Tuesday, 5 July 2016

Earth reaches its aphelion.

The Earth reached its aphelion, the furthest point in its orbit from the Sun, a distance of 152 111 120 km, at 4.24 pm GMT on Monday 4 July 2016. 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 further the Sun than last year's, when the Earth reached 152 093 481 km from the Sun on 6 July. In three years time, on 4 July 2019 the Earth will reach its furtherst point from the Sun this century, at a distance of 152 114 291 km.

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...

http://sciencythoughts.blogspot.co.uk/2016/06/the-june-solstice.htmlThe June Solstice.                                         The June (or Northern) Solstice falls on Monday 20 June in 2016, the day on which the Sun rises highest in the sky and the longest day of the year in the Northern Hemisphere (where it is the...
http://sciencythoughts.blogspot.co.uk/2016/03/march-equinox-2016.htmlMarch Equinox, 2016.                                  The March Equinox fell on 20 March this year. The Earth spins on its...
http://sciencythoughts.blogspot.co.uk/2015/12/the-2015-december-solstice.htmlThe 2015 December Solstice.                       The December (or Southern) Solstice this year falls on Tuesday 22 December, when the Sun is at its southernmost point in the sky. This is the shortest day of the year in the Northern Hemisphere, where it is known as the Winter Solstice and the longest day in...
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