Can China's new Xuntian Space Telescope rival NASA's Webb?

It's slated to launch in 2023.
Brad Bergan
An artist's impression of China's Space Station Telescope.China National Space Administration

Will NASA's James Webb Space Telescope have a new rival?

Anything's possible.

After all, China is launching a giant flagship telescope at the end of 2023, with aims to shed light on discoveries about galaxy evolution, in addition to uncovering riveting secrets about dark matter, and dark energy, according to a press release from a state-funded media source in China.

Called the Chinese Space Station Telescope (CSST), or Xuntian — which means "survey to heavens" in Mandarin, the observatory will be space-based, and use optical instruments to give astronomers a means to survey the sky and build a new cosmic map of the universe.

But can will it rival NASA's newest space observatory, the James Webb Space Telescope?

Scroll around, find out.

China's Xuntian space telescope sees a 350-times wider field of view than Hubble

The CSST is as long as a three-story building is tall and features a 6.5-ft (2-m) aperture. This is a bit thinner than the Hubble Space Telescope, but it makes up for this with a field of view that's 350 times larger than Hubble's, according to Deputy Director Liu Jifeng of the National Astronomical Observatories of China (NAOC).

"The field of view is the area of the sky a telescope can see at one time," said Project Scientist Li Ran of CSST's Scientific Data Reduction System, in the release. Hubble has a field of view that's roughly 1 percent of the size of a fingernail at a single arm's length, which leaves out much of the sky, argued Li. And they're right — it's part of why the James Webb Space Telescope was designed, launched, and put into position orbiting the second Lagrange point: So it can observe the entire sky.

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The CSST has a three-mirror anastigmat design capable of achieving high image quality within this large field of view. China's flagship telescope is also a Cook-type, off-axis observatory capable of managing higher levels of precision in photometry, position, and shape measurements, according to the release.

"It has an advantage for survey observations since it can scan a large part of the universe fairly quickly," said Project Scientist Zhan Hu, of the CSST's Optical Facility. But does all of this beat the James Webb Space Telescope? "Webb's 'field of regard' is actually quite large," read a blog post on NASA's official website. It can view roughly 39 percent of the entire sky in a single day, and then observe the rest (yes, 100 percent) in a six-month period.

Webb and China's CSST are fundamentally different instruments

However, Webb's angular resolution (or sharpness of vision) is roughly the same as Hubble's, which could put it behind China's telescope — at least, in resolution. But, because of the dense clouds of dust, gas, and other material in the extremely distant universe, Hubble and other optical telescopes were fundamentally limited in how far they could peer into the ancient universe — since light in the visible spectrum is interrupted by cosmic interference.

That's why Webb was designed to specialize in mid-infrared light — which can pass through much more of the universe without losing significant information (although Webb will also detect ultraviolet light). In other words, CSST will use its four instruments to observe discrete objects in the Milky Way, like star-forming areas, comets and asteroids, the evolution of supermassive black holes and galaxies, and even star formation. But these objects will have to be far closer for China's flagship telescope to see it (within or relatively near our Milky Way).

The James Webb Space Telescope, on the other hand, can peer at the very beginnings of galaxy and star formation in the universe, not long after the Big Bang itself. All this to say that Webb and China's CSST are fundamentally different kinds of highly complex scientific instruments, which is actually good! It would be unfortunate (and perhaps a waste of precious peacetime collaboration for the international science community) for two major flagship space-based telescopes to compete in research, studying the same parts of the universe, when there's so much more to see — in CSST's case, the near-ultraviolet band of the universe.

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