Time zone

“ All over the Solar System, except on Earth itself, the clocks read the same as they do in Greenwich, England. Time zones don't mean anything anywhere except on Earth, where the natives feel that the sun should be at the zenith when the clock says twelve. ”

“ Ten countries (Australia, Brazil, Canada, Indonesia, Kazakhstan, Mexico, New Zealand, Russia, Spain, and the United States) and the island of Greenland observe more than one official time depending on the number of designated time zones within their boundaries. An illustration of time zones throughout the world and within countries can be seen in the Standard Time Zones of the World map included in the Reference Maps section of The World Factbook. ”

“ A civil, or legal, day ends at the instant of 24 o'clock, midnight, and the next day commences. The time is continuous, the last instant of a day touching the first instant of the next. This is true for all parts of the earth; but something in addition to this happens at a certain meridian called the “date line.” Refer again to Fig. 47 which is drawn with 24 meridians representing hours. As we are taking Greenwich for our time, the meridians are numbered from 0°, on which the observatory of Greenwich stands. ”

“ Every degree by meridians is equal to four minutes of clock-time. Multiply the longitude by four, and the result in minutes is the difference of time between Greenwich and Aden, 180 minutes, or three hours. When it is noon at Greenwich, it is three o'clock at Aden, as you see in the diagram before you."
"Three o'clock in the morning, Mr. Scott?" queried the commander.
"In the afternoon, I should have added. Going east the time is faster, and vice versa," continued the young officer. ”

“ It is proposed that places located between the meridians given in the column headed “Boundaries of Sections,” shall adopt the time named in the same line in the next right hand column headed “Name of Time;” for example, places located between the meridians 671⁄2 and 821⁄2 west will adopt “Eastern” time, which is the local time of the 75th meridian, and is five hours slower than Greenwich and eight minutes 12.09 seconds faster than Washington time. ”

“ Some Chinese and Japanese methods of dividing the day and night are indicated in Fig. 1. The old Japanese method divides the day into six hours and the night also into six, each hour averaging twice as long as ours. In some cases they did this by changing the rate of the clock, and in others by letting the clock run uniformly and changing the hour marks on the dial, but this will come later when we reach Japanese clocks.
It is remarkable that at the present time in England the “saving daylight” agitation is virtually an attempt to go back to this discarded system. ”

“ Horology, as of old, is one of the exact sciences; but we find upon every street, electrically-driven clocks telling to the tenth of a second the time of day or night; the twenty-four hour system having come into general use about 1900, and London time being kept in every city in the civilized world. ”

“ You cannot manufacture a clock which will run that way because the hours of a clock must be all of exactly the same length and it must make noon at precisely 12 o'clock every day. Hence we distinguish clock time from sun time by calling clock time, mean (or average) time and sun time, apparent or solar time. From this explanation you are ready to understand such expressions as Local Mean Time, which, in untechnical language, signifies clock time at the place where you are; Greenwich Mean Time which signifies clock time at Greenwich ”

“ Therefore, we see, it might become a ticklish point in what year a man died, solely on account of this question of longitude, irrespective of any wrong-going or wrong-doing of clocks, or of any other doubtful points whatever. Sooner or later this question will have to be attended to. In all our chief towns, nearly all our towns indeed, the railway-station clocks mark Greenwich time, or, as it is called, "railway time;" the church clocks generally mark local time ”

“ We must commence with the known data that the earth revolves on its axis in twenty-four hours, or, to be more exact, in 23 hours 56 minutes 4 seconds. Astronomical clocks recording with scientific exactitude this phenomenon are on a plane apart, as are chronometers used by mariners. The astronomer uses a clock with numbers on its dial plate up to twenty-four; the common clock has only twelve hour numerals.
To come straight to modernity, it must be recognized that the measurement of time scientifically and the measurement of time according to civil law are two different things. ”

“ It will be clear to the reader, by this time, that the great point in determining the longitude is, to have the true time of Greenwich or some other reference station, in order that, by comparing this time with ship-time, the longitude east or west of the reference station may be ascertained. Ship-time can always be determined by a morning or afternoon observation of the sun, or by observing a known star when toward the east or west, at which time the diurnal motion raises or depresses it most rapidly. ”

“ When it reaches its greatest height over a western city it has, therefore, already passed its greatest height over an eastern one. In other words, when it is noon, or twelve o'clock, in the western city, it is already after noon in the eastern city. This is the simple and evident cause of time differences in different parts of the country. Of any two places the eastern one always has later time than the western. ”

“ The astronomer’s clock, for instance, is no standard of the efflux of time; it serves but to subdivide, with approximate accuracy, the interval of successive passages of a star across the meridian, which it may effect perhaps to the tenth part of a second, or 1/864000 part of the whole. The moving globe itself is the real standard clock, and the transit instrument the finger of the clock, while the stars are the hour, minute, and second marks, none the less accurate because they are disposed at unequal intervals. ”

“ As we move westward our day commences later and later than theirs, as shown above. Suppose we arrive at the eastern edge of the 180° line on Saturday at 12 o'clock, but before we cross it we call over to the islanders,—what day is it? We would get answer, “Sunday;” because all our days have been longer, totalling one day in the circuit of the globe. So if we step over the line at 12 o clock Saturday, presto, it is 12 o'clock Sunday. It looks like throwing out 24 hours, but this is not so, since we have lived exactly the same number of hours and seconds as the islanders. ”

