How are stars primarily classified?

Stars are primarily classified by their temperature, which is a key factor affecting their color, luminosity, and spectral characteristics. The classification system most commonly used is the Harvard classification system that categorizes stars into spectral types based on their surface temperatures. This classification ranges from hot, blue O-type stars with temperatures above 30,000 Kelvin, to cool, red M-type stars with temperatures below 3,500 Kelvin.

The temperature of a star impacts not only its color but also other properties like brightness and lifespan. For example, more massive stars are typically hotter and may burn through their nuclear fuel more quickly than their cooler counterparts. Therefore, by classifying stars by temperature, astronomers can infer many other critical characteristics about a star, including its stage in the stellar lifecycle and potential for hosting planetary systems.

While size, age, and distance are also important in the context of star studies, they are secondary factors that can vary independently of temperature and do not serve as the primary classification criteria. Size can influence luminosity but isn't a direct classification metric, and age can be difficult to determine. Distance provides context for luminosity but does not categorize the star itself.