Measuring Time
Humanity’s longstanding quest to record and
measure time has moved past keeping track of months and years
and into the realm of keeping track of nanoseconds and beyond.
Our ability to determine who wins an Olympic event by a fraction
of a millisecond often seems to overshadow the fact that we are
still recording millennia events, like global warming, as well.
The advent of time zones has enabled us to formally acknowledge
that it is not the same time everywhere in the world all at
once. Because of the way the earth rotates on its axis, when it
is morning in the western hemisphere, it is evening in the east;
today is someone’s yesterday at the same time it is someone
else’s tomorrow. Various time standards have been established to
homogenize how time is handled on a global scale. Time has been
organized in different ways, some based upon the actual movement
and location of the earth, while others are based upon man’s
interpretation of it. No matter which system of measurement we
adhere to, adjustments will need to be made occasionally to keep
it all in sync. Currently a mixture of leap years, the less
known leap seconds, and in some places, daylight savings time,
helps compensate for the natural wavering of the system we
record. These units, time zones, time standards, and even the
necessary exceptions to time measurement all play a unique role
in forging the perception of time we have today.Measuring time - Common Units of Time“To fill the hour, that is happiness; to fill the hour, and leave no crevice for a repentance or an approval.”Ralph Waldo Emerson As calendars become more organized and clocks more precise, new units of measure are continually being added to the list of ways that we use to describe the passage of time. In the beginning, units were measured strictly by observing the behaviors of solar bodies – the earth, the sun, and the moon – and recording the time associated with their cyclic patterns. Now we can, if we so choose, break away from the limitations imposed on us by our solar system, and record time in ways that we find more appropriate, whether they correlate with the movement of celestial bodies all about us or not. A Year, in its simplest form, is the amount of time that it takes for the earth to revolve once around the sun. Specifically, a year is three-hundred-sixty-five days, six hours, nine minutes, and 9.54 seconds. Therefore, a year is not exactly three-hundred-sixty-five days nor is it quite three-hundred-sixty-six. As it turns out, there are actually a number of ways to define a year. Although the above definition is the one most commonly used, it is actually the definition of a sidereal year – the time it takes the earth to rotate about the sun, relative to the stars. A Tropical year on the other hand, measures the time between two vernal equinoxes, or the moment when the sun seems to be crossing the equator. Its length is three-hundred-sixty-five days, five hours, forty-eight minutes and forty-six seconds. Other commonly used definitions of a year include: anomalistic year, eclipse year, and solar year. According to the calendar of the French Revolution, a decade in those days was ten days long. Today, a decade is a ten-year period, a century is one hundred years, and a millennium is one thousand years. There have traditionally been two different viewpoints concerning when a century or millennium ends. The Gregorian calendar does not technically have a year zero, and so counting really begins in the year 1 AD. In that fashion, the third millennium began on January 1st, 2001, because the first millennium would have begun in the year 1 AD and the second would have begun in 1001 AD. Popular opinion, however, states that a new decade, century, or millennium begins when the “zeros” roll over, and therefore 1990 – 1999 is considered a decade, 1900 – 1999 is considered a century, and 1000 – 1999 is considered a millennium, with the next one beginning on January 1st, 2000. Though not as commonly used, a score is a measurement of two decades, or twenty years, and a lustrum is a way to describe half a decade, or five years. The month is another naturally occurring unit of time. Astronomers began quantifying this span of time while they observed the moon cycle through its phases. One month is the time it takes the moon to circle the earth and pass through all of its phases. Though the concept of a month takes on religious overtones in some eastern religions, in the west it is simply considered to be a convenient way to divide the year and seasons. Its artificial counterpart is the quarter. A quarter, or three months, is primarily used to divide the fiscal year into four manageable parts for the purpose of calculating profits, losses, and taxes. The week, though certainly common in today’s society, stems from the habits of man. The seven-day week seems to have Jewish origins, the seventh day being significant for its mystical meaning in relation to the Holy Sabbath. Other cultures defined weeks spanning from four days to as long as ten days, whatever was a suitable interval between market times. Somehow, the seven-day week stuck. From there, the fortnight, or measurement for two weeks, (fourteen days) was established. The day is the smallest unit of time that still derives its real meaning from the earth's rotation. A day, or the amount of time it takes for the earth to rotate once on its axis, has always been the most useful and direct way to monitor the passage of time. From there, time has been divided into increasingly smaller increments; the day is split into