67,000 BC : α Centauri crosses the ecliptic and shines as a star of +0.42 magnitude star, which is as bright as the southern star Achernar / α Eridani Distance is 1.67pc. or 5.33 light years.
50,000 BC : α Centauri shines as a brightish star of +1.7 magnitude in the present day constellation of Ara. This would have been Distance is 1.67pc. or 5.33 light years.
30,000 BC : Proxima Centauri becomes the closest star to the Sun and succeeding the close binary and variable star(s) Gliese 65 AB or more commonly known the flare star UV Ceti, that today is in the constellation of Cetus. (Spectral Type M5.5) Proxima remains the closest star for the next 65,000 years. [In 2005 AD the distance is given as 2.683 parsecs (8.75 light-years) having visual magnitudes of +12.5 and +13.0, respectively.]
2300 BC : α Centauri is twice the apparent distance away from β Centauri as seen today. The Pointers, as such, do not exist in the ancient literature.
1000 BC : Magnitude of α Centauri is exactly 0.00.
185 A.D., 7th Dec. : α Centauri becomes rivalled by a new star observed by the Chinese. Thisremained visible to the naked eye for eight months before fading from view. Analysis by Hsi Tze-tsung (1955) ties down the date and likely position (L=282° and b=0°) though Lundmark in 1921 gives it high marks for being a true and reliable event. Clarke and Stephenson in the “Historical Supernova” (1977) conclude this was a supernova event. They also conclude the object may correspond to the infrared object RCW 86 (G315.4-2.3), which lies about halfway between the open cluster NGC 5866 and α Cen, or alternatively 2.3′S of α Cen itself.
1689 AD, December : Jesuit priest, Father Richard, discovers the duplicity of α Cen from Ponicherry, Southern India.
1752 AD : First meridian circle observations by explorer Lacaillé. He gives the rough estimates of the positions of the double star. It is clearly obvious that the system is in real connection by comparing Richard’s and other early telescopic observations. This is not realised until Sir William Herschel in 1801 and who states the possibility that stars can possibly exist as gravitationally attached binaries.
1826: James Dunlop measures the stellar positions as ΔRA 1.783 and ΔDec. as 18.788 (22.45″), translating into the position angle as 56° 49′ (212.66°). He also gives magnitudes as 1st and 4th, and oddly describes the colours of the two stars as strong reddish yellow.
1831 to 1834 : Thomas Henderson from the Cape of Good Hope makes the first parallax measurements using a mural circle finding an initial distance of 4.21y. These results, however, are not published due to doubt in the correctness of his measurements.
1834 : Sir John Herschel makes the first reliable micrometric observations of the pair and till 1996.417 others are made by other observers. He constructs an open-air observatory in Claremont, some six miles west of Capetown, installing his 0.45 metre (18-inch) 20-foot reflector. Due to the apparent changes since the observations by Lacaillé and others. Herschel starts conducting more frequent observations between 1834 and the beginning of 1838, hopefully to ascertain the orbital parameters and to improve the parallax measurements.
1838, December : Frederick Bessel publishes some parallax measurements prior to Henderson, even though Bessel himself did not make the first measurement.
1839, February : Henderson’s results published.
1848 : Discovery that α Centauri it is the closest of all the bright stars.
1870, 26th Sept : Assistant Government Astronomer H.C. Russell produces the first measurements from the 18.4cm. (7¼-inch) refractor. Position Angle 21.0°, Separation 9.8″. α Cen is measured by him thirty-six times, on one complete side of the orbital ellipse in the next twenty years, contributing significantly to the precision of the orbit we see today.
1874, 13th June at 6.00pm: ‘First-Light’ for the 29cm (11½-inch) refractor at Sydney Observatory. Russell measures PA as 30° 02′ The average separation found to be 7.71″. Seeing for the night described as excellent. Comment on the difference between the two refractors : “The small star looks a darker yellow than the larger one.” (Figure 7-1.)
1874-1894 : Henry Chamberlain Russell makes further observations from Sydney Observatory. Information of the binary nature was published in the Sydney Morning Herald in 1887.
Drawing by H.C. Russell of the Motion Alpha Centauri
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1891 : Final agreement is reached on the true attachment and period of the system.
1904 : Thomas Wright measures the radial velocity of the system using a spectrograph. α Cen A has the measured velocity of -19.1 km.s.-1, with the α Cen B measuring -24.47 km.s.-1. The mean velocity of the system is calculated as −21.7 km.s.-1 (towards us).
1915 : R.T.A. Innes discovers Proxima Centauri during his proper motion surveys from South Africa by blinking microscopy. It proves to be the closest star because of its position in the current orbit with the A+B system. Proxima is thought to be associated with A+B, even though it is 2.2° south-east. In the future, proper motions will slow down because of the true connection with A+B.
1922 : E.J. Hertzsprung publishes in his paper “List of Stars Nearer than 5 Parsecs” gives a first comparison list of the nearby stars to the sun, and states the parallaxes for all three stars of the system as 0.759 arcsec or 1.31 parsecs (4.30 light-years.) Proxima“s distance is soon shown to be slightly closer, instead making the nearest star 4.2 light-years. (It remained unknown if Proxima was positively associated with the principal A+B stars.)
