Proxima Centauri
In 1915, Robert Innes stood at the Union Observatory in Johannesburg and spotted a faint star moving across the sky. This star shared the same proper motion as Alpha Centauri, suggesting they were neighbors. Innes named it Proxima Centauri to mark its status as the nearest known star to our Sun. The discovery paper appeared that year, but confirmation took time. Joan Voûte measured its trigonometric parallax in 1917 from the Royal Observatory at the Cape of Good Hope. Harold L. Alden confirmed the distance again in 1928 with a more precise measurement. These early studies established that Proxima Centauri was not just another distant point of light. It was a neighbor, sitting only 4.25 light-years away. Its apparent magnitude of 11.13 meant no human eye could see it without aid. Even from Alpha Centauri A or B, this star would appear as a fifth magnitude object. The International Astronomical Union officially approved the name Proxima Centauri on the 21st of August 2016. Before that, it had been known by various designations including Alpha Centauri C.
Proxima Centauri holds about 12.5% of the Sun's mass and has an average density thirty-three times greater than ours. Its diameter measures roughly one-seventh that of the Sun, yet it packs immense gravitational force. Surface gravity reaches 162 times Earth's value, recorded as log g = 5.20. Convection moves energy through its entire interior instead of radiating outward like our own star. This process circulates helium ash throughout the core rather than letting it accumulate. As a result, Proxima will burn nearly all its hydrogen before leaving the main sequence. It remains stable for approximately four trillion years. Magnetic fields form via convection and release energy in sudden flares. On the 6th of May 2019, a flare event reached temperatures up to 27 million Kelvin. These bursts emit X-rays comparable to those from the much larger Sun. About 88% of the surface may be active at any given time. The chromosphere shows strong emission lines of singly ionized magnesium at 280 nanometers. Even during quiet periods, corona temperature stays near 3.5 million Kelvin. A weak stellar wind carries no more than 20% of the solar wind’s mass loss rate.
Three planets orbit Proxima Centauri: two confirmed and one candidate. Proxima Centauri b circles the star every 11.2 Earth days at roughly 0.05 astronomical units. Its mass is at least 1.07 times that of Earth. Scientists first detected hints of this planet in 2013 using archival data from Mikko Tuomi. Guillem Anglada-Escudé led a team of thirty-one astronomers who announced confirmation on the 24th of August 2016. They used HARPS and UVES spectrographs located at La Silla and Paranal observatories. Proxima Centauri d orbits closer still, completing a lap every 5.15 days with a minimum mass of 0.29 Earths. This sub-Earth was independently confirmed by NIRPS spectrograph work published in July 2025. A third body, Proxima Centauri c, remains disputed. Mario Damasso reported it in April 2019 as a possible super-Earth or gas dwarf. Hubble astrometry supported its existence in 2020, but other teams found no clear detection. Some researchers suggest rings around the object could explain brightness anomalies. The habitable zone lies between 0.3 and 0.4 AU from the star. Any planet there would likely be tidally locked, showing one side perpetually to the red glow.
Early measurements began with John Stanley Plaskett’s interferometry estimate in 1925. He calculated the diameter as 207,000 miles. Harlow Shapley identified flare activity in 1951 after reviewing photographic records. About 8% of images showed measurable increases in magnitude. The Einstein Observatory produced detailed X-ray curves of flares in 1980. Later satellites like EXOSAT, ROSAT, ASCA, XMM-Newton, and Chandra continued monitoring. In 2016, a superflare increased optical brightness by a factor of 68 times. Similar events occur five times yearly but last only minutes. New Horizons captured images of Proxima Centauri on the 22nd of April 23, 2020. These revealed large parallax effects when compared to Earth-based views. Gaia Data Release 3 published updated parallax values in 2020. Previous estimates came from Hipparcos Catalogue (1997), Hipparcos New Reduction (2007), and Hubble fine guidance sensors (1999). Current distance stands at 4.25 light-years based on these refined calculations. Observations remain limited to southern latitudes below 27° north due to declination constraints.
Voyager 1 would take over seventy-three thousand years to reach Proxima Centauri if traveling directly toward it. Nuclear pulse propulsion projects such as Orion, Daedalus, and Longshot offered century-scale travel concepts decades ago. Breakthrough Starshot proposes microprobes moving at twenty percent the speed of light. Lasers totaling one hundred gigawatts power these tiny craft. They could arrive within two decades after launch or enter orbit after roughly fourteen decades using swing-bys. Information collected takes 4.25 years to return to Earth. Non-nuclear conventional engines require thousands of years for transit. Galactic motion means slow probes must catch the star during its closest approach window. That window opens around 26,700 years from now when proximity reaches approximately 3.11 light-years. After that point, Proxima will recede beyond easy reach. The Alpha Centauri system may lose binding in about 3.5 billion years. Until then, interstellar missions face immense technical hurdles despite the short cosmic distance.
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Common questions
When was Proxima Centauri discovered and by whom?
Robert Innes discovered Proxima Centauri in 1915 while working at the Union Observatory in Johannesburg. He identified it as a faint star sharing proper motion with Alpha Centauri, leading to its naming as the nearest known star to our Sun.
What are the physical characteristics of Proxima Centauri compared to the Sun?
Proxima Centauri holds about 12.5% of the Sun's mass and has an average density thirty-three times greater than ours. Its diameter measures roughly one-seventh that of the Sun yet generates surface gravity reaching 162 times Earth's value.
How many planets orbit Proxima Centauri and when were they confirmed?
Three planets orbit Proxima Centauri including two confirmed bodies and one candidate object. Scientists announced confirmation of Proxima Centauri b on the 24th of August 2016 while independent work published in July 2025 verified the sub-Earth Proxima Centauri d.
Where is Proxima Centauri located relative to Earth and how far away is it?
Proxima Centauri sits only 4.25 light-years away from Earth making it the closest known star to our Solar System. Observations remain limited to southern latitudes below 27° north due to declination constraints.
When will Proxima Centauri be closest to Earth during its galactic motion?
The proximity window opens around 26,700 years from now when distance reaches approximately 3.11 light-years. After that point Proxima Centauri will recede beyond easy reach as part of the Alpha Centauri system.