Why put a telescope at the Lagrange Point L2

Lagrange points are areas in space where the gravity and orbital motions of nearby bodies come into balance. There are five Lagrange points around the Earth; the Webb telescope will be located in the L2 point, 940,000 miles (1.5 million km) from Earth.

At L2, the Earth’s gravity will pull Webb along, so it can “keep up” with Earth in its path around the Sun. This is important because Webb has to be kept in a very specific position that allows its sunshield to protect it from light from the Sun, Earth and Moon at the same time. At the L2 point, the Sun and Earth will always be lined up on the other side of Webb's sunshield.