CALANDARS AND SUNDIALS:

1. CALANDARS AND SUNDIALS:

2. Astronomical basis of calendars The principal astronomical cycles are the day (based on the rotation of the Earth on its axis), the year (based on the revolution of the Earth around the Sun), and the month (based on the revolution of the Moon around the Earth).

3. Calendars A calendar is a system of organizing units of time for the purpose of reckoning time over extended periods. By convention, the day is the smallest unit of time in a calendar. The common theme of calendar making is the desire to organize units of time to satisfy the needs and preoccupations of society.

4. Calendars have provided the basis for planning agricultural, hunting, migration cycles, and for maintaining cycles of religious and civil events. Whatever their scientific sophistication, calendars have developed as social contracts, not as scientific discoveries. However, calendars serve as a link between mankind and the cosmos.

5. According to a recent estimate (Fraser, 1987), there are about forty calendars used in the world today.

6. The principal astronomical cycles are the day (based on the rotation of the Earth on its axis), the year (based on the revolution of the Earth around the Sun), and the month (based on the revolution of the Moon around the Earth). The complexity of calendars arises because these cycles of revolution do not comprise an integral number of days, and because astronomical cycles are neither constant nor perfectly compatible with each other.

7. For Instance, we have; • Solar Day – The time from one noon to the next. In doing so • the earth must rotate one degree more than 3600 • for the sun to get back to the same apparent • position. This results in a time difference of • 3.9 minutes longer than a sidereal day. • b. Sidereal Day – The time needed between successive risings • of a given star. A true 3600 rotation. The difference is created because the Earth rotates around the sun as it revolves on its axis. The difference in position is one degree of rotation to get to the same position.

8. Sidereal Month – Time required for the moon to complete one • cycle around the celestial sphere in respect • to it’s position with the stars. (27.3 days) • b. Synodic Month – Time required for the moon to complete a • full cycle of phases. (29.5 days) Because of the Earth’s motion around the sun, the moon must complete slightly more than one full revolution To return to the same phase in its orbit.

9. Sidereal Year – The time required for the constellations to • complete one cycle of the celestial sphere • so that the constellations return to their • original position. (365.256 mean solar days) • (about 20 minutes longer) • b. Tropical Year – The time from vernal equinox to the next • (365.242 mean solar days) This difference is due to the precession of the earth on its axis

10. Calendar Reform In most societies a calendar reform is an extraordinary event. Adoption of a calendar depends on the forcefulness with which it is introduced and on the willingness of society to accept it. For example, the acceptance of the Gregorian calendar as a worldwide standard spanned more than three centuries

11. The legal code of the United States does not specify an official national calendar. Use of the Gregorian calendar in the United States stems from an Act of Parliament of the United Kingdom in 1751, which specified use of the Gregorian calendar in England and its colonies. However, its adoption in the United Kingdom and other countries was fraught with confusion, controversy, and even violence (Bates, 1952; Gingerich, 1983; Hoskin, 1983). It also had a deeper cultural impact through the disruption of traditional festivals and calendrical practices (MacNeill, 1982).

12. In a solar calendar, the year begins at approximately the same place in the cycle of seasons. To ensure this, the number of days in the year must vary from year to year. This can be done by having common years of 365 days and leap years of 366 days. • Gregorian calendar • Julian calendar • C. Coptic calendar • D. Thai solar calendar

13. The Gregorian calendar is the calendar currently used in the Western world. It is a modification of the Julian calendar, was first proposed by Neapolitan doctor Aloysius Lilius, and adopted by Pope Gregory XIII on February 24, 1582 (the document was dated 1581 on account of the pope starting the year in March). The mean year in the Julian Calendar was a little too long so causing the Vernal equinox to drift earlier in the calendar year. This was why the Gregorian calendar was invented

14. The Julian calendar was introduced by Julius Caesar in 46 BC, taking force in 45 BC or 709 ab urbe condita. It was chosen after consultation with Sosigenes and was obviously designed to approximate the tropical year as it was known at the time. It has a regular year of 365 days divided into 12 months, and a leap day is added every 4 years. The calendar remained in use into the 20th century in some places. However with this scheme too many leap days are added with respect to the astronomical seasons, which on average occur earlier in the calendar by about 11min per year. It is said that Caesar was aware of the discrepancy, but felt it was of little importance

15. The Coptic calendar is used by the Coptic Orthodox Church. It divides the year into 13 months: 12 months of 30 days each plus an intercalary month of either five or six days, depending on whether the year is a leap year. The Coptic year begins on the Feast of Neyrouz, the first day of the month called Tout, which is equivalent to September 11 in the Gregorian calendar, except before a Gregorian leap year when it's September 12.

16. The Thai solar, or Suriyakati, calendar is used in traditional and official contexts in Thailand, although the Western calendar is used for business. The months and days of the week are the same as those used in the Western calendar, only their names differ. The year however is counted from the Buddhist Era (B.E.), which is 543 years earlier than the Christian era (A.D.). For example, 2003 A.D. is equivalent to 2546 B.E. The era is based on the death of Gautama Buddha, which is dated to 543 BC by the Thai.

17. The Islamic calendar is the most well known calendar that is not a solar calendar. Its year of 12 lunar months drifts slowly through the seasons. It is a lunar calendar. The Islamiccalendar is a purely lunar calendar of 12 months and a lunar year of usually 354 days. Each month can be either 29 or 30 days long. Because the lunar year is shorter than the solar year, Muslim holy days cycle backwards in relation to the purely solar Western calendar. This had given rise to a Western misperception. The Islamic lunar calendar is not inaccurate, because it is a pure lunar calendar.

