Friday, June 29, 2007

Alpha Centauri ABC

Star type
g Alpha Centauri C: M5.5Ve (main sequence red dwarf)
g Alpha Centauri A: G2 V (yellow)
g Alpha Centauri B: K0-1 V (reddish-orange dwarf)

Distance from Earth
g C: 4.223 ly
g A: 4.395 ly; To reach from Earth in 20 years, ship must average 0.21c; a one-way trip to Alpha Centauri would take, assuming a constant acceleration of 1g up to a high relativistic speed during the first half of the flight and a constant deceleration of 1g during the second half, only 3 years spaceship time, while 6 years will have passed outside the spaceship
g B: 4.395 ly

Star Service No.
g MW2

g C: 5 by-6 by, possibly 1 by
g A: 4.68 by; 6.8 by-7.6 by (if no convective core)
g B: 5.8 by

g C: 14.5%; 12.3%; 2700 K
g A: 123%; 109%-110%; 5800 K
g B: 86.5%; 90.7%; 5300 K

Brightness (xSol)
g C: 19,000 times fainter than the Sun (disk barely visible at 1AU), flare star
g A: 152% to 160%
g B: 45% to 52%

g C: 10%
g A: NA
g B: NA

Comparison to Sol
g See illustration

Picture of star
g C: See picture
g A: See picture

Star system features
g Alpha Centauri A and B form a close binary separated on average by only about 23.7 AUs of an orbital semi-major axis (which is only slightly greater than the distance between Uranus and the Sun); the star swings between 11.4 and 36 AUs away in a highly elliptical orbit (e= 0.519) that takes 79.9 years to complete; Alpha Centauri C is located about 13,000 AUs fromA and B and takes 500,000 years to orbit that pair in hyperbolic orbit). Any planets within 2 AU of either Star A or Star B can retain a stable orbit.

Known planets
g C: Potentially a 0.8 Jupiter mass with an orbital period of between 1-2.7 years
g A: None found
g B: A small rocky world, which likely has a lava-like consistency, orbits 4 million miles (6.4 million kilometers) from star — much closer to its star than Mercury is to our sun — making its year only 3.2 days long. Planet has a mass of slightly more than Earth's. The world would be way too hot to support Earth-liked life.

Habitable zone
g C: 0.02 to 0.06 AU (orbital period of 2-16 days; tidally locked to a flare star). Probably too small of a star to host a habitable planet unless that planet has a stabilizing moon. Probability of a habitable planet is 1.07%.
g A: 1.2-1.3 AUs (midway between the orbits of Earth and Mars; 1.34 year orbit; as viewed from a hypothetical planet around either star, Alpha Centauri B’s brightness increases as the two approach and decreases as they receded; the variation in brightness is considered to be insignificant for life onEarth-type planets around either star; under optimal conditions, either Alpha Centauri A and B could hold four inner rocky planets at same distances as in Solar System; AB system may be 1.3 to 2.3 times as enriched in elements heavier than hydrogen than our Solar System; either A or B could have one or two “rocky” planets in orbital zones where liquid water is possible; B star would provide more light than the full Moon does on Earth as its brightest night sky object). Probability of a habitable planet is 5.4%.
g B: 0.73 to 0.74 AU (just beyond orbit of Venus; orbital period just less than an Earth year, however). Probability of a habitable planet is 5.7%.

