Do we take the calendar for granted or are we totally dependent on it? Over the past few weeks several calendar related questions were asked of me. In the last blog article I stated that the reckoning or changing of the date of the year varied by time and place. Someone
asked me to elaborate. Since the holiday of Pesah is coming and Nisan is the first of the months, someone asked me why is Nisan the first month and Rosh Hashana at the beginning of the seventh month. Another person pointed out that some units of time are natural (i.e based on astronomically observed events) and some are human convention. The calendar is designed for societal needs. There many kinds of calendars. Some list only holidays or events and others list every day of the year. As long as the calendar meets societal needs and it is consistent in the following of its own rules, it is accurate. This article attempts to seek out the common basis to answer all these questions.
A full calendar is marker for time that we use to keep track of the days of the week, the days of a month, the months and the year, but did you ever consider that some measures for time are natural and some totally artificial? A day is the rotation of the earth on its axis. A month is the time the moon rotates around the earth and a year is the rotation of the earth around the sun.
How did an hour become 1/24 of day and an hour divide into 60 minutes and a minute into 60 seconds? Hours, minutes and seconds are human conveniences. In today’s number systems we use base 10 which is commonly thought to correspond to ten fingers. In other systems such as ancient Babylonia and Sumar, they used base 12 or 60. Twelve is the number of digits (also called phalanges) on our fingers when not including the thumb. The thumb could have been used to count the digits. Hence 24 is both hands and 60 is five fingers times the 12 digits on the other hand. This is speculation as we have no documentary evidence.
The first clocks were sticks placed in the ground to act as a sundial. A refinement was to add marks to measure and calibrate movement of the sun. The time between sunrise and sunset was divided into 12 parts. In the ancient Jewish time calculations this was a halachic (legal) hour. Twelve parts or hours are either from the base 12 finger counting system or from the twelve yearly cycles of the moon.
This was the same way that the ancient Greeks and Romans divided the day. Noon, when the sun is at its greatest height in the sky is halfway between sunrise and sundown. The length of the hour varied with the season. In the Middle East the number of daylight hours varies less than in Chicago. For example the range from the most hours of daylight to the least in Chicago is about 6:05 hours and in Jerusalem it is 4:09 hours.
The exact measurement of time was important for religious rituals. The ancient priests in the Middle East had rituals that were time dependent. For example the very first chapter in the Talmud, Berakhot discusses the correct time for reciting the prayer, Shema and the morning prayers. Ancient Egypt and Babylonia also had time dependent rituals.
Sun dials were fine when the sun shined. At night people needed to use marked candles, oil lamps, or dripping water clocks. People needed to know time more precisely than in hours.
What is week? There is no natural reason that a week is seven days. The 354 days of a lunar 12 month cycle and the 365  days of the solar year are not evenly divisible by 7. One theory is that 360 is close to the number of days in a year. 360 is evenly divisible by three and six (i.e. no fractions or remainders) unlike 10 or 100. The Bible gives us six days of creation and the seventh day of the week is the Sabbath, the day of rest. That is our week.
What is the first day of the year?
There is no straight forward answer. The first chapter in Talmud Rosh Hashana discusses the four new years, Nisan for the liturgical year i.e cycle of holidays; Tishrei for counting of years and sabbatical years, Elul for animals; and Shevat for trees. I am only concerned with the first two. The Torah tells us that Rosh HaShanah of Tishei is the seventh month and Nisan is the first of months. We change the year of calendar on the first of Tishrei. The counting of Pesah as the first holiday of the year really makes very little difference in keeping track of time or dates. The interesting question is why January 1 is the beginning of the year. Tishrei is connected to fall and Nisan with spring. In the solar/secular calendar fall is a natural beginning because the summer harvests are over. We start our school year in the fall. Spring is natural for a new year because the plants that were dormant over the winter start to grow.
Without getting into a prolonged discussion, the winter solstice is associated with the constellation Capricorn. In astrology this period is December 22 to January 19. Capricorn is ruled by the planet named for the Roman god, Saturn. Ancient Rome had a holiday, Saturnalia. This was a festival of lights. Originally the date was December 17, but because of the Julian calendar corrections, the day became December 25 . Seven days later is January 1, which is Kalenda.
In Talmud Avodah Zara 8a is a description a pagan festival called Saturna which occurs eight days before the winter solstice. It is followed eight days after the solstice with a festival called Kalenda. The Talmud ascribes the origins of this festival to Adam, who saw that the days were getting shorter and thought it was punishment for his sin. He was afraid that the world was returning to the chaos and emptiness that existed before creation. He sat and fasted for eight days. Once he saw that the days were getting longer again he realized that this was the natural cycle of the world, so made eight days of celebration. The Talmud states that this festival was later turned into a pagan festival.
The darkness gave Adam what we call winter depression. Adam did not know the cycle of the year is to have days that get shorter and after winter solstice they get longer. Saturnalia became a festival of lights to conquer the darkness. Note the connection to lights on the Christmas tree and the lights on the menorah. The lights of Hanukkah increase each night to match the increasing length of daylight. The winter solstice can not be assigned an exact Hebrew date that will work every year. However, since Pesah always falls in the spring, we can count the days until Kislev, making Kislev correspond to the beginning of winter. In the cycle of the lunar months, the 14th or 15th of the month is a full moon, the day with most moonlight. The last week of the month is the darkest as the time is before the new moon. The new moon is the first day the moon is visible. Hence, Kishlev 25 is a good choice. A celebration  on that begins on Kishlev 25 that lasts eight days will include the new moon or rosh hodesh Tevet.
