James Webb Space Telescope’s groundbreaking optics explained by NASA
The James Webb Space Telescope suffers from astigmatism, but that visual condition is a very good thing for astronomy, NASA assures us.
A new explainer video the agency posted on YouTube talks about the huge telescope’s optics and how they will let astronomers peer deep into the universe’s history for future science work, ranging across subjects from exoplanets to the formation and evolution of early galaxies.
“This type of telescope enables a wider field of view and minimizes optical distortions,” Sophia Roberts, a producer at NASA’s Goddard Space Flight Center in Maryland, explains in the video.
Live updates: NASA’s James Webb Space Telescope mission
The James Webb Space Telescope’s 21.3-foot (6.5 meter) diameter primary mirror, seen deployed during testing here on Earth. (Image credit: NASA/Chris Gunn)
Webb launched on Dec. 25, 2021 and is scheduled to begin science operations this summer.
The observatory will capture light with its 21.3-foot-wide (6.5 meters), 18-segment primary mirror, reflecting it to a much smaller secondary mirror. The light will then continue to bounce, moving next to a tertiary mirror and at last to a flat, fine steering mirror.
The steering mirror next pinpoints the light through a hole in the center of the primary mirror, relaying the signal to the science instruments. It’s pretty close to a typical Cassegrain telescope design on Earth, Roberts explains in the video, although the telescope has the additional challenge of being large and having to work in extremely cold conditions in space.
Webb gets around this coldness issue in part by having its mirrors made of beryllium, Roberts explains, “because this chemical element is very strong, lightweight and virtually ceases changing shape when it gets really cold.” Additionally, the mirror segments include a thin coating of pure gold (less than 100 atoms thick) to reflect the infrared light on which Webb will focus.
Webb will take several months to cool to its operational temperature; it needs to be very cold to observe in infrared light, with a minimum of interference from the environment or from its four science instruments. The mission team also needs to finish aligning the primary mirror segments and check out Webb’s instruments before the observatory can begin its science work.