Overview

Pollux is the most luminous star in the constellation Gemini as seen from Earth. Its orange hue marks it as an evolved giant rather than a hot main-sequence star. Located at a relatively close interstellar distance, Pollux is prominent in northern-hemisphere skies and has been recognized since antiquity by multiple cultures.

Physical characteristics

Classified as a K-type giant (K0 III in many catalogues), Pollux has left the main sequence after exhausting hydrogen at its core. As a result it has expanded and cooled compared with its earlier life as a hotter, A-type star. Its diameter is often stated to be on the order of several million kilometres; measurements place the star's diameter at roughly 11,000,000 kilometres, many times larger than the Sun's (diameter estimates). Its apparent brightness and color are typical of a mid-K giant.

Evolution and history

Pollux began life as a more massive, hotter star and spent much of that time on the main sequence fusing hydrogen. As core hydrogen ran out it expanded into a giant, developing a cooler outer envelope and brighter total luminosity. This evolutionary path is typical for stars of a few solar masses and explains Pollux's present spectral type and radius.

Planetary system and scientific importance

Observers have detected at least one companion around Pollux: a long-period, gas-giant exoplanet discovered through radial-velocity monitoring. The presence of a planet orbiting a giant star offers useful data on the survival and evolution of planetary systems as their host stars age. Pollux thus serves as an accessible laboratory for stellar and exoplanet studies.

Notable facts and quick reference

  • Constellation: Gemini
  • Spectral type: K-type giant
  • Size: diameter ≈ 11,000,000 km (several times the Sun's)
  • Companion: at least one confirmed exoplanet detected by radial-velocity

Because of its brightness and proximity, Pollux remains a frequent subject of photometric and spectroscopic observation. It illustrates key stages of stellar aging and the influence those stages can have on surrounding planetary bodies.