![]() L2 is a naturally chilly place, but Webb needs something more to push the temperature right down. And all external sources of light or heat need to be blocked out. The telescope in fact must be colder than the infrared light it is looking for in order not to distort its own observations. Webb will be seeking to detect infrared signals from the early universe – the faintest traces of long-wave heat radiation – and to do this, its instruments need to be kept incredibly cold, at about -225☌. The stable Sun–Earth–spacecraft alignment at L2 makes an ideal home environment for Webb, well worth the month-long, 1.5 million km journey. So Webb will loop around L2 in a six-month elliptical orbit at several thousand km, calculated so that the spacecraft is never in the shadow of the Earth (or the Moon) during the mission. However, a spacecraft stationed precisely at the L2 point would find that the Earth partially blocks the Sun, and this would reduce the amount of power available for the solar arrays. Thus it maintains a fixed position relative to both the Earth and the Sun (with minimal adjustments and therefore limited fuel expenditure), moving in lockstep with the Earth on its orbital journey around the Sun like a sidecar on a motorcycle. L2 is one of five remarkable locations in the Sun–Earth system where the competing gravity forces of these two bodies counterbalance each other, so that a smaller object – such as a spacecraft – put there is “held in place” by the gravity pull equilibrium created.
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