The Gregorian Calendar did not exist prior to October 15, 1582, so
dates displayed before that are meaningless. British countries (including
what later became the United States) had previously used March 25 as New
Year's Day and the Julian calendar and they accepted the Gregorian
calendar in 1752. Thus, George Washington was actually
born on Feb. 11, 1731, Old Style (O.S.); his birthday became Feb. 22, 1732,
Gregorian, or New Style (N.S.) (the date we celebrate).
This is a true solar calendar. But it has special rules for establishing when Easter occurs which is dependent also on the Moon.
Septuagesima is 63 days or 9 weeks before Easter.
Quinquagesima is 49 days before Easter.
Ash Wednesday is the beginning of Lent at 46 days before Easter.
Palm Sunday begins Passion Week at 7 days before Easter.
Good Friday is 2 days before Easter.
Rogation Sunday is 35 days after Easter.
Ascension is 39 days after Easter.
Pentecost is 49 days after Easter.
Trinity Sunday is 56 days or 8 weeks after Easter.
Corpus Christi is 60 days after Easter.
Christmas is on December 25.
The Julian Calendar was initially a modification (adding in leap
days every four years) of the Roman
AUC calendar in 46 BC (which was 708 AUC, the number of years
from the beginning of the Roman Empire). That year was the longest
year ever, as the Emperor Julius Caesar declared it to have 445 days
so that the seasons again matched up properly! It became a Christian
calendar in what we now call 525 AD when a Monk decided to base
the calendar on the date of the Birth of Jesus. (Therefore the year
numbers given here did not exist prior to 525 AD, and the year numbers
actually used were still then in the AUC calendar, where the number was
754 higher - so 525 AD was actually then known as 1279 AUC.) His calculations
were close but we now believe that Jesus was Born early in what we
would now call 4 BC. This Christian-modified Julian calendar
gradually became used world-wide in the centuries after 525 AD, until the
more accurate Gregorian calendar replaced it a thousand years later (in most
places) due to improved accuracy regarding Leap Years and the seasons. The
Orthodox Church still uses this calendar but virtually no one else does.
It is currently about 13 days different from the Gregorian calendar.
Triodon begins at 70 days or 10 weeks before Orthodox Easter.
First Saturday of Souls is 57 days before Orthodox Easter.
Lent begins on Monday at 48 days before Orthodox Easter.
Sunday of Orthodoxy is 42 days before Orthodox Easter.
Palm Sunday begins Passion Week at 7 days before Orthodox Easter.
Holy (Good) Friday is 2 days before Orthodox Easter.
Ascension is 39 days after Orthodox Easter.
Pentecost is 49 days after Orthodox Easter.
All Saints Day is 56 days or 8 weeks after Orthodox Easter.
Christmas is on December 25.
The Islamic Calendar begins with the Western (Julian) date of July 16,
622 AD, which is referred to as Muharram 1, 1 AH. Dates displayed
before that are therefore meaningless.
It is a purely lunar calendar
New Years Day is Muharram 1
Ashura is Muharram 10
Mawlid is Rabi'I 12
The Hajj pilgrimage is to be done during the last lunar month of the year, Dhu al-Hijja.
The month of Ramadan involves fasting regarding eating, drinking and smoking, from dawn to the moment of sunset.
The Night of Determination occurs on the night of Ramadan 26, during which, the Koran says that God/Allah determines the course of the world for the following year.
Eid al-Fitr begins on Shawwal 1, and lasts for three days, is the Feast of Fast-Breaking and is celebrated with special prayers and festivities.
Eid al-Adha begins on Dhul-Hijjah 10, and lasts for three days, marks the end of the Hajj, the Festival of the Sacrifice.
The Hebrew Calendar is based on the concept that the Universe was
created in October, 3761 BC, and so all dates are based on that.
It is a lunisolar calendar. It is a complex system, where a year can have any of six different numbers of days in it (353, 354, 355, 383, 384, or 385) and referred to as 'deficient, regular or complete' and 'common (350s) or embolismic (380s)'.
Rosh Hashanah is the Jewish New Year, at Tishri 1, but only on a Monday, Tuesday, Thursday or Saturday, so it can be delayed.
Fast of Gedalya is Tishri 2.
Yom Kippur is the Day of Atonement at Tishri 10, except never on Friday or Sunday.
Sukkot is Tishri 15.
Shemini Atzeret is Tishri 22.
Hanukkah begins Kislev 25, and continues for a total of eight days.
Tu B'Shvat is Teveth 27.
Ta'anis Esther is the Fast of Esther at Adar 25.
Purim is Adar 26.
Pesach is Passover at Nisan 15.
Shavuot is Jewish Pentecost at Sivan 6.