Earth in aphelion on July 4th
Publiée le 2008-07-02
(perihelion) and a maximum (aphelion). The Earth will pass to its aphelion on July 4th, 2008 at 7h 40min 54s UTC. The Earth-Sun distance will be then of 1,016753512046ua is exactly 152,104160419735Mkm . This maximum value is not the same year after year because the Earth orbit is not a perfect ellipse but an ellipse perturbed by the gravitational effects.
It can appear paradoxical that this maximum distance from the Sun is reached whereas we are in summer and the weather is hot in our hemisphere. This is due to the inclination of the rotation axis of the Earth with respect to the perpendicular of its orbit plan (the ecliptic). At the summer solstice (on June 20th in 2008), a date close to the passage of the Earth at aphelion, the Sun passes to the zenith of the tropic of Cancer. In Northern hemisphere the elevation of the Sun on the horizon and the duration of its illumination are then maximum. This effect contributes more to the climate than the distance to the Sun. The seasons are reversed between Northern hemisphere and Southern hemisphere. However it is false to believe that for our hemisphere, the fact that the Earth is at aphelion in summer and at perihelion in winter (towards January the 4th) would moderate the contrast of the seasons then would amplify it in southern hemisphere. It is also erroneous of saying that the day of the summer solstice is the day when the Sun culminates with its higher elevation in the Northern hemisphere! That is true only for the places located at the North of the Cancer tropic. The date of passage of the Earth in perihelion and that of passage in aphelion advance in our calendar. In this way in approximately 9.800 years, the Earth will pass in perihelion on June 21th at the time of the summer solstice.
The orbit of the Earth-Moon barycentre around the Sun is, at first approximation, an ellipse. The Earth-Sun distance is not constant and presents a minimum |