Definition of aphelion in English:



  • The point in the orbit of a planet, asteroid, or comet at which it is furthest from the sun.

    ‘Mars is at aphelion’
    The opposite of perihelion
    • ‘This affects the climate because the influx of solar energy to our planet would then vary between perihelion and aphelion by a larger proportion than at present.’
    • ‘Furthermore, any resonance with the Earth is illusory in that Mercury is not well placed for observations except during its brief greatest elongations near its aphelion.’
    • ‘Variations in the timing of perihelion and aphelion are caused by a ‘wobbling’ in the Earth's axis of rotation as it rotates around the Sun.’
    • ‘There are small cyclic variations in those apparent sizes because the Earth-Moon distance changes as the latter moves between perigee and apogee, and the Earth-Sun separation alters as the former moves between perihelion and aphelion.’
    • ‘This is because at aphelion the planet is moving slowest, and consequently it is less likely to pass across the Sun during the critical window.’


Mid 17th century: alteration of modern Latin aphelium (by substitution of the Greek inflection -on), from Greek aph' hēlion from the sun.