Orbital map
g See map

View from star
If our own Sun, Sol, were viewed from the Alpha Centauri system, it would be located in Cassiopeia near the border with Perseus and about degrees north of a double cluster near the nebula IC 1805/1848, visible as a bright yellow star that would be almost as bright as Capella (Alpha Aurigae) appears in Earth's night sky
g C: The sky around faint Proxima Centauri is dominated by two stars: the yellow and orange dwarf stars that lie at the heart of the Alpha Centauri system. Just a fifth of a light year distant, they shine with a magnitude approaching -7, far brighter than Venus ever appears from Earth. See sky map.
g A: SAA; Seen from Alpha Centauri A or B, Proxima would be a 4.5 magnitude star.
g B: SAA

Nearby stars
(Star systems with 10 light years)
g Sol: 4.4 ly
g Barnard’s Star: 6.5 ly
g Ross 154: 8.1 ly
g Wolf 359: 8.3 ly

Map locating star system
g See stellar map

Location in Earth sky
Southeastern corner of Constellation Centaurus (cannot be viewed from middle northern latitudes of around 40 degrees)
g A: Not visible with naked eye

Other names
g C: Proxima Centauri, V645 Centauri, Gl 551, Hip 70890, LHS 49
g A: Rigil Kentaurus, Alp Cen A, Alf Cen A, HR 5459, Gl 559 A, Hip 71683, HD 128620, CP(D)-60 5483, SAO 252838, FK5 538, LHS 50
g B: Alp Cen B, Alf Cen B, HR 5460, Gliese 559 B, Hip 71681, HD 128621, LHS 51

Sci-fi mentions
g Episodes “Metamorphosis” and “Tomorrow is Yesterday” in “Star Trek: The Original Series”
g “Lost in Space”
g Robert Silverberg’s “Revolt on Alpha C”
g Leigh Brackett’s “Alpha Centauri — Or Die!”
g Mary Russell’s “The Sparrow”
g A.E. van Vogt’s “Far Centaurus”
g Charles Pelligrino’s “Flying to Vahalla”
g Planet Ecaz was Alpha Centauri B in “Dune”
g Wunderland is Alpha Centauri A in Larry Niven’s “Known Space” series
g Alpha Centauri A is home to planet Cassida, and Alpha Centauri B to Newton in Gordon R. Dickson's “Childe Cycle” (more commonly known as the "Dorsai series")
g Proxima is Alpha Centauri A in Robert Heinlein’s “Friday”
g Planet Tiber orbits Alpha Centauri A in Buzz Aldrin & John Barnes’ “Encounter with Tiber”
g Alpha (aka New Earth) orbits Alpha Centauri A in Isaac Asimov’s “Foundation” series
g Robotic probe is sent there in Jack McDevitt's short story "Windows"
g Among the first 26 interstellar expeditions is one to each of the stars in this trinary in Frederick Pohl's short story "Father of the Stars"
g Centauri system is destination of the Skipstone in Barry N. Malzberg and Bill Pronzini’s “Inaugural”
g Alpha and Beta are mentioned in Poul Anderson’s “Starfarers”; first robot spacecraft departs for it in about 10 years after publication of a theory about to practically travel near the speed of light
g Mentioned in "Star Trek: The Next Generation" episode "Elementary, Dear Data"
g Troxxt set up a base on a planet orbiting Proxima Centauri in William Tenn's short story "The Liberation of Earth"
g Ship "The Traveler" was intended to carry a load of colonists to Alpha Centauri in Poul Anderson's "Gypsy"
g Inhabited moon Pandora orbits the fictional gas giant Polyphemus in the Alpha Centauri system in science fiction movie "Avatar"
g The Garnishee inhabit the planet Dormite, which orbits the binary pair Lapha and Promixa Centauri in Harry Harrison's "Star Smashers of the Galaxy Rangers".
g A habitable planet orbiting Rigel Centaurus (Star A or Proxima Centauri) climatically is a cold world in Alfred Bester's short story "Fondly Fahrenheit".
g Character visits "Alpha Centauri IV" as a high school graduation present in Robert Silverberg's novel "The Man in the Maze". In same book, colonists live on Star B's sixth planet and Star B's eighth planet is a gas giant with a low density core and gravity only slightly greater than Earth's.
g Planet Hellespont orbits one of the system's stars in Chris Berman's novel "Ace of Aces"
g Mentioned in Vylar Kaftan's short story "I'm Alive, I Love You, I'll See You in Reno."

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