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Aladin Lite
HJD/BJD
Heliocentric Julian Date
Heliocentric Julian Date (HJD) is the Julian Date (JD) corrected for the effects of the Earth's
motion around the Sun. It accounts for the light travel time between the Earth and the Sun by
shifting the observer's position to the Sun's center, which helps in more accurate timing of
astronomical events, especially when observing distant celestial objects like stars or
exoplanets. HJD removes the small variations caused by the Earth's movement, providing more
precise measurements of the timing of events as seen from the Sun's reference frame.
Barycentric Julian Date
Barycentric Julian Date (BJD) is the Julian Date (JD) corrected for the motion of the observer
relative to the center of mass of the Solar System, known as the barycenter. This correction
accounts for both the Earth's motion and the influence of other planets, ensuring highly precise
timing of astronomical events, particularly for distant objects. BJD is more accurate than HJD
because it considers the gravitational effects of all massive bodies in the Solar System, making
it essential for timing sensitive measurements like exoplanet transits and pulsar timings.