Proxima Centauri

Proxima Centrauri
Observation data
Epoch J2000
Constellation Centaurus
Right ascension 14h 29m 43.0s
Declination -62° 40' 46"
Apparent magnitude (V) 11.05
Spectral type M5.5 V
B-V color index 1.90
U-B color index 1.49
Variable type Flare star
Astrometry <tr valign=top><td>Radial velocity (Rv)</td><td>-20.3 km/s</td></tr><tr valign=top><td>Proper motion (μ)</td><td> RA: -3775.64 mas/yr
Dec.: 768.16 mas/yr </td></tr><tr valign=top><td>Parallax (π)</td><td>771.99 ± 2.25 mas</td></tr><tr valign=top><td>Distance</td><td>Expression error: Unrecognised punctuation character "[". ± Expression error: Unrecognised punctuation character "[". ly
(Expression error: Unrecognised punctuation character "[". ± Expression error: Unrecognised punctuation character "[". pc)</td></tr><tr valign=top><td>Absolute magnitude (MV)</td><td>15.49</td></tr>
Mass 0.12 M
Radius 0.15 R
Luminosity 5-12 × 10-5 L
Temperature 2,670 K
Metallicity 10%
Rotation 30-33 days
Age estimated 1 × 109 years
Other designations
α Centauri C, V645 Centauri, GCTP 3278.00, GJ 551, LHS 49, LFT 1110, LTT 5721, HIP 70890.

The red dwarf star Proxima Centauri, part of the Alpha Centauri star system, is the nearest star to our Sun, 4.22 light years away. As the name suggests, it is located in the constellation of Centaurus. Proxima Centauri was discovered to share the same proper motion as Alpha Centauri in 1915 by Robert Innes while he was Director of the Union Observatory in Johannesburg, South Africa. It was Innes who suggested the name Proxima. In 1917 at the Royal Observatory, Cape of Good Hope, the Dutch astronomer J. Voûte measured the trigonometric parallax and determined that Proxima was indeed at the same distance as Alpha Centauri, and hence was also the faintest star known at the time[1].


Red dwarfs in general are far too faint to be observable with the naked eye, and Proxima Centauri is no exception. It has an apparent magnitude of 11 while its absolute magnitude is a very dim 15.5. Seen from Alpha Centauri A or B, Proxima would be a 4.5 magnitude star.

Based on the parallax of 772.3 ± 2.4 milliarcseconds measured by Hipparcos (and the more precise parallax determined using the Fine Guidance Sensors on the Hubble Space Telescope of 768.7 ± 0.3 milliarcseconds), Proxima Centauri is roughly 4.2 light years from Earth, or 270,000 times more distant than the Sun. Its closest neighbors are Alpha Centauri A and B (at 0.21 light years), the Sun, and Barnard's Star (at 6.55 light years). From Earth's vantage point, Proxima is separated by 2° from Alpha Centauri, or 4 times the angular diameter of the full Moon.

At least among the known stars, Proxima Centauri has been the closest star to the Sun for about the last 32,000 years and will be so for about another 33,000 years, when it will be replaced by Ross 248[2].

In 2002, VLTI used optical interferometry to measure an angular diameter of 1.02 ± 0.08 milliarcsec for Proxima Centauri. Knowing its distance, the actual diameter can be determined to be about 1/7 that of the Sun, or 1.5 times that of Jupiter. Its mass is also about 1/7 that of the Sun, or 150 times that of Jupiter.

At a distance to Alpha Centauri of just 1/20th of Proxima Centauri's distance to the Sun, Proxima may actually be in orbit about Alpha, with an orbital period on the order of 500,000 years or more. For this reason, Proxima is sometimes referred to as Alpha Centauri C. However, it is possible that it may not actually be in orbit, although the association is unlikely to be entirely accidental as it shares approximately the same motion through space as the larger star system[3].

Proxima, along with Alpha Centauri A and B, are among the "Tier 1" target stars for NASA's Space Interferometry Mission (SIM). SIM will be able to detect planets as small as three Earth-masses within two Astronomical Units of a "Tier 1" target. Due to Proxima's small mass and distance, SIM would be able to detect even smaller planets around this star, should they exist.

Traveling to Proxima Centauri

Proxima Centauri has been suggested as a logical first destination for interstellar travel, although as a flare star it would not be particularly hospitable. The current standard spaceship, the Space Shuttle, travels in orbit at 7.8 km/s. At that speed, it would take 160,000 years to reach Proxima. The fastest man-made spacecraft, the Helios II deep space probe, has set a speed record of 70.2 km/s. Even at that speed, the journey to Proxima Centauri would take 18,000 years. The proposed VASIMR propulsion system, possibly able to achieve speeds up to 300 km/s, would shorten the journey to a "mere" 4,200 years —still firmly beyond the current lifespan of both man and machine. It follows that interstellar travel would require significant development of radical ideas to become feasible, such as hypothetical generation ships, laser-pushed solar sails, nuclear fusion powered Bussard ramjets, nuclear pulse drives or warp drives.

See also


  1. J Voûte, A 13th magnitude star in Centaurus with the same parallax as α Centauri, Monthly Notices of the Royal Astronomical Society, Vol. 77 (June 1917), pp. 650-651; fulltext
  2. R Matthews, The Close Approach of Stars in the Solar Neighbourhood, Royal Astronomical Society Quarterly Journal Vol. 35 (1994), p. 1-9; fulltext
  3. R Matthews, G Gilmore, Is Proxima really in orbit around α Cen A/B?, Monthly Notices of the Royal Astronomical Society, Vol. 261, L5-L7 (1993); fulltext

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