Capella

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Capella-Sun comparison

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Capella (Latin for "little goat", symbolized as α Aurigae, or Alpha Aurigae) is the brightest star in the constellation of Auriga, the sixth-brightest in the night sky, and the third-brightest in the northern celestial hemisphere after Arcturus and Vega. A prominent star in the winter skies of the northern hemisphere, Capella is actually a quadruple star system 42.9 light-years from the Sun. It consists of two binary pairs: the first pair, Capella Aa and Capella Ab, are two bright giant stars in a close orbit, while the second pair, Capella H and Capella L, are fainter, distant, and smaller red dwarfs.

Overview

Capella Aa and Capella Ab are both G-type giants, though Aa is slightly larger and brighter than its companion. The primary, Capella Aa, has exhausted its core hydrogen and has expanded and cooled to become a red giant, though it is now in a later evolutionary stage where it is considered a yellow giant. Capella Ab, while slightly smaller, is also in a similar stage of evolution. The two giants are locked in a tight orbit around each other, completing a cycle approximately every 104 days.

The secondary pair, Capella H and Capella L, orbit at a great distance from the primary pair, taking over 400 years to complete a single orbit. These stars are much less massive and luminous than their giant counterparts, showcasing the diversity of stellar evolution within this complex system.

Observation

Capella is easily visible to the naked eye, appearing as a single point of light. Through a telescope, its binary nature was first discovered in 1899 by professor William Wallace Campbell of the Lick Observatory. The discovery of the secondary pair, Capella H and Capella L, came later through more advanced observational techniques.

Capella plays a significant role in various cultural and mythological traditions. In Inuit astronomy, it is known as the "Goat Star" and is featured prominently in winter sky stories. Its Latin name, "little goat", is believed to originate from its representation in the constellation Auriga, where it is depicted as a goat being carried by the charioteer.

Scientific Significance

The Capella system has been the subject of extensive study due to its proximity and the rare opportunity it provides to study the dynamics of a quadruple star system. Observations and models of Capella's complex gravitational interactions have contributed significantly to our understanding of stellar evolution, particularly in the late stages of giant stars.

See Also

• Binary star
• Giant star
• Stellar evolution
• Constellation