Java Reference
In-Depth Information
A lunar calendar is based on lunar phase cycle. It is not aligned to a tropical year. In a year, it drifts by 11 to 12 days
from a tropical year. A lunar calendar takes about 33 years to catch up with a tropical year, to drift again for another
33 years. A lunar month, which is also called a synodic month, is the interval of time between new moons that is equal
to 29 days, 12 hours, 44 minutes, and 2.8 seconds. The Islamic calendar is an example of a lunar calendar.
A lunisolar calendar computes months based on lunar phase cycle like a lunar calendar. However, it intercalates,
in a 2-year or 3-year period, a month to keep itself aligned with a tropical year. The Buddhist, Hindu lunisolar,
Chinese, Hebrew calendars are some examples of lunisolar calendars.
The Julian Calendar
The Julian calendar is a solar calendar introduced in the year -45 by Julius Caesar. It was widely used by the European
civilization until year +1582 when the Gregorian calendar was introduced.
An ordinary year consists of 365 days. Every four years, a day is intercalated between February 28 and March 1,
which is designated as February 29, to make the year 366 days, which is called a leap year. The year 0 (1 B. C.)
is considered a leap year. The average length of a Julian calendar year is 365.25 days that is close to the length of a
tropical year known in those days.
A year consists of 12 months. Months are fixed in lengths. Table
12-1
lists the order, name, and number of days in
months in the Julian calendar.
Table 12-1.
Order, Name, and Number of Days in Months in Julian and Gregorian Calendars
Order
Month Name
Number of Days
1
January
31
2
February
28 (29 in a leap year)
3
March
31
4
April
30
5
May
31
6
June
30
7
July
31
8
August
31
9
September
30
10
October
31
11
November
30
12
December
31
The Gregorian Calendar
The Gregorian calendar is the most widely used calendar in the world for civil purposes. It follows the rules of the
Julian calendar for number of months in a year and number of days in months. However, it changed the rule for
computing a leap year: a year is a leap year if it is exactly divisible by 4. A year exactly divisible by 100 is not a leap year
unless it is also divisible by 400.
