What physical property is fundamental for astronomers sorting stars into the O, B, A, F, G, K, M sequence?

Answer

Surface temperature

The way astronomers sort billions of stars fundamentally relies on surface temperature, which dictates the star's spectral characteristics.

What physical property is fundamental for astronomers sorting stars into the O, B, A, F, G, K, M sequence?
physicsclassificationastronomytemperaturestars