Star Characteristics and Classification

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Giant

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A highly luminous, exceptionally massive star. Forms when a main sequence star runs out of hydrogen, causing the core to shrink and burn helium. Outer layers may expand, causing the star to glow red, known as red giants.

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H-R Diagram

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A graphical plot showing the relationship between a star’s luminosity and its surface temperature. Used to classify stars and show how stars change over time.

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Luminosity

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The brightness of an object that gives off light, such as a star. Determined by comparing a star’s apparent brightness with its distance from Earth.

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Main Sequence

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A star in a stable, middle stage of its development. Over 90% of stars in the universe are main sequence stars, including the Sun.

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Star

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A celestial body composed of hot gases that radiate energy, including light and heat. Energy comes from nuclear fusion, where hydrogen atoms join to form helium.

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Supergiant

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A very bright star that is usually larger and more massive than a giant star.

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White Dwarf

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A small, dense, faint star. Forms near the end of a star’s life cycle when the outer layers of a giant are shed, leaving a dense oxygen-carbon core.