When we look at the Sun with our eyes, we see only a bright white disk. With images returned by the Solar Ultraviolet Imager (SUVI), the Sun appears in multiple forms across wavelengths that are invisible to us.

Mounted on the Fengyun-4C satellite, SUVI enables simultaneous observations of the Sun in four extreme ultraviolet wavelengths: 9.4 nm, 17.1 nm, 21.1 nm, and 30.4 nm.

What are we actually seeing?

These images are not simple filtered photos, but selections of plasma at different temperatures. Each wavelength is sensitive to plasma within a specific temperature range, corresponding to different regions of the solar atmosphere, such as the chromosphere, transition region, and corona. By combining these views, we can observe the Sun in a layered way, from cooler regions to extremely hot structures.

What do the four wavelengths represent?

🟢 9.4 nm — Very hot coronal plasma (~6 million K), mainly associated with solar flares and active regions.

🟡 17.1 nm — Cooler coronal plasma (~600,000 K), revealing coronal loop structures.

🟣 21.1 nm — Intermediate-temperature coronal plasma (~2 million K), highlighting active regions.

🔴 30.4 nm — Emission from the chromosphere and transition region (~50,000–80,000 K), dominated by helium emission and tracing the Sun’s lower atmosphere.

More than imaging — continuous monitoring

As a “space sentinel” aboard Fengyun-4C, SUVI continuously monitors the Sun’s chromosphere, transition region, and corona, capturing solar activity and eruptions in real time and transmitting the data back to Earth.

These observations support real-time solar monitoring, improve space weather forecasting, and help provide early warnings for satellites, navigation systems, and aviation communications.