185°F vs −388°F on the Same Telescope - Video

Number one: about 185°F (85°C), the sunlit, hot side of NASA's James Webb Space Telescope, near boiling. Number two: about −388°F (−233°C), the shaded, cold side of the same telescope. For comparison, the coldest temperature ever recorded on Earth, at Vostok station in Antarctica, was −129°F (−89°C), which NASA calls far too toasty for Webb. What holds back a difference of about 570°F? Webb's tennis-court-sized sunshield: five layers of Kapton, a tough plastic coated with reflective metal, each thinner than a human hair. The layers don't touch, heat radiates out of the gaps between them, each layer is cooler than the one below, and the vacuum in between is a very good insulator. Why bother? Webb observes in infrared light, which is essentially heat, so to detect the extremely faint heat of very distant objects the telescope itself has to be kept very cold. Shown: Webb fully assembled and in cryogenic testing, its sunshield layers and test unit, and its gold-coated primary mirror (NASA photos), an Antarctic landscape from NASA's Operation IceBridge, and an infrared galaxy image from NASA's Spitzer Space Telescope (illustrating infrared light; not a Webb image).

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Fact sources:
- NASA Science — How Does Webb Stay Cold?: https://science.nasa.gov/mission/webb/science-overview/science-explainers/how-does-webb-stay-cold/
- NASA Science — Webb's Sunshield: https://science.nasa.gov/mission/webb/webbs-sunshield/
- NASA Science — Webb Overview: https://science.nasa.gov/mission/webb/about-overview/

Imagery credits (NASA media is public domain; NASA does not endorse this channel):
- NASA’s Webb Telescope Completes Goddard Testing: NASA (GSFC) (Public domain) https://images.nasa.gov/details/GSFC_20171208_Archive_e000079
- NASA's Webb Telescope "chilling out" in Houston for the summer: NASA (GSFC) (Public domain) https://images.nasa.gov/details/GSFC_20171208_Archive_e000032
- Mountain Peaks: NASA (GSFC) (Public domain) https://images.nasa.gov/details/GSFC_20171208_Archive_e000911
- A Mechanical Harmony to NASA's Webb Telescope Sunshield: NASA (GSFC) (Public domain) https://images.nasa.gov/details/GSFC_20171208_Archive_e000209
- NASA's Webb Sunshield Stacks Up to Test: NASA (GSFC) (Public domain) https://images.nasa.gov/details/GSFC_20171208_Archive_e001023
- Final Sunshield Layer Completed for NASA’s James Webb Space Telescope: NASA (GSFC) (Public domain) https://images.nasa.gov/details/GSFC_20171208_Archive_e000189
- JWST's Golden Mirror Revealed: NASA (GSFC) (Public domain) https://images.nasa.gov/details/GSFC_20171208_Archive_e000368
- The Swirling Arms of the M100 Galaxy: NASA/JPL-Caltech (Public domain) https://images.nasa.gov/details/PIA15910

Narration: AI-generated voice (text-to-speech). Script written and fact-checked by the channel.

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