“ To discover, therefore, whether our clock is right on any given night, it is merely necessary to watch a star with the telescope, and note the exact instant by the clock when it reaches the little cross in the field of view. Knowing from the astronomical tables the time when the star ought to have been on the meridian, and having observed the clock time when it is actually there, the difference is, of course, the error of the clock. ”

“ It is a simple thing to ascertain the true time of day by an observation of the sun, which marks the hours in his track; and when we get our observation, we have some one to note the time at a particular instant on the chronometer. By noting the hour, minutes, and seconds, at Greenwich, at the very instant we observe here, when we have calculated from that observation the time here, we have only to add, or subtract, the time here from that of Greenwich, to know precisely how far east or west we are from Greenwich, which gives us our longitude. ”

“ Hours, minutes, and seconds are aliquot parts of this unit convenient for use in dealing with shorter periods than a day, and the week, month, and year which we use in our calendars are multiples of the day.
Strictly speaking, a day is not the time required by the earth to make one revolution upon its axis, but it is best defined as the amount of time required for a particular part of the sky to make the complete circuit from the meridian of a particular place through west and east back to the meridian again. ”

“ It is well that modern clocks have no wise saws and [Pg 32] mottoes telling of the unalterable hand of Time; "Old Time, the clock-setter, that bald sexton, Time," as Shakespeare says in King John.
Early Mechanism.—The problem for the old clockmakers who wished to supplant the primitive measurement of time by candle, by the hour-glass, and later by the sundial, was to produce a piece of mechanism which would in twenty-four hours, the prescribed period of day and night, indicate the flight of time hour by hour. ”

“ Now, the exact time of the day at the place where we are, can be ascertained by well known and easy observations of the Sun if visible for a few minutes at any time from his being ten degrees high until within an hour of noon, or from an hour after noon until he is only 10 degrees high in the afternoon; if therefore, at any time when such observation is made, a Timekeeper tells us at the same moment what o'clock it is at the place we sailed from, our Longitude is clearly discovered. ”

“ The time-table shews the Greenwich time when the trains should arrive at each station, and if they be regular, they serve the purpose of a clock. If a person wishes to know the longitude of the station, he has only to ascertain the local time from a sun-dial, and the difference between this and the railway time gives the longitude. What the railway train is to the landsman, the moon is to the mariner, and while the landsman uses a dial to ascertain the local time, the sailor uses a sextant. ”

“ The right ascension of the meridian is the same thing, exactly, as the hour angle of the First Point of Aries, and both of these are identical with the local sidereal time. The sidereal time of Greenwich mean noon is the same as the right ascension of the mean sun at that time. The hour angle of a star plus the right ascension of the same star is equal to the local sidereal time. ”

“ The astronomical clock is the constant companion of the transit instrument. This clock is so regulated as to keep exact pace with the stars, and of course with the revolution of the earth on its axis; that is, it is regulated to sidereal time. It measures the progress of a star, indicating an hour for every fifteen degrees, and twenty-four hours for the whole period of the revolution of the star. Sidereal time commences when the vernal equinox is on the meridian, just as solar time commences when the sun is on the meridian. ”

“ Mr. de Struve, Delegate of Russia. On behalf of the Delegates of Russia, I beg to make the following remarks:
We have already expressed the opinion that the universal time could be properly used for international postal, railway, and telegraphic communications. But it is to be understood that local or any other standard time, which is intimately connected with daily life, will necessarily be used side by side with the universal time. ”

“ Even in this country, where more importance is attached to accurate time, I have found it a common practice in outlying parts of Wales (where Greenwich time is about twenty minutes fast by local time) to keep the clock half an hour fast by railway—i. e., Greenwich—time, or about fifty minutes fast by local time. And the farmers appeared to find no difficulty in adapting their hours of labor and times of meals to a clock which at certain times of the year differed more than an hour from the sun. ”

“ This is railroad time for Great Britain; but it is 20 minutes too fast for the west of England. This led to no end of confusion and clocks were often seen with two minute hands, one to local and the other to railroad time. This mixed up method was followed by “standard time,” with which we are all pretty well acquainted. Simply, standard time consists in a uniform time for each 15° of longitude, but this is theoretical to the extreme, and is not even approached in practice. ”

“ A good clock is also a necessary adjunct for astronomical observations, and the astronomical clocks and chronometers now in use record the time with almost perfect accuracy. The improvement in telescopes, the use of micrometers, etc., have greatly facilitated observations. In the transit clock we have a most useful timekeeper, for the ordinary clocks are not sufficiently accurate for very close observations. The sidereal time differs from solar time, and the twenty-four hours’ period is calculated from the moment a star passes the meridian until it passes it again. ”

“ It is useless multiplying examples; all difficulties disappear, as if by magic, the moment we can free our minds of local time and the association of the same hour with the same portion of the day at all places. The great interest at present manifested in the attempts to reach the North Pole calls for some consideration of universal time in the extreme north. Commencing at the equator, it is easy to see that the day and night ring, Fig. 46, would represent the days and nights of 12 hours at all seasons. ”

“ A 'day' in our ordinary use of the term is somewhat longer than this; it is the average time from one noon to the next, and as the earth whilst turning round on its axis is also travelling round the sun, it has to rather more than complete a rotation in order to bring the sun again on to the same meridian. ”

“ The sun-dial time is used on our chart as it more universally applies at different meridians on a given latitude, than does our standard time which, for the sake of timepiece uniformity, is a compromise based on mean solar time. As the earth’s orbit is such as to make the sun gain a little or lose a little in crossing the meridian each day during the year, the total annual time of the sun is averaged into uniform daily periods, which in turn are divided into 24 uniform hours and referred to certain meridians the world round, about an hour apart. ”