Imagine trying to read a very old letter, written when the universe was still young. The James Webb Space Telescope, often called Webb, is built for that kind of search. NASA describes it as a large space observatory optimized for infrared light. Its primary mirror is about six and a half meters wide and is made of eighteen segments. A large sunshield blocks heat from the Sun, Earth, and Moon. Webb works near the second Lagrange point, more than a million kilometers from Earth, where it can keep its instruments extremely cold.