Spectral class A refers to a category of stars characterized by their strong hydrogen lines and relatively high temperatures, typically ranging from 7,500 to 10,000 Kelvin. These stars emit a bright white or bluish light and are often more massive than the Sun, with a lifespan of about 1 to 2 billion years. Stars in this class are known for their distinct spectral features, which are used by astronomers to classify them. Examples of A-type stars include Sirius A and Altair, both of which are prominent in the night sky and serve as important reference points for studying stellar evolution.