Question 1

What is Julian Date?

Accepted Answer

Julian Date (JD) is a continuous count of days since the beginning of the Julian Period on January 1, 4713 BC at noon Universal Time. It is widely used in astronomy.

Question 2

What is Modified Julian Date (MJD)?

Accepted Answer

Modified Julian Date (MJD) is Julian Date minus 2400000.5. It starts at midnight instead of noon and uses smaller numbers for convenience.

Question 3

What is J2000.0?

Accepted Answer

J2000.0 is a standard astronomical epoch corresponding to Julian Date 2451545.0, which is January 1.5, 2000 (noon on January 1, 2000 UTC).