18. The following have lunar months and are thus lunisolar calendars: Hebrew calendar Chinese calendar Thai lunar calendar

19. The Hebrew calendar is the annual calendar used in Judaism. It is based upon both the lunar cycle (which defines months) and the solar cycle (which defines years). This is in contrast to the Gregorian calendar, which is based solely upon the solar cycle, or the Islamic calendar, which is purely lunar.

20. The Chinese calendar is a lunisolar calendar formed by combining a purely lunar calendar with a solar calendar. Among Chinese, the calendar is not used for most day to day activities, but is used for the dating of holidays such as Chinese New Year (Spring Festival) and the Mid-Autumn Festival and for divination. The primary use in day to day activities is for determining the phase of the moon, which is important for farmers and is possible because each day in the calendar corresponds to a particular phase of the month.

21. The Thai lunar, or Chantarakati, calendar was used in Thailand until 1888, when it was replaced by the Thai solar calendar which is used today. The Buddhist feasts are still fixed according to the Chantarakati, which make them move their date in the solar calendar

22. History of the Sundial "In today's complex digital world, the sundial has become a forgotten timepiece. While not as convenient as a wristwatch, a sundial links timekeeping to its ancient celestial origins, and a well-designed one can accurately tell time to the minute." (Mayall, 1994)

23. The sundial dates back to the Egyptian Period, around 1500 B.C. It was also used in ancient Greece and Rome. In central Europe it was the most commonly used method to determine the time, even after the mechanical clock was developed in the 14th century. The sundial was actually used to check and adjust the time on mechanical clocks until late into the 19th century

24. The Armillary Type Sundial Armillary or ring sundials consist of a system of rings that represent the major circles of the terrestrial and celestial spheres. The hour lines are evenly spaced on the equatorial ring. The style is the axis of the sphere

25. Conical or Scaphe dials The conical, scaphe or bowl sundial uses the concave segment of a circular cone as the dial face. They are similar in appearance to the hemicyclium, which was invented by the Greeks and then copied by the Romans.

26. Cylindrical or pole sundials Portable cylinder or pillar sundials are also called poke dials or shepherd's dials, because they used to be carried in the pockets (pokes) by shepherds. Another name for this dial is the traveler's dial. The dial is in the form of a cylinder with the gnomon attached to a movable top. The hour lines are in the form of curves inscribed or printed on the cylinder. To tell the time, the gnomon is set over the vertical line of the day and the time read off where shadow of the point of the gnomon falls on a hour line.

27. Digital sundials The digital sundial is a fairly recent invention. The time is displayed in digits or even in words or pictures. This sort of dial is not easy to built and works as follows: "Two closely-spaced parallel masks project different images depending on the angular position of the sun in the following way: The first mask casts a striped light pattern which is dependent on the height of the sun onto the second mask The second mask is composed of narrow stripes of the digits to be displayed.The striped pattern of sunlight cast by the first mask illuminates exactly those stripes of the second mask corresponding to the image representing the current time." (Scharstein, 1996.)

28. Equatorial or universal dials The equatorial or universal sundial is the easiest dial to make. The gnomon is parallel to the earth's axis and the dial plate lies in the plane of the equator. The hour lines are spaced at 15°, so that the face looks very much like that of a traditional clock. The equatorial sundial has one limitation though; it does not work when the sun is on the celestial equator, i.e. during the equinoxes, because the sun's light falls on the edge of the dial plate.

29. Horizontal dials This type of sundial is commonly found in gardens on a pedestal. The dial plate of the horizontal sundial is of course horizontal. The gnomon or style makes an angle equal to the latitude of the place it was designed for. Horizontal dials are directional dials.

30. Sundials as Jewelry Portable sundials are also made up as jewelry. Although their main function in this case is mostly decorative, some of them are amazingly accurate. To read the time on this pendant, the string is placed in line with the month. Then the pin is inserted from behind and the time is read on the outer scale in the morning and on the inner scale in the afternoon

31. Reflected ceiling dials Reflected ceiling dials are not common. A mirror is laid horizontally on a north-facing window sill - if you live in the southern hemisphere - or on a pole outside of the window. The hour lines are drawn on the ceiling. They will have the shape of a slightly distorted 8. The sun spot will tell you not only the time, but also the date.

32. Ring dials The ring dial makes use of light, not a shadow to indicate the time. Sunlight falls through a tiny hole onto the hour lines marked on the inside of a ring. The ring has to be turned so that the light spot falls on the correct date line.Traditionally ring dials were very small, less than 25 mm in diameter; this made them difficult to read. There is no reason against making them bigger. The one in the photo has a diameter of 10 cm. Ring dials are altitude dials.

33. Vertical dials After the horizontal sundial the vertical sundial is probably the most common. Its biggest advantage is that it is visible from a distance.In Europe vertical dials can be found on East, West and South facing walls. Of course those on East and West facing walls only tell the time for part of the day. This beautiful vertical dial is in Groningen, the Netherlands.

34. The Polar Sundial The dial plate of a polar sundial is parallel with the earth's axis. The gnomon (style) is parallel to the dial plate and the hour lines are parallel to the gnomon and to each other. The distance between the hour lines is not dependent on the latitude but only on the height of the style. This dial is seldom seen and is normally used in combination with other dials

35. How to make your own Sundial