This point is called Lagrange Point Number 2 or simply 'L2'. There are a total of 5 such points defined in the so-called restricted 3-body problem. This is the situation where you have two massive bodies like the Sun and Earth, or the Moon and Earth, in orbit around each other. The third body is one with substantially less mass than the other two, such as a moon, a man- made satellite, or even an asteroid.
In the Earth-Moon system, the L2 point for an Earth-orbiting satellite is, at any instant in time, located on the line that joins the center of the Earth with the center of the Moon. The distance of this point from the center of the Earth is given by:
d = a + 1/3 (a^2) + 1/9 (a^3)
where a = the cube root of 1/3 times the ratio of the mass of the Moon (m) divided by the mass of the Earth (M), i.e.
a = (m/3M)^1/3 = (1.0/81 x 1/3)^1/3 = 0.16
so d = 0.16 + .0085 + 0.00045 = 0.169
L2 is located 0.169 times the Earth-Moon distance from the Earth, or 0.169x384,400 km = 64,946 km (41,565 miles) from the center of the Earth along the Earth-Moon line.
Visit the NASA, MAP mission page to learn more about the Earth-Sun Lagrange Points.
Copyright 1997 Dr. Sten Odenwald
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