1926 : Roberts, See, Doberek and Lahse calculate the first accurate orbit for the system.
1930 : System is found to be approaching the Sun by the observer Schlesinger at a mean value of −22.2 km.s.-1, being some 0.5 km.s.-1 lower than most current accepted values.
1933 : Distance of 4.2 light-years is universally adopted.
1948 : Distance of 4.3 light-years is universally adopted.
1955 : Closest approach in the apparent orbit by the separation of 1.61″.
1955, August : Closest approach in the true orbit (periastron) at 11.9 A.U.
1963 : My first observation through a small telescope.
1967 : Thackeray determines the radial velocity of Proxima is −15.7±3.3 km.s.-1.
1971 : First observation with my own telescope.
1978 : Kamper and Wesselink calculate that the total mass of all three stars is 2.13M⊙ (Solar Masses). They also find the distance of Proxima to be 1.295 parsecs (4.22 ly.), and the AB system as 1.333 parsecs (4.35 ly.) but 4.3 light years remains the adopted distance.
1978 : Flannery and Ayres determine age of the system, based on the luminosities and masses, as slightly older than the Sun at 6 billion years.
1980, May : Maximum apparent system separation is 22.6″.
1981, January : The ‘A’ star is found to be slightly variable, at around 0.65 magnitudes over the period of about twenty minutes.
1986: Van Altena at Yale University calculates the system’a age as 5.5±0.2 billion years.
1993 : Matthews and Gilmore questions the association of Proxima Centauri to the AB system. Velocity measured by Thackeray for Proxima seems too high for physical connection. They conclude Proxima is most likely a star passing close to the AB system. Later, using the ESO’s Coravel program in this same year, the results based on probability made again by Matthews and Gilmore reverse this decision, concluding likely association.
1994, January : Time of apastron in the true orbit begins to close.
1997, August : Hipparcos parallax data is finally released. Adopted distance is now 1.3478±0.0026pc. or 4.3955±0.0082 ly. from the most accurate parallax known to date of 0.74212″±0.00140 arcsec. This distance is universally adopted, but in reality, does decreases measurably from year to year until the system reaches closest approach to the Sun.
1999, May : Begins more notable differences in the telescope.
2000 : Position angle starts changing rapidly until around 2025. Apparent visual magnitude is -0.29v.
2002 : A paper published in Astronomy and Astrophysics of another set of orbital elements with higher precision. This was made by a collaboration whose author’s name is listed as the Belgian observer D. Pourbaix. This is abbreviated in the US Naval Observatory (USNO) WDS Reference file as Pbx2000b. One of the main differences is the quality grade of the orbit, which is now downgraded to Grade 2.
2005-2012 : Position angle and separation continue to change with the orientation, which is now notable different. Using the orbital elements of Pbx 2002, the following position angles and separations are calculated as follows;
******************** YEAR PA. Sep. ******************** 2005 229.7 10.574 2006 231.8 9.814 2007 234.3 9.050 2008 237.3 8.287 2009 240.9 7.532 2010 245.2 6.659 2011 250.5 6.092 2012 257.3 4.870 2013 265.7 4.870 2014 276.1 4.416 2015 288.4 4.125 ********************
2012, September : Position angle is exactly 270°
2012, 16th October : A discovery announcement was made for a new exoplanet component orbiting the secondary star. Now listed as α Cen Bb, the discovery was made using measurements of small radial velocity variations over three years, implying the minimum mass of 1.13±0.09 M⊙. Its short orbit period is 3.236 days. Although seemingly Earth-like, its orbit is merely 0.042 AU or six million kilometres from the star, placing it well inside the ideal habitable zone. Surface temperature estimates are about 1200°C. These results appear in the paper by Dumusque, X., et al., “An Earth mass planet orbiting Alpha Centauri B”, Nature, 491, 207 (2012)
2016, February : Separation closes to minimum of 4.01″ on western or following side. (PA=300.4°)
2020, July : Position angle is exactly 0° north.
2029, September : Secondary maximum separation reaches 10.44″. (PA = 19.8°)
2035, May : Periastron in the true orbit at 35 AU, being the first since 1955.
2037, August : Position angle is exactly 90° at 1.85″.
2037, November : Separation closes to 1.71″ eastern or preceding side. (PA is 112°) Changes in PA for five or six months reaches 5° degrees each month.
2038, May : Closest approach in apparent orbit at 2.58″.
2060, May : Maximum apparent separation again is 22.6″.
2073, November : True orbit again reaches apastron.
2998 A.D : The AB pair of α Centauri crosses the galactic plane at longitude ‘L’ 314.95°.
4000 AD : α Centauri and β Centauri points towards the true centre of the Cross.
6200 AD : α Centauri rapid proper motion produces a close approach or stellar conjunction with β Centauri. Minimum distance reaches 23′ or 1380″. Best stellar conjunction for 1st magnitude stars in the next 400,000 years.
10,000 AD: Barnard’s Star
makes its closest approach is 1.153 parsecs or 3.76 light years. This
is about 0.04 parsecs further than α
Centauri would be at this time, which shine now at +1.34 magnitude
— about the same brightness as present day Regulus / α Leonis.
