FactSentinel

The Sun is a star, not a planet. Astronomers classify stars as massive, self-luminous spheres of plasma that generate energy through nuclear fusion in their cores. The Sun fuses roughly 600 million tons of hydrogen into helium every second, releasing the light and heat that sustain life on Earth. Planets, by contrast, do not produce their own energy through fusion. They shine only by reflecting light from a star, and they are far smaller and less massive than the stars they orbit.

The scale difference alone makes the distinction clear. The Sun contains about 99.86 percent of all the mass in the solar system, and its diameter is roughly 109 times that of Earth. Under the International Astronomical Union's 2006 definition, a planet must orbit a star, be massive enough to assume a nearly round shape, and have cleared its orbital neighborhood of other debris. The Sun fails the first requirement because it does not orbit another star. Instead, the planets, asteroids, and comets of the solar system orbit it. The Sun itself orbits the center of the Milky Way galaxy.

The confusion may stem from the fact that the Sun is sometimes described as a celestial body or a heavenly object, or from ancient astronomy, which used the word "planet" for any wandering light in the sky, including the Sun and Moon. That older usage reflected limited knowledge of how these objects work. Modern astronomy classifies the Sun as a G-type main-sequence star, often called a yellow dwarf, and it is about 4.6 billion years old.