Astronomers are clamoring to see this light, so NASA is obliging them by building the James Webb Space Telescope. The Webb will operate 1 million miles from Earth in a gravity-tethered spot called the L2 point, where the telescope can get cold enough that its own heat won't drown out faint traces of infrared radiation—once-visible light that's been stretched out by the universe's expansion. To ensure it will survive out there, this astro-time machine has to be prechilled: In the past year, NASA engineers have tested individual components in vacuum chambers that reach L2-like temperatures (below 50 Kelvin). Once in place, the Webb, with its 21-foot mirror, will be 100 times more powerful than the Hubble Space Telescope, able to capture images of very dim, very old light. It will also probe the atmospheres of exoplanets to check for oxygen, water, and maybe even alien pollution. Final assembly begins in December, and the fully built Webb launches from French Guiana in October 2018—heading far out in space to peer back in time.