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In 1968 Shirley Chisholm became the first Black woman elected to the United States Congress. In 1972 she launched a campaign for the Democratic presidential nomination, breaking another political barrier.
MORE →Reflects the personal views, recollections, and perspective of the author, Mike Davis.
This is a personal recollection on the Move fire on May 13, 1985
 Orbits of Proxima d, Proxima b and Proxima c around Proxima Centauri | |
| Discovery[1] | |
|---|---|
| Discovered by | Damasso et al. |
| Discovery site | HARPS |
| Discovery date | January 2020 |
| Radial velocity | |
| Orbital characteristics | |
| 1.489±0.049 AU[2] | |
| Eccentricity | 0.04±0.01[3] |
| 1928±20 d[3] | |
| Inclination | 133±1[3] |
| 331±1[3] | |
| −4±4[3] | |
| 2456202±21[3] | |
| Semi-amplitude | 1.1±0.2[3] |
| Star | Proxima Centauri |
| Physical characteristics | |
| Mass | 7±1 M🜨[3] |
| Temperature | 39 K (−234.2 °C; −389.5 °F)[1] |
Proxima Centauri c (also called Proxima c[2] or Alpha Centauri Cc) is a disputed exoplanet candidate, proposed to be orbiting the red dwarf star Proxima Centauri, which is the closest star to the Sun and part of a triple star system. It is located approximately 4.2 light-years (1.3 parsecs; 40 trillion kilometres; 25 trillion miles) from Earth in the constellation of Centaurus. If Proxima c exists, this would make it, along with Proxima b and Proxima d, the closest known exoplanets to the Solar System.
As originally proposed, Proxima Centauri c would be a super-Earth or mini-Neptune about 7 times as massive as Earth,[a] orbiting at roughly 1.49 AU (223 million km; 139 million mi) every 1,928 days (5.28 years).[3] Due to its large mass and its distance from Proxima Centauri, the exoplanet would be uninhabitable and too cold for liquid water to exist on the surface, with an equilibrium temperature of approximately 39 K (−234.2 °C; −389.5 °F).[1][4] According to a 2025 study, the originally proposed planet most likely does not exist, but there may be a smaller planet with a similar orbit.[5]
The planet does not transit its parent star from the point of view of an Earth-based observer.[6]
The planet candidate was first reported by Italian astrophysicist Mario Damasso and his colleagues in April 2019. Damasso's team had noticed minor movements of Proxima Centauri in the radial velocity data from the European Southern Observatory (ESO) HARPS instrument, analyzed earlier by Ukrainian astrophysicist Yakiv Pavlenko and his colleagues at the Instituto de Astrofísica de Canarias,[7][8][9] indicating a possible second planet orbiting Proxima Centauri.[10] The discovery was published on 15 January 2020.[1]
Subsequent studies in 2020 also found evidence for Proxima c via astrometry,[2] including Hubble data from c. 1995, allowing its inclination and true mass to be determined.[3] Also in June 2020, a possible directly imaged counterpart of Proxima c was detected in the infrared with SPHERE, but the authors admit that they "did not obtain a clear detection".[11] If their candidate source is in fact Proxima Centauri c, it is too bright for a planet of its mass and age, implying that the planet may have a ring system with a radius of around 5 RJ.[11] At the time, the multiple lines of evidence appeared to confirm the planet.[12]
However, a 2022 study questioned the planetary nature of the observed radial velocity signal corresponding to Proxima c, whose detection could not be recreated, attributing it to systematic effects.[13] As of 2025[update], evidence for Proxima c remains inconclusive; observations with the NIRPS spectrograph were unable to confirm it, but found hints of a lower-amplitude signal, different from the originally proposed planet, with a similar period.[5] Another 2025 study, reanalyzing Hubble and Gaia astrometry, estimated a mass of 3.4+5.2
−3.4 M🜨 for Proxima c, assuming a circular, face-on orbit. This is broadly consistent with previous estimates, but also consistent with a non-detection.[14]
Автори використали наші результати, отримані у співпраці з групою вчених з Інституту астрофізики на Канарських о-вах, для того, щоб відкинути можливість пояснення довгоперіодичної варіації параметрів спектру Проксими явищами зоряної активності.
The Alpha Centauri system | ||
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Source: Wikipedia. Article content is retrieved live through the MediaWiki API.
Proxima Centauri c (also called Proxima c or Alpha Centauri Cc) is a disputed exoplanet candidate, proposed to be orbiting the red dwarf star Proxima Centauri, which is the closest star to the Sun and part of a triple star system. It is located approximately 4.2 light-years (1.3 parsecs; 40 trillion kilometres; 25 trillion miles) from Earth in the constellation of Centaurus. If Proxima c exists, this would make it, along with Proxima b and Proxima d, the closest known exoplanets to the Solar System.
