Lagrange points

A space telescope is always placed at one of the five Lagrange points in the Sun-Earth system. These are especially advantageous in terms of energy and facilitate an insight into a particular part of the sky. Lagrange points are mathematically calculable locations at which the gravitational pull of the Earth and the Sun are equalised. A telescope therefore hardly needs any fuel at this point, as their orbit is synchronous to that of the Earth around the Sun.

L1 and L2 are particularly relevant for observing the sky. As both are not stable in the direction of the Sun and Earth, telescopes circle around them in complicated orbits. L1 allows a good view of the Sun. At L2, sensitive devices are protected from solar radiation and have a clear view into space without the Earth getting in the way.

In the diagram, the Sun is shown in yellow, the Earth to the right of it in blue and the Lagrange points in red.

The Jupiter-Sun system is also an interesting field of experimentation for Lagrange points, as the planet is so large compared to all other objects in the Solar System.