Solar and Lunar Calendars

 

We know that the lunar month lasts about 29 1/2 days. Twelve such months amount to about 354 days.

 

This interval is almost 11 days shorter than the true solar year, which has 365 days, 5 hours, 48 minutes, and 46 seconds.

 

But a year of 13 lunar months would amount to about 383 1/2 days and would be more than 18 days longer than the solar year. The solar year, therefore, does not equal any whole number of lunar months.

 

The synodical month is one of three natural divisions of time. The other two are the rotation of the earth on its axis, or a day, and the revolution of the earth around the sun, or a year. Another astronomical month is the solar month, which is one twelfth of a solar year. The solar month is the time taken by the sun to pass through each of the 12 signs of the zodiac.

Our calendar months vary in length from 28 days to 31 days. The lengths of calendar months have no relation to astronomy. At first, the 12 months were 29 and 30 days alternately. Later, days were added to the months to make the year come out closer to a solar year-the time the earth takes to go once around the sun.

In the Gregorian calendar which we use today, each day of the month is called by its number. June 1 is the "first of June," and so on. The ancient Greeks divided the month into 3 periods of 10 days, and the French Revolutionary calendar used months of equal length divided into 3 parts of 10 days each. The fifteenth day of the month was called the fifth day of the second decade.

The Roman system was even more complicated. The Roman calendar had three fixed days in each month, the calends, the nones, and the ides. The Romans counted backward from these fixed days. They would say something would happen, for example, three days before the nones. The calends were the first day of the month. The ides were at the middle, either the 13th or 15th of the month. The nones were the ninth day before the ides, counting both days. When the soothsayer told Julius Caesar to "beware the Ides of March," he meant a definite day.

 

Year is the time the earth takes to make one complete revolution around the sun. There are two different kinds of years which are used by astronomers. The solar, equinoctial, or tropical year is the time between two passages of the sun through the March equinox. In the Northern Hemisphere, this equinox is called the vernal equinox. This year is 365 days, 5 hours, 48 minutes, and 46 seconds long. This year is used for all practical and astronomical purposes. It is the basis of our common or calendar year.

The sidereal year is made up of 365 days, 6 hours, 9 minutes, and 9.5 seconds. This is the time it takes the earth to return to the same place in its orbit, with reference to the fixed stars. The sidereal year is longer than the solar year because of the precession of the equinoxes. The sidereal year is seldom used except in the calculations of astronomers.

The calendar year is only 365 days long, and so we have to add an extra day every four years to correct the difference in time between the calendar year and the solar year. This fourth year is called leap year, and the extra day is February 29. Adding an extra day every fourth year makes the average calendar year 11 minutes, 14 seconds too long. So, the day is not added in the century years, except in those divisible by 400. The years 1700, 1800, and 1900 have had only 365 days. The year 2000 will contain 366 days.

Today, the leap second corrects for differences in the earth's rate of rotation from year to year. It is usually added to or subtracted from the last minute of the year.

The lunar year is made up of 12 lunar months. The ancient Greeks used this year. It contained 354 days.

In most Western nations, the calendar year begins on January 1. During the Middle Ages, however, most European nations considered March 25, Annunciation Day, to be the first day of the calendar year. By 1600, most of them had adopted the Gregorian calendar, which recognized January 1 as the beginning of the year.

The church calendar, which is used in the Roman Catholic and in most Protestant churches, is regulated partly by the solar and partly by the lunar year. This causes a difference between the fixed feast days, which always fall on the same day every year, and movable feasts such as Easter, whose dates vary from year to year. The fixed feast days are determined by the solar year, and the movable feast days, by the lunar year.

In the early ancient Roman calendar, the year began on March 1. Later, the Romans used January 1 as the new year. The Jewish year begins near the September equinox, which is known as the autumnal equinox in the Northern Hemisphere. The Islamic year is based on the changing of the phases of the moon and lasts 354 days. Therefore, the beginning of the Islamic year continually falls earlier in the seasons. Thirty Islamic years make up a cycle during which there are 11 leap years at irregular intervals.

 

Measuring time by the sun. Directly above every spot on the earth, an imaginary curved line called the celestial meridian passes through the sky. As the earth rotates on its axis, the sun crosses every celestial meridian once each day. When the sun crosses the celestial meridian above a particular place, the time there is noon. Twelve hours later, the time at that place is midnight. The period from one midnight to the next is called a solar day. The length of a solar day varies because of the tilt of the earth's axis, the oval shape of its orbit, and its changing speed along the orbit.

To make all solar days the same length, astronomers do not measure solar time with the apparent (real) sun. Instead, they use an imaginary mean (average) sun that moves at a steady speed around the sky. Local mean solar noon occurs when the mean sun crosses the celestial meridian above a particular place. The time between one mean solar noon and the next is always the same. Thus, all mean solar days are the same length.

