Transcript Chinese calendar

CALANDARS AND SUNDIALS:
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).
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.
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.
According to a recent estimate (Fraser, 1987), there are
about forty calendars used in the world today.
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.
For Instance, we have;
a. 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.
a. 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.
a. 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
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
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).
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.
A. Gregorian calendar
B. Julian calendar
C. Coptic calendar
D. Thai solar calendar
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
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
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.
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.
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 Islamic calendar 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.
The following have lunar months and are thus lunisolar calendars:
Hebrew calendar
Chinese calendar
Thai lunar calendar
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.
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.
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
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 welldesigned one can accurately tell time to the minute." (Mayall, 1994)
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
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
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.
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.
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.)
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.
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.
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
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.
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.
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.
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
The polar dial is a directional dial.
How to make your own Sundial