The Julian Day Number (JDN) is an integer representing a whole solar day, starting from
noon Universal Time on Monday, January 1, 4713 BC (November 24, 4714 BC, in the
proleptic Gregorian calendar). For example, the Julian day number for noon UT on January
1, 2000, was 2,451,545.
What is Gregorian Date?
The Gregorian calendar is the most widely used calendar worldwide, introduced by Pope
Gregory XIII in October 1582. It adjusts for leap years, making the average year
365.2425 days long to match the Earth's orbit around the Sun.
What is the difference between Julian Date and Gregorian Date?
The Julian calendar, proposed by Julius Caesar in 46 BC, was used until 1582. The
Gregorian calendar, introduced in 1582, is more accurate, with leap years occurring
every four years, except for years divisible by 100 but not by 400.
What is the difference between Julian Date and Julian Day Number?
The Julian Day Number (JDN) is an integer representing a whole solar day, while the
Julian Date is the fractional part of the day. Both are based on the Julian day count
starting from noon UT on Monday, January 1, 4713 BC.
What is the Moon phase, age, distance, and lunation number?
The Moon's phase is the shape of its sunlit portion as seen from Earth, changing as it
orbits Earth. The Moon's distance from Earth varies, ranging from about 363,300 km at
perigee to 405,500 km at apogee. The lunation number is a long-term cycle used to track
the Moon's position in the sky, approximately 19 years long.