What if the conditions change drastically?
- Strong omni-present magnetic fields
- Fast rotation
- Global cells (so that surface curvatures matters)
- Very efficient radiation (A-type dwarfs to early M-type supergiants)
- Inefficent radiation (metal-poor stars, M-type dwarfs, brown dwarfs)
- Complex chemistry (molecules, dust)
- Stellar wind
- Strong pulsations
We need a few calibration points very different from solar conditions.