twenty-four hours, the hour into sixty minutes, and the minute into sixty seconds. Work days, lunch hours, and bed times are all regulated by the hour, despite the fact that it is an entirely man made concept and has been interpreted differently over time within different societies. The French divided the day into ten hours rather than 24 in the late seventeen hundreds. Prior to hours, tides were the time indicators of choice. The minute really came into play around the time of the industrial revolution when work shifts and train schedules needed detail. Prior to that, clocks had no minute hand. The second is the base unit of time in the International System of Units, and the commonly known equivalent of one sixtieth of a minute. From microseconds, or millionths of a second, to nanoseconds, billionths of a second, the universe seems to be getting smaller as we endlessly hone in on the smallest moments of life as time passes by. A moment, on some Arabic calendars, denotes one sixtieth of a second in the same way that a second denotes one sixtieth of a minute in English time. How difficult it must be to capture the essence of a moment. Perhaps one of the most abstract units of time in general use today is the concept of a generation. It is often though of as being synonymous with era or more specifically, the lifespan of a person and his siblings. The greatest generation, the postwar generation, generation x – all of these refer to people born roughly within thirty years of each other who are thought to share the same values and ideals, and have experienced the same hardships. Although equally applicable to plants and animals, the relationships between generations in humans, and the feeling of coexistence that members of one generation feel with each other as well as with past and future generations, helps to mold the human existence into one of tradition and culture. Measuring time - Time Zones“Don’t worry about the world coming to an end today. It’s already tomorrow in Australia.”Charles Schultz For a long time, most people kept time simply by taking note of the position of the sun. Hence, sundials were really man's first form of clock, allowing people to harness a resource that had, in actuality, always been available. Even as late as the 1800’s, people still looked to the sun to set their clocks noting that noontime occurred whenever the sun was directly overhead. This of course caused an infinite number of individualized notions as to what the exact time was. Eventually towns organized themselves to the point where neighboring towns had a unified time keeping system. Still, for many reasons, including political wrangling and irregularly shaped borders, discrepancies and subsequent squabbles continued to exist in many areas. Railroads were the main means of transportation in the United States at the time and they provided timely transport between cities. However, what travelers encountered were things like “twenty-seven different time zones in Michigan, thirty-eight in Wisconsin, twenty-seven in Illinois, and twenty-three in Indiana” (Burns). The fact that these states were so close to one another and had so many different mini-time zones between them, arriving or departing on time was a constant problem for commuters and travelers alike. Something had to happen and Britain led the way in 1840 when one of its railway systems (Great Western Railway) agreed to accept London Time as the standard time throughout its route. The benefits of such standardization soon became apparent and in 1847, the industry standards body in England recommended that all railroads throughout the country adopt GMT: Greenwich Mean Time. England is the location of the Prime Meridian and the Royal Observatory, from which all time zones around the world are currently measured. Built in 1675, the Observatory’s original purpose was to track longitudinal lines for the purpose of helping sailors navigate, framing the forerunner to the concept of time zones. With the guidance of Charles Dowd and William F. Allen, the United States adopted a system of four time zones on November 18th, 1883. This meant that individual communities would no longer set their own times. Instead, times throughout the country would be set along imaginary, geographical lines that run from north to south called longitudinal lines. Nowadays, West European Time, also known as Universal Time, is the standard that all time zones around the world are compared to. Since it is the point of origin, all areas that don’t share this time zone are referred to as having plus or minus a certain number of hours in relation to it. Central European Time is “+1” hour, Moscow Time is “+3”, and Tokyo Time is “+9”. In the United States, there is the Atlantic Standard Time (“-4” hours), Eastern Standard Time (“-5” hours), Central Standard Time (“-6” hours), Mountain Standard Time (“-7” hours), and Pacific Standard Time (“-8” hours). The following link will take you to a chart of the standard time zones of the world. http://www.cqham.ru/images/time_zones.gif Separate time zones make sense because the sun cannot be overhead (high noon) at the same time everywhere around the world. At any given moment, times are different at different locations around the globe. Time zones help standardize the process of logging these time changes. In the end, however, time zones are a political policy, and therefore it is individual countries that handle their implementation. Thus there are many unique situations world wide when it comes down to how a time zone is implemented within a country. Here are a few facts about time zones that stick out. 1. Differing time zones meet at the intersection of Finland, Norway, and Russia, causing many towns that are very close to one another to have differing times. 