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The aphelion distance between the Earth's and Sun's centers is currently about 1.016 71 AU or 152,097,700 km (94,509,100 mi). The dates of perihelion and aphelion change over time due to precession and other orbital factors, which follow cyclical patterns known as Milankovitch cycles.
The changing Earth-Sun distance results in an increase of about 7% in total solar energy reaching the Earth at perihelion relative to aphelion. Since the southern hemisphere is tilted toward the Sun at about the same time that the Earth reaches the closest approach to the Sun, the southern hemisphere receives slightly more energy from the Sun ...
The astronomical unit (symbol: au, or AU) is a unit of length defined to be exactly equal to 149,597,870,700 m. Historically, the astronomical unit was conceived as the average Earth-Sun distance (the average of Earth's aphelion and perihelion), before its modern redefinition in 2012.
For Earth's current orbital eccentricity, incoming solar radiation varies by about 6.8%, while the distance from the Sun currently varies by only 3.4% (5.1 million km or 3.2 million mi or 0.034 au). Perihelion presently occurs around 3 January, while aphelion is around 4 July.
The apsidal precession is the rate of change of ω through time, d ω d t. In celestial mechanics, apsidal precession (or apsidal advance) [1] is the precession (gradual rotation) of the line connecting the apsides (line of apsides) of an astronomical body 's orbit. The apsides are the orbital points farthest (apoapsis) and closest (periapsis ...
At θ = 0°, perihelion, the distance is minimum = + At θ = 90° and at θ = 270° the distance is equal to . At θ = 180°, aphelion, the distance is maximum (by definition, aphelion is – invariably – perihelion plus 180°)
The eccentricity of an elliptical orbit can be used to obtain the ratio of the apoapsis radius to the periapsis radius: For Earth, orbital eccentricity e ≈ 0.016 71, apoapsis is aphelion and periapsis is perihelion, relative to the Sun. For Earth's annual orbit path, the ratio of longest radius ( ra) / shortest radius ( rp) is.
The maximum (instantaneous) orbital speed occurs at periapsis (perigee, perihelion, etc.), while the minimum speed for objects in closed orbits occurs at apoapsis (apogee, aphelion, etc.). In ideal two-body systems, objects in open orbits continue to slow down forever as their distance to the barycenter increases.