Why are some stars bright and others dim

What is a star?A star is any massive self-luminous celestial body of gas that shines by radiation derived from its internal energy sources. Of the tens of billion. . How is a star’s brightness measured?Astronomers define stellar brightness in terms of magnitudes: the apparent magnitude (the perceived and measured brightness of a star) and the abso. . Why do stars tend to form in groups?Stars tend to form in groups because of where star formation occurs. Stars form within a molecular cloud, where protostars begin to take shape in a. . Why do stars evolve?Stellar evolution occurs when a star loses its energy from continuous nuclear fusion reactions, causing instability due to decreasing gas pressure. . [pdf]
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