2. China has the widest spanning time zone in the world. It is also the largest country that is under one time zone. 3. Australia has three time zones: Eastern, Central, and Western. Some of the districts within these time zones have begun to implement daylight savings time, while others have not which means that Australia’s time zones sometimes overlap. The following link will take you to a chart of the differing time zones in Australia. http://www.search.com/reference/Time_in_Australia 4. Russia currently has the largest number of time zones, with a total of eleven, followed by the US and Canada, both with six. The following links will take you to a chart of the differing time zones in Russia, the United States, and Canada. Russian Time Zones www.gotorussia.com/travelers_essentials_time_zones.htm United States Time Zones www.timetemperature.com/tzus/time_zone_boundaries.shtml Canadian Time Zones www.timetemperature.com/tzca/canada_time_zone.shtml Measuring time - Time Standards“The solar system has no anxiety about its reputation.”Ralph Waldo Emerson There are many natural phenomena at work about us that we have combined in a way to help us tell time. Many, such as the earth' s orbit about the sun or the spin of the earth about its axis, are irregular and beyond our control. This makes the job of measuring time all the more complicated and, in the past, imprecise. Up to now, as long as there have been calendars based on the location and movement of the earth, moon, sun, and stars, there have been problems recording accurate time that could not be overcome. In an attempt to make order out of this chaos, many different time scales, or time standards, have been created. Sidereal time is a time standard that is based upon the length of time it takes the earth to complete one rotation on its axis relative to a given star. That is, it is the interval between the moment when a star appears at a point in the sky and the moment when it appears at the very same spot once again. This time interval measures approximately 4 minutes less than a normal 24-hour day. Solar time, on the other hand, takes note of the position of the sun rather than the position of the stars to tell the time. Under this standard, a day has passed when the sun returns to the same point in the sky two consecutive times. The length of a solar day is not always constant, but varies. This is due, in part, because the earth's rotation about the sun follows an elliptical orbit rather than a circular one. This means the earth travels faster when it is closer to the sun in its orbit than it does when it is further away. Greenwich, England is the starting point from which we define both time and place. Place because it is the town that the Prime Meridian goes through. The Prime Meridian is the imaginary, 0 degree longitude line that goes from the North Pole to the South Pole separating East from West. Greenwich is also the origin of time as we know it because it is the point on the earth where all other time zones are measured from. This established time scale is called Greenwich Mean Time (GMT) and is based on the mean, or corrected time with respect to the Prime Meridian. In 1928, the name GMT was changed to Universal Time (UT) in order to better reflect its universal acceptance as the world’s civil-time keeping standard. Today both GMT and UT are used interchangeably today. Because UT is affected by the rotation of the earth, UT and its variants are not uniform time scales. To compensate for this, we now base our world time on Atomic time. Atomic time is not directly related to the movement of the earth or moon, but rather is measured in oscillations of the element cesium and is accurate down to a nanosecond, or one billionth of a second. Since atomic time is exact, and earth time is not, a new time scale called Coordinated Universal Time (UTC) was designed to meld the two. UTC is based on Atomic time but is constantly being adjusted to stay within .9 second of UT. Occasionally, we have to add a leap second to keep the UTC fully in synch with the UT. UTC is presently used as the basis for global time scales, the one that the world sets its clocks to. Unlike standards which are based on the rotation of the earth about its axis, there are other standards based on the rotation of the earth around the sun. In the early 1950’s, people began to realize that a day measured by the earth’s rotation about its axis was too inaccurate to be used any longer. They figured that the earth’s rotation was neither smooth nor consistent and any sort of time unit derived from it could not possibly be accurate. To resolve this issue, the International Astronomical Union adopted the Ephemeris Time scale in 1952. This standard measured a second as a fraction of a year (as a fraction of the earth’s rotation about the sun) rather than of a fraction of a day (as a fraction of the earth’s rotation about its axis). The only problem with this is that the gravitational pull of the sun causes the earth’s orbit to shrink. This makes the earth go around the sun a bit faster each year which means that each consecutive year is shorter than the last. So by the late 1970’s the timekeepers once again realized that the current system in place could not be maintained. Therefore, in 1979, the Ephemeris Time standard w replaced with 2 other standards: Barycentric Dynamical Time and Terrestrial