clocks are designed to detect this frequency, most of them today using atomic fountains; a cloud of atoms that is tossed upwards by lasers in the Earth’s gravitational field. If one could see an atomic fountain, it would resemble a water fountain.
To achieve the highest possible level of accuracy, the International Bureau of Weights and Measures combines the output of about 400 atomic clocks in 69 national laboratories worldwide to determine TAI. The time scale is weighted, prioritizing the time signal provided by institutions that maintain the highest quality of primary cesium.
Why Use UTC – Not TAI?
The high level of precision achieved by using atomic clocks is both a blessing and a curse. On the one hand, accurate time-keeping is a necessity, for example for time-sensitive technology, such as modern air traffic control systems that rely on satellite navigation.
On the other hand, TAI does not take into account the Earth’s slowing rotation, which determines the length of a day. For this reason, TAI is constantly compared to UT1. Before the difference between the two scales reaches 0.9 seconds, a leap second is added to UTC.
Where is the atomic clock?