Measuring time by the stars. Astronomers also measure time by the earth's rotation in relation to the stars. This time is called sidereal time. Each day, as the earth rotates on its axis, an imaginary point among the stars called the vernal equinox crosses the celestial meridian above every place on the earth. The time when this happens is sidereal noon. The time between one sidereal noon and the next is one sidereal day. A sidereal day is shorter than a mean solar day by 3 minutes 56.555 seconds.

Devices that measure time. The sundial was one of the earliest devices for measuring time. But it can work only in uncloudy daylight. Early peoples also used ropes with knots tied at regular intervals or candles marked with regularly spaced lines. When burned, such devices measured time. An hourglass or sandglass tells time by means of sand trickling through a narrow opening. A water clock, or clepsydra, measures time by allowing water to drip slowly from one marked container into another. By the 1700's, people had developed clocks and watches that told time to the minute. Modern electronic and atomic clocks can measure time with far greater accuracy.

Time zones Local and standard time. Clocks in various parts of the world do not all show the same time. Suppose they all did show the same time-3 p.m., for example. At that time, people in some countries would see the sun rise, and people in other lands would see it high in the sky. In still other countries, the sun could not be seen because 3 p.m. would occur at night. Instead, clocks in all locations show 12 o'clock at midday.

Every place on the earth that is east or west of another place has noon at a different time. The time at any particular place is called the local time. At noon local time in one town, the time might be 11 a.m. in another place west of the town or 1 p.m. in a place to the east.

If every community used a different time, travelers would be confused and many other problems would be created. To avoid all such problems, standard time zones were established. These zones were set up so there would be a difference of one hour between a place on the eastern edge of a time zone and a place on the western edge if each were on its own local time. But under the time zone system, each of these places is not on its own local time. The local time at the meridian (line) of longitude that runs through the center of the zone is used by all places within the zone. Thus, time throughout the zone is the same.

Time zones in the United States and Canada. The United States and Canada each have six standard time zones. Each zone uses a time one hour different from its neighboring zones. The hours are earlier to the west of each zone and later to the east. The Newfoundland Time Zone is not a true standard time zone because it differs from its neighboring zones by only a half hour. The boundaries between the zones are irregular so that neighboring communities can have the same time.

The United States has not always had standard time zones. Every locality once set its own time by the sun. Various railroads tried to make their schedules simpler by establishing railroad time along sections of their routes. But in 1883, there were still about 100 different railroad times. That year, all the railroads divided the United States into four standard time zones.

Each zone is centered on a meridian of longitude 15 apart. In the United States and Canada, the Eastern Time Zone is centered on the 75 west meridian, and the Central Time Zone on the 90 west meridian. The Mountain Time Zone is centered on the 105 west meridian, and the Pacific Time Zone on the 120 west meridian. The central meridians of the other U.S. and Canadian zones are 60 west for the Atlantic Time Zone, 135 west for the Alaska Time Zone, and 150 west for the Hawaii-Aleutian Time Zone. The Newfoundland Time Zone is a separate zone and has no central meridian.

Worldwide time zones were established in 1884. The meridian of longitude passing through the Greenwich Observatory in England was chosen as the starting point for the world's time zones. The Greenwich meridian is often called the prime meridian. The mean solar time at the Greenwich meridian is traditionally known as Greenwich Mean Time (GMT) or Greenwich Civil Time (GCT).

An international conference in 1884 set up 12 time zones west of Greenwich and 12 to the east. These zones divide the world into 23 full zones and two half zones. The 12th zone east and the 12th zone west are each half a zone wide. They lie next to each other and are separated by an imaginary line called the International Date Line. The line is halfway around the world from Greenwich. A traveler crossing this line while headed west, toward China, loses a day. A traveler who crosses the line while traveling eastward gains a day. A few places do not use standard time zones. For example, the polar regions have weeks of constant sunlight or darkness.

In the 1940's, experts began to realize that time based on astronomical measurements was not completely smooth, since the earth slowed down and speeded up in an irregular fashion. As a result, in 1958, the length of the second was redefined in terms of the natural vibration frequency of the cesium atom. However, the length of the year continued to be determined from astronomical observations. This time scale based on both atomic and astronomical measurements is called Universal Time Coordinated (UTC).

Scientific ideas about time Physical time. Scientists think of time as a fundamental quantity that can be measured. Other fundamental quantities include length and mass. The noted physicist Albert Einstein realized that measurements of these quantities are affected by relative motion (motion between two objects). Because of his work, time became popularly known as the fourth dimension.

Many physicists believe that the apparent nonstop, forward flow of time is not a property of the basic laws of nature. They consider it a result of the fact that the universe is expanding and becoming more disorganized. Some physicists have considered the possibility that, under certain circumstances, time might flow backward. However, experiments have not supported this idea.

Biological time. The activities of many plants and animals are timed to the cycle of day and night. These natural rhythms are called circadian rhythms. The most obvious example is the sleep cycle.

Many plants and animals are sensitive to other natural time cycles. Certain plants do not start their next step of growth until daylight each day lasts a certain time. Some sea animals time their activities to the changing tides. These creatures even seem to know such times away from their home waters.

