Monday, 30 June 2014

The Earth reaches its aphelion.

At midnight between Thursday 3 and Friday 4 July 2014 the Earth will reach its aphelion, the furthest point in its orbit from the Sun, a distance of 152 093 481 km. 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 152 097 427 km from the Sun on 5 July.

Graphic showing the eccentricities of Mercury, Earth and Mars; the dotted lines represent a circular orbit centered on the Sun, the solid lines the actual orbit. Spaceweather.

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.

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...


An Annular Eclipse will occur on Tuesday 29 April 2014, starting at about 3.52 am GMT. It will be visible from Australia, much of Antarctica and the southern Indian Ocean, eastern Java and the islands of the Bali, Flores and Savu Seas, though a full Annular...



A total Lunar Eclipse will occur on 15 Aril 2014, starting at about 4.35 am GMT. It will be visible across much of Canada and the United States, as well as all of Mexico and Central America, western South America and many Pacific and Caribbean Islands. Part of the eclipse will be visible from remaining areas of the Americas as...




The planet Mars will make its closest pass to the Earth since December 2007, coming within 92 000 000 km of us on 14 April 2014. This will make the planet a particularly bright object, visible in the night sky from anywhere on Earth in the constellation of Virgo, close to...


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