Proxima Centauri is the star closest to our Solar System, located approximately 4.24 light-years away in the constellation Centaurus. Discovered in 1915, this stellar neighbor serves as a prime subject for understanding the most common type of star in the Milky Way. Despite its extreme proximity, it remains completely invisible to the unaided human eye.
The Star’s True Color and Spectral Class
Proxima Centauri is a red dwarf. Its intrinsic color is a deep, reddish hue, a direct result of its low surface temperature. This star is classified by astronomers as a spectral type M5.5V, with the “M” indicating its temperature-driven color and the “V” signifying it is a main-sequence star.
The surface temperature of Proxima Centauri is only about 3,000 Kelvin, which is significantly cooler than the Sun’s temperature of roughly 5,778 Kelvin. The color of a star is determined by the peak wavelength of the light it emits, a relationship described by Wien’s law. Cooler stars emit most of their energy at longer, redder wavelengths on the electromagnetic spectrum, causing them to appear red.
The vast majority of the light emitted by this star falls outside the visible spectrum, mostly in the infrared range. Therefore, a hypothetical planet orbiting Proxima Centauri would be bathed in light that is much redder than the sunlight that illuminates Earth.
Why Proxima Centauri Appears Faint
Despite being the closest star to Earth, Proxima Centauri is far too faint to be seen without a telescope. This is due to its extremely low luminosity. Proxima Centauri produces only about 0.16% of the Sun’s total energy output across all wavelengths.
Its low temperature means it is also a small star, with a radius only about one-seventh that of the Sun. This combination results in a faint apparent magnitude of approximately 11.13, which is well below the threshold for human vision.
The star’s absolute visual magnitude is an extremely dim 15.6, confirming that it is intrinsically a low-light star. Proxima Centauri is a type of variable star known as a flare star, meaning it experiences sudden, dramatic increases in brightness due to magnetic activity. These flare events, however, are brief and do not make the star reliably visible to the naked eye.
Proxima Centauri’s Place in the Alpha Centauri System
Proxima Centauri is the third member of the Alpha Centauri system, a gravitationally bound triple-star arrangement. It orbits the other two stars, Alpha Centauri A and Alpha Centauri B, which together form a close binary pair. Proxima Centauri is separated from this binary pair by a large distance of about 0.2 light-years.
The star completes one full orbit around the combined center of mass of Alpha Centauri A and B over an immense period of approximately 550,000 years. This distant, long-period orbit confirms its membership in the system.
Proxima Centauri has garnered significant attention because it hosts at least two confirmed exoplanets, Proxima b and Proxima d. Proxima b is a “super-Earth” planet that orbits within the star’s habitable zone, where temperatures could theoretically allow for liquid water. However, the star’s frequent, intense flares of ultraviolet radiation pose a significant challenge to the habitability of any orbiting world. Its proximity makes it a prime target for future research and missions.