In the Roman calendar, Kalenda (Kalendae), would make a good choice for the new year because it was the 8th day after the start of the winter solstice holiday. Just as the days stop getting shorter, there is a holiday to celebrate the new year of longer daylight. Saturnalia and Kalenda were legal holidays in Roman times when no business was conducted. Perhaps this is an explanation for a “natural” reason for a January 1 new year?
We already have a fall and a spring new year date; why should the winter date be any more reasonable? The information on the Ancient Roman calendar is limited. We do know that the year had 10 named months. That is why September means seventh month and December means 10th month. Bernard Allen , referring to O. E. Hartmann,  suggests that the 10 month year corresponds the ten month vegetation year and is analogous to our 9 or 10 month school year. The 60 days for the months of winter i.e. January and February were not numbered. Hartmann speculated that farmers did not do much in the winter months. That would indicate that March 1st  is a “natural” choice for the first day of the year and that was the date for new year in pre-Caesarian Rome.
Janus was the two faced Roman god of change and new beginnings; one face for the future and one for the past. January was named for Janus and the first day was a celebration. January 1st was the 8th day after December 25th. January 1st was the date the Roman consuls began serving their term. In the Catholic liturgical calendar January 1 was the Feast of the Circumcision of Jesus, but this is confusing two time periods. Europeans celebrated the new year on December 25, March 1, March 25, and Easter.
In medieval Europe, however, the celebrations accompanying the new year were considered pagan and unchristian like, and in the year 567 the Council of Tours abolished January 1 as the beginning of the year and forbade celebrations. At various times and in various places throughout medieval Christian Europe, the new year was celebrated on Dec. 25, the birth of Jesus; March 1; March 25, the Feast of the Annunciation  ; and Easter.
H. J. Rose  suggests that what we know about the calendar before Julius Caesar is speculation. The early Roman calendar, unlike the Jewish calendar, was not connected to the seasons. The early Romans did not seem to care. Since the 10 month year of either 295 or 304 days depending on how you counted was not even close to the solar year, November was not always in the fall. Eventually to correct this, an extra month was added about three times in eight years to keep the numbered months in the correct season. Few Roman days had special names. The Jewish calendar has named holidays associated with a particular day of a particular month. However, in the Torah the months don’t have names.
The calendar that Julius Caesar enacted with names for the months and fixed numbers of days per month is pretty close to our current calendar. This is the Julian calendar. This calendar modified by Pope Gregory in 1582 with the addition of ten days to correct the shift of dates and realign the solar year to the date on the calendar. By 1582 the vernal equinox was March 11 not March 21. The vernal equinox sets the date of Easter. The Gregorian calendar was immediately adopted in Catholic countries. In other countries acceptance was slowed by political or religious reasons. Russia only accepted it 1918 after the revolution. Greece was the last European country to accept it in 1923. 
Perhaps you are wondering how 16th century scientists knew the exact date of the equinox, solstice or length of the year? After all Galileo Galilei first pointed a telescope to the sky in 1609. 16th century observations used a room sized camera obscura. The room was a darkened church and the pinhole in the roof made a lens that focused the sun’s image on the wall. The wall had a map with a metal line that charted the movement of sun at precisely noon. The extremes of the line made by the sun were the winter
and summer solstices.
The calendar was created for the convenience of society. In an agricultural society, people needed to keep track of seasons. Agricultural holidays commemorated the change of seasons. When society needed times for religious ritual a system of time was invented based on solar observations. For example the times for morning prayers and the times to start and end the Shabbat and holidays needed to be predictable. Since the length of a day and month are not evenly divisible into the length of a year, some compensation needed to be made to keep seasonal festivals in their proper season. The adjustment is a leap month, leap day or leap second.
Each of the dates for the new year, fall, winter and spring are based on the movement of the earth around the sun. Since the new year automatically starts at the moment the old year ends, this article while it ends here, never will be completed.
Postscript for April 1
The origin for April 1 as "April Fool's" is not certain. In today's Time Magazine Daily Brief is an article by Jennifer Latson (http://time.com/3757913/history-april-fools-day/) suggesting that it started in 1582 after France adapted the Gregorian calendar. In many places new year was celebrated on March 25. If there was an eight day celebration, it would end on April 1. Those who celebrated New Year on January 1 called the March 25thers fools. This theory is suspect since Chaucer mentions a new year in the Nun's Wife's Tale http://sites.fas.harvard.edu/~chaucer/teachslf/npt-par.htm#TALE
Whan that the month in which the world bigan,
When the month in which the world began,
That highte March, whan God first maked man,
Which is called March, when God first made man,
Syn March [was gon], thritty dayes and two,
Since March had gone, thirty days and two
Thirty-two days after March 1 is April 1.
 The Jewish year could have 354, 355, or 356 days depending on how many 29 and 30 day months.
 For a fuller discussion on Saturnalia see: “Saturnalia” in Wikipedia http://en.wikipedia.org/wiki/Saturnalia. The holiday’s customs changed over the years.
 December 25 was a pagan holiday long before it became a Christian one.
 See Menachem Leibtag’s article, “Chanuka - its Biblical roots - Part Two”
http://www.tanach.org/special/chanuka2.txt where he discusses this Midrash. The Talmud describes observances of the Roman holidays of Saturnia and Kolenda that are very close to the Romans sources described in the above Wikipedia article. The legend also appears in Ginzberg, Louis. Legends of the Jews, (Philadelphia; Jewish Publication Society, ©1937) v. 1 page 89.
 Also spelled Calenda and it is the root for the English “calendar” and German “Kalendar.”