Astronomical Myths: Based on Flammarions's "History of the Heavens"

by J. F. Blake; Camille Flammarion

It was in the year 1582 that the Gregorian reform was put into operation. At that epoch the vernal equinox happened on the 11th instead of the 21st of March. To get rid of this advance of ten days that the equinox had made and to bring it back to the original date, Pope Gregory decided that the day after the 4th of October, 1582, should be called the 15th instead of the 5th. This change only did away with the inconvenience at the time attaching to the Julian calendar; it was necessary to make also some modification in the rule which served to determine the lengths of the civil years, in order to avoid the same error for the future.

So the Pope determined that in each 400 years there should be only 97 bissextile years, instead of 100, as there used to be in the Julian calendar. This made three days taken off the 400 years, and in consequence the mean value of the civil year is reduced to 365·2425 days, which is not far from the true tropical year. The Gregorian year thus obtained is still too great by ·000226 of a day; the date of the vernal equinox will still then advance in virtue of this excess, but it is easy to see that the Gregorian reform will suffice for a great number of centuries.

The method in which it is carried out is as follows:—In the Julian calendar each year that divided by four when expressed in its usual way, by A.D., was a leap year, and therefore each year that completed a century was such, as 1300, 1400 and so on—but in the Gregorian reform, all these century numbers are to be reckoned common years, unless the number without the two cyphers divides by four; thus 1,900 will be a common year and 2,000 a leap year. It is easy to see that this will leave out three leap years in every 400 years.

The Gregorian calendar was immediately adopted in France and Germany, and a little later in England. Now it is in operation in all the Christian countries of Europe, except Russia, where the Julian calendar is still followed. It follows that Russian dates do not agree with ours. In 1582, the difference was ten days, and this difference remained the same till the end of the seventeenth century, when the year 1700 was bissextile in the Julian, but not in the Gregorian calendar, so the difference increased to eleven days, and now in the same way is twelve days.

Next to the year, comes the day as the most natural division of time in connection with the earth, though it admits of less difference in its arrangements, as we cannot be mistaken as to its length. It is the natural standard too of our division of time into shorter intervals such as hours, minutes, and seconds. By the word day we mean of course the interval during which the earth makes a complete revolution round itself, while daytime may be used to express the portion of it during which our portion of the earth is towards the sun. The Greeks to avoid ambiguity used the word nyctemere, meaning night and day.

No ancient nation is known that did not divide the day into twenty-four hours, when they divided it at all into such small parts, which seems to show that such a division was comparatively a late institution, and was derived from the invention of a single nation. It would necessarily depend on the possibility of reckoning shorter periods of time than the natural one of the day. In the earliest ages, and even afterwards, the position of the sun in the heavens by day, and the position of the constellations by night, gave approximately the time. Instead of asking What "o'clock" is it? the Greeks would say, "What star is passing?" The next method of determining time depended on the uniform motion of water from a cistern. It was invented by the Egyptians, and was called a clepsydra, and was in use among the Babylonians, the Greeks, and the Romans. The more accurate measurement of time by means of clocks was not introduced till about 140 B.C., when Trimalcion had one in his dining chamber. The use of them, however, had been so lost that in 760 A.D. they were considered quite novelties. The clocks, of course, have to be regulated by the sun, an operation which has been the employment of astronomers, among other things, for centuries. Each locality had its own time according to the moment when the sun passed the meridian of the place, a moment which was determined by observation.

Before the introduction of the hour, the day and night appear to have been divided into watches. Among the Babylonians the night was reckoned from what we call 6 A.M. to 6 P.M., and divided into three watches of four hours each—called the "evening," "middle," and "morning" watch. These were later superseded by the more accurate hour, or rather "double hour" or casbri, each of which was divided into sixty minutes and sixty seconds, and the change taking place not earlier than 2,000 B.C. Whether the Babylonians (or Accadians) were the inventors of the hour it is difficult to say, though they almost certainly were of other divisions of time. It is remarkable that in the ancient Jewish Scriptures we find no mention of any such division until the date at which the prophecy of Daniel was written, that is, until the Jews had come in contact with the Babylonians.

Some nations have counted the twenty-four hours consecutively from one to twenty-four as astronomers do now, but others and the majority have divided the whole period into two of twelve hours each.

The time of the commencement of the day has varied much with the different nations.

The Jews, the ancient Athenians, the Chinese, and several other peoples, more or less of the past, have commenced the day with the setting of the sun, a custom which perhaps originated with the determination of the commencement of the year, and therefore of the day, by the observation of some stars that were seen at sunset, a custom continued in our memory by the well-known words, "the evening and the morning were the first day."