line of apsides

astronomy

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June 18, 2026

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In astronomy, the line of apsides is the major axis of an elliptical orbit. It connects the two points on the orbit that are closest to and farthest from the central body being orbited. The point nearest the focus is called the pericentre or periapsis, and the farthest point is the apocentre or apoapsis. Specific terms are used depending on the central body, such as perihelion and aphelion for orbits around the Sun, and perigee and apogee for orbits around the Earth.12

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The line of apsides, connecting the two points, is the major axis of the orbit. The point nearest the focus is the pericentre, or periapsis, and that farthest from it is the apocentre, or apoapsis. Specific terms can be used for individual bodies: if the Sun…
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The line of apsides, connecting the two points, is the major axis of the orbit. The point nearest the focus is the pericentre, or periapsis, and that farthest from it is the apocentre, or apoapsis. Specific terms can be used for individual bodies: if the Sun…
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orbit
…Sun and is called the line of apsides or major axis of the orbit; one-half this line’s length is the semimajor axis, equivalent to the planet’s mean distance from the Sun. The eccentricity of an elliptical orbit is a measure of the amount by which it deviates from a circle;…
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…Sun and is called the line of apsides or major axis of the orbit; one-half this line’s length is the semimajor axis, equivalent to the planet’s mean distance from the Sun. The eccentricity of an elliptical orbit is a measure of the amount by which it deviates from a circle;…
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