from The American Heritage® Dictionary of the English Language, 4th Edition
- n. The point on the orbit of a celestial body that is farthest from the sun.
from Wiktionary, Creative Commons Attribution/Share-Alike License
- n. The point in the elliptical orbit of a planet, comet, etc., where it is farthest from the sun.
from the GNU version of the Collaborative International Dictionary of English
- n. That point of a planet's or comet's orbit which is most distant from the sun, the opposite point being the perihelion.
from The Century Dictionary and Cyclopedia
- n. That point of a planet's or of a comet's orbit which is most distant from the sun: opposed to perihelion.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
- n. apoapsis in solar orbit; the point in the orbit of a planet or comet that is at the greatest distance from the sun
In order for this result to be produced, the earth must reach that part of its orbit known as aphelion, where the distance from its controlling centre is greatest, so that the eccentricity of the moon's orbit is always an indication of the position of the earth in its relation to the sun.
At the opposite point of its orbit, where it will be in "aphelion," or farthest from the sun, the sun will only appear about 19 minutes in diameter.
The first colonists arrived only to learn that they had to contend with a winter twenty times the duration of summer and so extreme it froze the atmosphere to the surface well after aphelion to the primary.
Criminy, I almost forgot: on July 4th, at roughly 08: 00 UT, the Earth was at aphelion.
So whether or not Pluto is moving towards perihelion or aphelion that doesn't determine its "spring" or "autumn", does it?
Comets, with their hugely eccentric orbits, may pass far beyond the outer planets to spend their aphelion in the vast interstellar darkness beyond the Kuiper Belt .
In 12,900 years, the North will have colder winters because Earth will be furthest from the Sun (aphelion) in January.
When the orbit is more elliptical, the perihelion is closer to the Sun and the aphelion is farther away than when the orbit is more circular.
Scotsman James Croll combined the eccentricity of the orbit and the precession and in the 1860s and 1870s presented his ideas on the effects of the cycles and how they might influence climate, especially the colder winters when they correspond with the aphelion.
Figure 1: Position of the equinoxes, solstices, aphelion, and perihelion on the Earth's orbit.