Proxima Centauri is the nearest star to Earth after the Sun, located 4.25 light-years (1.3 parsecs) away in the southern constellation of Centaurus. Discovered in 1915 by Robert Innes, it is a small, low-mass star, too faint to be seen with the naked eye, with an apparent magnitude of 11.13. Proxima Centauri is a member of the Alpha Centauri star system, being identified as component Alpha Centauri C, and is 2.18° southwest of the Alpha Centauri AB pair. It is currently 12,950 AU (0.2 ly) from AB, which it orbits with a period of about 550,000 years. Its Latin name means the 'nearest [star] of Centaurus'. Proxima Centauri is a red dwarf star with a mass about 12.5% of the Sun's mass (M☉), and average density about 33 times that of the Sun. Because of Proxima Centauri's proximity to Earth, its angular diameter can be measured directly. Its actual diameter is about one-seventh (15%) the diameter of the Sun. Although it has a very low average luminosity, Proxima Centauri is a flare star that randomly undergoes dramatic increases in brightness because of magnetic activity. The star's magnetic field is created by convection throughout the stellar body, and the resulting flare activity generates a total X-ray emission similar to that produced by the Sun. The internal mixing of its fuel by convection through its core and Proxima's relatively low energy-production rate, mean that it will be a main-sequence star for another four trillion years. Proxima Centauri has two known exoplanets and one candidate exoplanet: Proxima Centauri b, Proxima Centauri d and the disputed Proxima Centauri c. Proxima Centauri b orbits the star at a distance of roughly 0.05 AU (7.5 million km) with an orbital period of approximately 11.2 Earth days. Its estimated mass is at least 1.06 times that of Earth. Proxima b orbits within Proxima Centauri's habitable zone—the range where temperatures are right for liquid water to exist on its surface—but, because Proxima Centauri is a red dwarf and a flare star, the planet's habitability is highly uncertain. A sub-Earth, Proxima Centauri d, roughly 0.028 AU (4.2 million km) away, orbits it every 5.1 days. A candidate sub-Neptune, Proxima Centauri c, roughly 1.5 AU (220 million km) away from Proxima Centauri, orbits it every 1,900 d (5.2 yr).
Proxima Centauri b, also referred to as Proxima b, or Alpha Centauri Cb, is an exoplanet orbiting within the habitable zone of the red dwarf star Proxima Centauri in the constellation Centaurus. The host star is the closest star to the Sun, at a distance of about 4.2 light-years (1.3 parsecs) from Earth, and is part of the larger triple star system Alpha Centauri. Proxima b and Proxima d, along with the currently disputed Proxima c, are the closest known exoplanets to the Solar System. Proxima Centauri b orbits its parent star at a distance of about 0.04848 AU (7.253 million km; 4.506 million mi) with an orbital period of approximately 11.2 Earth days. Its other properties are only poorly understood, but it is probably a terrestrial planet with a minimum mass of 1.06 M🜨 and a slightly larger radius than that of Earth. The planet orbits within the habitable zone of its parent star; but it is not known whether it has an atmosphere, which would impact the habitability probabilities. Proxima Centauri is a flare star with intense emission of electromagnetic radiation that could strip an atmosphere off the planet. Announced on 24 August 2016 by the European Southern Observatory (ESO), Proxima Centauri b was confirmed via several years of Doppler spectroscopy measurements of its parent star. The detection of Proxima Centauri b was a major discovery in planetology, and has drawn interest to the Alpha Centauri star system as a whole. As of 2023, Proxima Centauri b is believed to be the best-known exoplanet to the general public. The exoplanet's proximity to Earth offers an opportunity for robotic space exploration.
Alpha Centauri (α Centauri, α Cen, or Alpha Cen) is a star system in the southern constellation of Centaurus. It consists of three stars: Rigil Kentaurus (Alpha Centauri A), Toliman (Alpha Centauri B), and Proxima Centauri (Alpha Centauri C). Proxima Centauri is the closest star to the Sun at 4.2465 light-years (ly), which is 1.3020 parsecs (pc), while Alpha Centauri A and B are the nearest stars visible to the naked eye. Rigil Kentaurus and Toliman are Sun-like stars (class G and K, respectively) that together form the binary star system α Centauri AB. To the naked eye, these two main components appear to be a single star with an apparent magnitude of −0.27. It is the brightest star in the constellation and the third-brightest in the night sky, outshone by only Sirius and Canopus. α Centauri AB are the nearest binary stars to the Sun at a distance of 4.344 ly (1.33 pc). Rigil Kentaurus has 1.1 times the mass (M☉) and 1.5 times the luminosity of the Sun (L☉), while Toliman is smaller and cooler, at 0.9 M☉ and less than 0.5 L☉. The pair orbit around a common centre with an orbital period of 79 years. Their elliptical orbit is eccentric, so that the distance between A and B varies from 35.6 astronomical units (AU), or about the distance between Pluto and the Sun, to 11.2 AU, or about the distance between Saturn and the Sun. Proxima Centauri is a small faint red dwarf (class M). Though not visible to the naked eye, Proxima Centauri is the closest star to the Sun at a distance of 4.24 ly (1.30 pc), slightly closer than α Centauri AB. The distance between Proxima Centauri and α Centauri AB is about 13,000 AU (0.21 ly), equivalent to about 430 times the radius of Neptune's orbit. Proxima Centauri has two confirmed planets—Proxima b and Proxima d. The former is an Earth-sized planet in the habitable zone (though it is unlikely to be habitable) while the latter is a sub-Earth which orbits very closely to the star. A possible but disputed third planet, Proxima c, is a mini-Neptune 1.5 astronomical units away. Rigil Kentaurus may have a Saturn-mass planet (Alpha Centauri Ab) in the habitable zone, though it is not yet known with certainty to be planetary in nature. Toliman has no known planets; the only candidate planet, Alpha Centauri Bb, was disproven in 2015.
Before the 1921 destruction of Tulsa’s Greenwood District, Black residents had created a remarkable center of business and community life. The district included stores, professional offices, entertainment venues and homes owned by Black citizens. Understanding Greenwood means learning what was built—not only what was burned.
MORE →Madam C.J. Walker