Dynamical Time. Terrestrial Dynamical Time (TDT) takes into consideration Einstein’s Theory of relativity and measure’s time based on both Earth’s position and motion. Barycentric Dynamical Time (TDB) on the other hand bases its measurement on time at the center of our solar system. Terrestrial Dynamical Time is nearly synonymous with International Atomic Time (TAI); they’re only 32 seconds apart from one another. International Atomic Time is calculated using hundreds of atomic clocks in over fifty different laboratories, striving to stay in sync with the Atomic second (SI) and not the rotation of the earth. UTC is calculated from TAI, as are many other time standards of today. The main difference between UTC and TAI is that occasionally, UTC has a leap second added on to it when it’s deemed appropriate by the International Earth Rotation Service. Time standards will continue to evolve as our technology evolves and keeps pace with man’s seemingly unquenchable desire for more accurate timekeeping. Just as calendars and clocks continue to become more accurate, so to do the standards by which such devices are set – the current atomic time is merely the next step in a long series of strides toward a perfected system of global time measurement. Measuring time - Exceptions to time measurementNo system is perfect. It has taken astrologers, scientists, and mathematicians alike, centuries to construct the calendars and clocks we revolve our lives around to today. Even after centuries of hard work and continual modifications, there are still flaws in our time keeping processes that occasionally arise and need to be dealt with. No sooner does a problem pop up however, than someone comes up with a mechanism to remedy it.The earth does not orbit the sun in an exact number of days. After three-hundred-sixty-five days, the earth is one fourth of a day behind the original point it was at three-hundred-sixty-five days earlier. Therefore, after four years, the earth is a full day behind where the calendars say it should be. Leap years are thus implemented as a catch up tool. Once every four years, an extra day is added to the month of February to accommodate this missing day. We now measure precise time using atomic clocks. The earth’s rotation however, is constantly slowing down due to the breaking action of the tides. Since the earth is slowing down relative to atomic clock time, we lose a fraction of an atomic clock second each time the earth rotates on its axis. To compensate for this loss and keep the atomic clocks synchronized with the earth’s rotation, a leap second is sometimes inserted (usually on New Year’s Eve). The first leap second was added in 1972 and 21 others have been added since then. Although it is not used in quite the same way as leap years and leap seconds, daylight saving time serves an equally influential purpose. It compensates for alterations in time caused by fluctuations in the earth’s movement. Near the equator, days and nights are approximately twelve hours each. The further north or south one travels from the equator however, the more that daytime hours extend significantly during that hemisphere’s summer months. By moving the clocks forward an hour it gets darker later, thereby allowing people to take advantage of the larger amount of light in the evenings. Surveys conducted by the US Department of Transportation as well as polls taken of the population in New South Wales, Australia indicate that this feeling of maximum daytime is the reason that most people have no qualms with daylight saving –or, as it is commonly, though inaccurately known, “daylight savings” (webexhibits). Daylight Saving time serves a dual purpose as well by cutting down on the amount of electricity needed for lighting, and thus decreasing the overall energy consumption anywhere from 1% to 5% nationwide. In addition to recreational and electrical benefits, it has been noted that the extra daylight decreases the number of car crashes in the evenings. Opponents of daylight saving time however will be quick to point out that the number of automobile related incidents and their severity increases in the darker mornings, resulting in more fatalities. Even safe drivers will undoubtedly be affected by the needed shift in sleep schedules, which poses an even greater problem for those with sleeping disorders. Arguments have also been made against the claim of energy conservation, saying that people use more gasoline during the extra daylight traveling around. Some “ultra-Orthodox Sephardic Jews [in Israel] have campaigned against DST because they recite Slikhot penitential prayers in the early morning hours during the Jewish month of Elul (webexhibits). The idea of daylight saving time originated with Benjamin Franklin. It was introduced to the British House of Commons in 1909 but was not instituted until World War Two. From 1966 until 2005, the DST took place from 2:00AM on the first Sunday in April until 2:00AM on the last Sunday of October. In 2005 however, George W. Bush signed the Energy Policy Act, pushing the dates for DST back to March and forward to November, beginning in 2007. There are many parts of the world that don’t practice daylight saving time, including some U.S. states such as Hawaii and Arizona and some U.S. territories such as Puerto Rico, the Virgin Islands, and Guam. Japan and India are at the top of the list of countries that don’t have any DST at all. In addition, the countries in the tropics have no need for it, and China stopped observing it in 1991. |
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