Monday, 6 July 2015

Earth reaches aphelion.

The Earth will reach its aphelion, the furthest point in its orbit from the Sun, a distance of 152 093 481 km, at 7.41 pm GMT on Monday 6 July 2015. The Earth's orbit is slightly eccentric and slightly variable, leading to the distance between the Earth and the Sun varying by about 3.4% over time, reaching aphelion early in July each year and perihelion (the closest point on its orbit to the Sun) early in January. The exact distance at aphelion and perihelion each year varies, with this year's aphelion being slightly closer to the Sun than last year's, when the Earth reached 152 093 403 km from the Sun on 4 July.

The difference between the Earth's perihelion (closest point to the Sun) and aphelion (furthest point from the Sun). Time and Date.

This is counter intuitive to inhabitants of the Earth's Northern Hemisphere, who often assume that the Earth is closest to the Sun in midsummer, when in fact it is at its furthest away. This is because the tilt of the Earth plays a far greater role in our seasons than the distance from the Sun, and the Northern Hemisphere has just passed its Summer Solstice, i.e. the point at which the North Pole was pointing as close to the Sun as it ever gets, so that the Northern Hemisphere is currently getting much more sunlight than the Southern. The Earth's surface receives about 7% less sunlight at aphelion to at perihelion, but this is far less than the seasonal variation caused by the tilt of the Earth (23% in each hemisphere).

In fact the Earth could potentially move quite a bit in its orbit and still maintain an equitable climate, possibly even if it was as far out as Mars (1.5 AU), though presumably this would be somewhat cooler. Mars is a frozen wasteland largely because it is small and airless. The Earth, being larger, is able to sustain a thicker gaseous atmosphere, leading to a greenhouse effect that keeps the planet warm. Probes on the Red Planet have found abundant geological indicators of running water on the surface, suggesting that ancient Mars had a thicker atmosphere which could support liquid water, but this has now gone, the low gravity of the planet having let it escape molecule by molecule.

See also...

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