Which observable characteristic helps classify a star’s temperature?

The observable characteristic that helps classify a star's temperature is its color. The color of a star is a direct result of its surface temperature, with hotter stars emitting light that appears blue or white, while cooler stars tend to emit light that appears red or orange. This relationship is rooted in the principles of blackbody radiation, where the peak wavelength of light emitted by a star shifts depending on its temperature, which aligns with Wien's displacement law.

For example, a star with a temperature of around 10,000 Kelvin may emit light that appears blue, whereas a star cooler than about 3,000 Kelvin would appear red. This color classification helps astronomers determine the star's temperature without needing to measure it directly, making it a vital tool in stellar classification and understanding the lifecycle of stars.

Brightness, the speed of rotation, and the size of a star's orbit do not provide as direct a measure of temperature as color does. Brightness can be influenced by various factors, such as distance from Earth and intrinsic luminosity. The speed of a star's rotation can affect its shape and surface conditions but is not directly related to its temperature. Similarly, the size of its orbit pertains to the star's position and gravitational influences rather than its thermal characteristics