Heliocentric Julian Day
Julian Date corrected for differences in the Earth’s position with respect to the Sun
The Heliocentric Julian Date (HJD) is the Julian Date (JD) corrected for differences in the Earth's position with respect to the Sun. When timing events that occur beyond the Solar System, due to the finite speed of light, the time the event is observed depends on the changing position of the observer in the Solar System. Before multiple observations can be combined, they must be reduced to a common, fixed, reference location. This correction also depends on the direction to the object or event being timed.
Magnitude and limitations
The correction is zero (HJD = JD) for objects at the poles of the ecliptic. Elsewhere, it is approximately an annual sine curve, and the highest amplitude occurs on the ecliptic. The maximum correction corresponds to the time in which light travels the distance from the Sun to the Earth, i.e. ±8.3 min (500 s, 0.0058 days).
JD and HJD are defined independent of the time standard. Rather, JD can be expressed as e.g.
“Heliocentric Julian Day” enters the record as julian Date corrected for differences in the Earth’s position with respect to the Sun. Crown Archives preserves that source wording while asking what Heliocentric, Julian and Date can confirm, complicate or overturn.
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This entry incorporates text from “Heliocentric Julian Day” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.