Geological time. Geologists have found clues in the earth's crust that indicate how many billions of years ago it was formed. One of these indicators is the element uranium. Uranium changes slowly into the element lead by means of radioactive decay. By measuring the amount of lead in a sample of uranium ore, scientists can estimate when the rock was formed.

A second clue to geological time is radioactive carbon. This form of carbon is absorbed by every living plant and animal. The rate of the carbon's decay can help a geologist estimate how long ago the plant or animal died.

 

Before the invention of the clock, people watched the sun, the moon, and the stars to tell time. The daily rising of the sun provided a short unit of time, the solar day. The cycle of seasons roughly indicated a longer unit of time, the solar year. But early people did not know that the earth's revolution around the sun caused the different seasons. The changing position and shape of the moon was easier for them to observe. As a result, the early calendars used the interval between the successive full moons, called the lunar month, as an intermediate unit of time.

We now know that the lunar month lasts about 29 1/2 days. Twelve such months amount to about 354 days. This interval is almost 11 days shorter than the true solar year, which has 365 days, 5 hours, 48 minutes, and 46 seconds. But a year of 13 lunar months would amount to about 383 1/2 days and would be more than 18 days longer than the solar year. The solar year, therefore, does not equal any whole number of lunar months.

The discrepancy between whole lunar months and days in a solar year explains the confusion over calendar keeping during thousands of years. A calendar based on 12 lunar months becomes out of step with the seasons. Some people who used lunar calendars kept them roughly in step with the seasons by making some years 12 months long and other years 13 months long.

Some calendars today Most people in the Western world use the Gregorian calendar, worked out in the 1580's by Pope Gregory XIII. It has 12 months, 11 with 30 or 31 days. The other month, February, normally has 28 days. Every fourth year, called a leap year, it has 29 days. However, century years that cannot be divided evenly by 400 lose the extra day, though they are leap years. For example, February had 28 days in 1900 but 29 days in 2000.

The Christian church calendar is regulated partly by the sun and partly by the moon. Immovable feasts include Christmas and such feasts as the Nativity of the Blessed Virgin. They are based on the solar year. Such days as Ash Wednesday, Palm Sunday, and Easter are called movable feasts, because their dates vary from year to year, according to the phases of the moon.

The Hebrew calendar begins with an estimated moment of the world's creation. Hebrew tradition has placed this moment at 3,760 years and 3 months before the birth of Jesus Christ. To find a year in the Hebrew calendar, we must add 3,760 to the date in the Gregorian calendar. For example, 2000 in the Gregorian calendar is 5760 in the Hebrew calendar. But this system will not work to the exact month, because the Hebrew year begins in September or October in the Gregorian calendar. By mid-October 2000, for instance, the Hebrew year had become 5761.

The Hebrew year is based on the moon and normally consists of 12 months. The months are Tishri, Heshvan, Kislev, Tebet, Shebat, Adar, Nisan, Iyar, Sivan, Tammuz, Ab, and Elul. They are alternately 30 and 29 days long. Seven times during every 19-year period, an embolismic or extra 29-day month, called Veadar, is inserted between Adar and Nisan. At the same time, Adar is given 30 days instead of 29. These additions keep the Hebrew calendar and holidays in agreement with the seasons of the solar year.

The Chinese calendar begins at 2637 B.C., the year in which the legendary Emperor Huangdi is said to have invented it. This calendar counts years in cycles of 60. For example, the year 2000 in the Gregorian calendar is the 17th year in the 78th cycle. The years within each cycle are broken down into repeating 12-year cycles. In these cycles, each year is named after 10 Chinese constellations and 12 animals. The animals are the rat, ox, tiger, hare, dragon, snake, horse, sheep, monkey, rooster, dog, and pig. The year 2000 is the year of the dragon.

The Chinese year is based on the moon and generally consists of 12 months. Each month begins at new moon and has 29 or 30 days. A month is repeated seven times during each 19-year period, so that the calendar stays approximately in line with the seasons. The year starts at the second new moon after the beginning of winter in the Northern Hemisphere. Thus, the Chinese New Year occurs no earlier than January 21 and no later than February 20.

History

Early calendars usually represented some sort of compromise between the lunar and solar years. Some years lasted 12 months, and others lasted 13 months.

Calendar reform would simplify the present calendar. Two proposed calendars have received considerable support. In each, months and years would begin on the same day of the week every year. All months would contain the same or nearly the same number of days. The Fixed Calendar, also called The Thirteen-Month Calendar, would provide 13 months exactly four weeks long. The extra month, Sol, would come before July. A year day placed at the end of the year would belong to no week or month. Every four years, a leap-year day would be added just before July 1. The World Calendar would have 12 months of 30 or 31 days, a year day at the end of each year, and a leap-year day before July 1 every four years.

• Exactly 2520 years from the exile of Benjamin, Iceland became an independent nation.

 

•  The first tribe to be conquered by the Assyrians was Manasseh, in 745 B.C. Exactly 2520 years later America became a nation on July 4, 1776.

 

• Study the book: Abrahamic Covenant, (A study outline of the identity of God's people) By E. Raymond Capt - page 25