是日地球通過遠日點

[社長]

Today the Earth is at its furthest position from the Sun - the Aphelion.

http://www.facebook.com/photo.php?fbid= ... e=1&ref=nf

The Earth orbits the Sun in an elliptical orbit (eccentricity=0.0167). Unlike a perfect circular orbit (e=0), the foci of an ellipse are not at the center. Therefore, the distance between the Earth and the Sun varies from time to time. The closest point is called the Perihelion, and the furthest point is called the Aphelion.

But WAIT.......if aphelion is the furthest point, why is it Summer now (for northern hemisphere) and not Winter? How can it be hotter when the Earth is further?

FACT: The existence of seasons are due to the tilt of the Earth's axis (23.4 degrees from the perpendicular to the Earth–Sun plane), and not its distance from the Sun.

The Earth is at its aphelion in July every year, when the northern hemisphere is tilted towards the Sun, while it will be at its perihelion in Jan every year, when the northern hemisphere is tilted away from the Sun.