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Friday, 20 January 2012

Aphelion-perihelion and perigee-apogee (Astroinfo)

Aphelion - perihelion and perigee - apogee. Both mean different things.
Perihelion and aphelion is about the minimum and maximum distance between Earth and Sun, and the perigee and apogee, referring to the minimum and maximum distance between the Moon and Earth.

Distance between Earth and Sun
The average distance is about 150 million kilometers (149.6). This distance of 149.6, is defined as an astronomical unit or 1 AU, and is equal to about 8.2 light minutes, because light from the Sun, have about 8 minutes to reach the Earth.

Earth orbit is not perfectly circular in fact, so that the distance between Earth and Sun varies slightly over the year, from a minimum of 147,100,000 km to a maximum of 152,100,000 km.

So semi-major axis of Earth's orbit is 149597887.5 km (149.6). When closest to the Sun (or perihelion), the planet is 147,098,074 km, or 0.98 AU. At the farthest point from the Sun (or aphelion) is 152,097,701 km or 1.02 AU.
We are the furthest from the Sun during summer in the northern hemisphere, around July 4, and the nearest, around January 4, when on the southern hemisphere summer.


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