equation of light

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The correction required to account for the time that light takes to cross the orbit of the Earth. Light takes almost exactly 499s to travel from the Sun to the Earth, so that the time recorded for an event, such as an occultation, could vary by over 16½ minutes depending on where the Earth lies in its orbit. For events outside the Solar System, it is common to record timings as though they had been made from the Sun (heliocentric time). Within the Solar System, such as when timing eclipses of a planet's satellites, not only the position of the Earth needs to be taken into account but also that of the planet, and those of the satellites.

Subjects: Astronomy and Astrophysics.

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