Across the night sky, stars are organized into patterns called constellations, which have served as tools for navigation and storytelling throughout human history. While they may look like similar pinpricks of light to the naked eye, stars vary wildly in color, size, and temperature; blue stars are among the hottest, while red stars are relatively cooler. Astronomers use the Hertzsprung-Russell diagram to classify these stars and study their evolution. Together, hundreds of billions of these diverse stars congregate to form galaxies, which are the fundamental building blocks of the observable universe.
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