Plural of apoapsis; the points in orbits of celestial bodies that are farthest from the center of attraction.
From Greek 'apo-' (away from) + 'apsis' (orbit point). Used in astronomy and orbital mechanics.
When a satellite reaches its apoapsides—the farthest points from Earth—it moves slowest in its orbit, which is why astronauts perform important maneuvers at these distant points.
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