You're asking for evidence that the Sun's corona is hotter than its photosphere. Here's how we know:

* Spectroscopic Observations: Scientists use spectrometers to analyze the light emitted from different layers of the Sun. The corona emits a unique spectrum of light that indicates extremely high temperatures, much hotter than the light emitted from the photosphere.

Here's why this is significant:

* The Temperature Paradox: The Sun's corona, the outermost layer, should logically be cooler than the photosphere, the visible surface. However, the opposite is true. This is a long-standing mystery in solar physics, and scientists are still working to fully understand the mechanisms responsible for heating the corona to such extreme temperatures.

Let me know if you'd like more details on the spectroscopic evidence or the reasons behind the temperature paradox!