1. Temperature: This is the most fundamental property that determines a star's color, spectral type, and energy output. Stars are classified into spectral types (O, B, A, F, G, K, M) based on their temperature, with O stars being the hottest and M stars the coolest.
2. Luminosity: This refers to the total amount of energy a star radiates per second. Luminosity is closely related to a star's mass, with more massive stars being significantly more luminous.
These two properties are often plotted together on a Hertzsprung-Russell diagram, which provides a valuable tool for understanding the evolution of stars.
