Telescopes from the Ground Up

Seeing the invisible

The James Webb Space Telescope, scheduled to launch later this decade, is NASA's largest observatory yet.

Webb, like the Spitzer Space Telescope, will view the universe in wavelengths that cannot be seen by the human eye. Webb will observe infrared light. Objects that are not quite hot enough to glow with visible light glow with infrared light. Infrared light also pierces layers of dust that can hide objects in space, allowing Webb to see objects that would normally be blocked from view.

Long time traveling

Infrared astronomy is important because light from the most distant objects in space is also light that started traveling billions of years ago. Because the universe is expanding, visible light gets stretched as it travels through space, turning it into infrared light.

Earth’s atmosphere blocks most infrared light coming from space. In addition, sources of infrared light on Earth interfere with observations. These factors make it difficult to do infrared astronomy on our planet. Some infrared telescopes are positioned on mountaintops, where the atmosphere is thin, but one of the best places to do infrared astronomy is in space.

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Space Telescopes
Diagram of the orbit of the Webb Space Telescope in orbit with Earth around the Sun.
Illustration of the Webb Space Telescope in orbit with Earth around the Sun.Enlarge picture
The Webb Space Telescope
Launch: Later this decade
Telescope type: Reflector
Light collector: Gold-coated beryllium mirror
Mirror diameter: 255.6 inches
(6.5 m)
Light observed: near- to mid-infrared
Discovery Highlights:
  • Telescope has not launched.