astronomy

Xuntian

Xuntian is a astronomy topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Xuntian rather than just read about it. In short: The Xuntian (Chinese: 巡天; pinyin: Xúntiān; lit. 'Tour of Heaven') or Chinese space station survey telescope (CSST) (Chinese: 巡天空间望远镜; pinyin: Xúntiān Kōngjiān Wàngyuǎnjìng) is a Chinese space telescope under development. The telescope will feature a 2-metre-diameter (6.6-foot) primary mirror and is expected to have a field of view approximately 300 to 350 times larger than that of the Hubble Space Telescope.

Key takeaways

Xuntian belongs to astronomy; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Xuntian to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Xuntian from memory before moving on to harder problems.

Reference excerpt

The Xuntian (Chinese: 巡天; pinyin: Xúntiān; lit. 'Tour of Heaven') or Chinese space station survey telescope (CSST) (Chinese: 巡天空间望远镜; pinyin: Xúntiān Kōngjiān Wàngyuǎnjìng) is a Chinese space telescope under development. The telescope will feature a 2-metre-diameter (6.6-foot) primary mirror and is expected to have a field of view approximately 300 to 350 times larger than that of the Hubble Space Telescope. Its 2.5-gigapixel camera is designed to survey up to 40% of the sky. As of 2026, Xuntian is scheduled for launch in 2027 aboard a Long March 5B rocket. It is planned to operate in a co-orbital arrangement with the Tiangong space station, allowing periodic docking for servicing and maintenance.

Overview

The telescope uses an unobstructed off-axis optical design, avoiding diffraction effects caused by mirror support structures. This design is intended to improve image quality for observations including weak gravitational lensing measurements. The primary mission consists of wide-field imaging and slitless spectroscopic surveys covering wavelengths from 255 to 1,000 nm. (Cosmological research is a major scientific objective,) particularly observations at medium and high Galactic and ecliptic latitudes. During its planned ten-year mission, the survey camera is expected to cover approximately 17,500 square degrees of sky in multiple bands, reaching point-source 5σ limiting magnitudes of about 26 (AB magnitude) in the g and r bands. The slitless spectrograph is designed to achieve an average spectral resolution of at least 200. In addition to the main survey, the telescope will observe selected deep fields to greater depth than the wide-area survey. The combination of high angular resolution, broad wavelength coverage, imaging and spectroscopic capabilities, and large survey area is intended to support studies of cosmology, galaxy evolution, and related fields. Observations from Xuntian are expected to complement data collected by other optical space telescopes, including Hubble, Euclid, and Nancy Grace Roman.

Instruments

Xuntian will have six scientific instrument bays, with plans to carry five instruments at launch:

Survey camera The survey camera (SC), also known as the multi-colour photometry and slitless spectroscopy survey module, occupies the main focal plane. It comprises a seven-band photometry subsystem (NUV, u, g, r, i, z and y) and a three-band slitless spectroscopy subsystem (GU, GV and GI). The photometry subsystem uses 18 filters and covers about 60 percent of the focal-plane area, while the spectroscopy subsystem uses 12 gratings and covers the remaining 40 percent.

Integral field spectrograph The integral field spectrograph (IFS) provides spatial resolution of 0.2 arcseconds and covers wavelengths from 0.35 to 1.0 μm. It is primarily intended for observations of compact, bright targets, including galactic nuclei and star-forming regions. The IFS can observe in parallel with the MCI.

Multichannel imager The multichannel imager (MCI) contains three channels covering wavelengths from the near-ultraviolet to the near-infrared. The channels operate simultaneously and use narrow-, medium-, and wide-band filters to conduct deep-field surveys across a field of view of 7.5′ × 7.5′. Combined observations are expected to reach depths of 29–30 AB magnitude. Planned scientific uses include studies of high-redshift galaxies, dark matter, dark energy, and calibration of photometric redshift measurements. The MCI can observe in parallel with the IFS.

Cool planet imaging coronagraph The cool planet imaging coronagraph (CPI-C) is designed for high-contrast direct imaging of exoplanets, with an inner working angle of 0.35 arcseconds at visible wavelengths. It is intended to follow up planets identified through radial velocity observations and to study planetary formation, evolution, and protoplanetary disks. The instrument operates over wavelengths of 0.53–1.6 μm and includes seven broad-band filters.

High-sensitivity terahertz detection module The high sensitivity terahertz detection module (HSTDM) is designed for space-based observations of terahertz radiation, avoiding atmospheric absorption that limits ground-based observations. It is a high-resolution spectrometer and the first planned spaceborne heterodyne receiver to use a niobium nitride-based superconducting tunnel junction mixer.

See also Hubble Space Telescope – NASA/ESA space telescope launched in 1990 James Webb Space Telescope – NASA/ESA/CSA space telescope launched in 2021 Nancy Grace Roman Space Telescope – NASA infrared space telescope Euclid (space telescope) – European visible and near-infrared space observatory, launched in 2023 Lists of telescopes

Notes

References

Illustrations

Worked examples

Example 1 — a first encounter with Xuntian

Start with the simplest possible case. Write down what Xuntian claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In astronomy, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Xuntian before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Xuntian ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Xuntian

In research: Xuntian appears in astronomy research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Xuntian in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Xuntian is common in secondary-school and first-year university syllabi. It links to neighbouring topics 2027 in China, 2027 in spaceflight, Components of the Tiangong space station, so understanding it makes those chapters shorter.
In everyday life: Look for Xuntian outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Xuntian in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Xuntian means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Xuntian out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Xuntian in simple terms?

Why does Xuntian matter?

Because it connects several astronomy ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Xuntian?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Xuntian.