Barnard’s star reaches its maximum
visual magnitude of 8.5, only one magnitude brighter than the current
9.5 magnitude. Currently this rapidly moving star is in Ophiuchus,
quite near 66 Oph (V2048 Oph). Sky Atlas 2000.0 has an insert
showing positions between 1900 and 2100 AD. By 10,000 AD,
Barnard’s star will be a far southern
object.
11,000 — 13,000 AD : True orbit closes until parallel to Earth’s orbital plane, where the orbit changes from direct motion to retrograde motion. At this time the system could acting like an eclipsing binary. Presently appears unlikely, as system period is too long and will likely miss.
17,400 AD : α Cen passes south of Gacrux (γ Crucis) by 34′. (1440″)
27,000 AD : α Cen lies at exactly 1 parsec away (3.26 light years) from the Sun.
29,240±1,370 AD : According to Robert Matthews
(1994) α Cen reaches its closest
approach to the Sun at merely 2.970±0.012 light years, when
the measured parallax will reach 1.098 mas. Apparent magnitude then
reaches −1.05±0.08, just greater than the current
brightness of Canopus.
Recent calculation by Jiménez-Torres et al. (2011) move the time
of closest approach back to 27,700±200 AD, when the mean
apparent velocity of 32.80±0.7 km.s-1 — some
10 km.s-1 faster than the current approaching mean radial
velocity of 22.7 km.s-1. This later paper suggest the
closest mean approach of the A+B system will be 0.975±0.02 pc.
or 3.18 light years, being very sightly further than Matthews (1994).
Jiménez-Torres et al. (2011) find that Proxima will be
fractionally closer at 0.95±0.01 pc or 3.10±0.03 light
years, when it will be travelling at the apparent velocity of
32.10±0.39 km.s-1
31,000 AD : System has moved 45° in the sky, approaching the border of the equatorial constellation of Hydra.
35,000 AD : Red dwarf star Ross 248 in the constellation of Andromeda (0.3°SE of Chi (χ) Andromedae) nearly becomes the closest star to the Sun at the distance of 3.023 light years or 0.927 parsecs, with the calculated error of +2,300 years, [Matthews; August, 1993]. Today (2005), Ross 248 has the higher radial velocity of -79.2±0.9km.s-1. By this date, velocity has increased by +3.8km.s.-1. Visual magnitude has changed from today’s +12.3 to +9.6 magnitude.
40 000 AD : Alpha Centauri becomes a northern hemisphere object. (Drats!)
41,000 AD : Star AC+79°3888 in the present constellation of Draco now (2004) some 3.4°N of λ Dra / Lambda Draconis then takes over from Ross 248 as the closest star at distances of about one parsec.
43,000 AD : AC+79°3888 reaches its nearest distance of 0.971 parsecs or 3.17 light years. Maximum magnitude for this red dwarf star reaches 7.2.
43,600 AD : α Centauri magnitude shines as −0.57, whose distance is 1.04pc. or 3.38 ly. This bright star now lies in the present day constellation of Hydra. Here, α Centauri makes a close approach to +1.98 magnitude Alphad / α Hydrae.
46,000 AD : Ross 248 becomes again further from the Sun than Proxima. However, Proxima in its long 100 000 year orbit becomes further than the A+B system.
50,000 AD : α Cen becomes again the closest star.
56,000 AD : α Cen again lies 4.4 light years away.
176,000 AD : α Cen reaches 3rd magnitude, whose distance is now 5.4pc. or 15.5 ly. This once prominent star has now lost much of its high proper motion observed today as it disappears towards the merge point. This is in the mid-northern part of the present constellation of Gemini.
264,000 AD : α Cen reaches 4th magnitude and whose distance is now 8.5pc. or 27.7 ly.
400,000 AD : α Cen shines as a 5th magnitude star, whose distance is 13.1pc. or 44 light years.
500,000 AD : Sirius is the same brightness as α Centauri is today. Vega is now the brightest star at −0.33 magnitude.
620,000 AD : α Cen reaches 6th magnitude to the naked-eye and whose distance is now 21.4pc. or 69.9 light-years.
c.690,000 AD : α Cen is now below naked-eye visibility for the first time in nearly 1.2 million years. This fainter system will prove as a telescopic resolution test. Proxima being exceeding difficult to spot with even the largest of telescopes, but who knows what technology with be available then! So then, the long reign of the so-called Imperial Star finally ends for us night-time observers of planet Earth orbiting around our home star named Sol.
c.2,000,000 AD : 2 million A.D.! : Perturbations by the close approach of the α Cen system, so long ago, possibly causes comets from the Oort Cloud to ‘rain’ down towards the Sun. According to the calculations of Bailey and Stagg (1990) and by Matthews (1993), over the period of twenty thousand years, when a maximum of two hundred thousand comets may possibly cross size of the Earth’s orbit, and equal to an unbelievable ten naked-eye naked-eye comets per year. For the Earth’s population, fear from a planetary collision would probably be realistic, though for the comet hunters — this would likely be pure heaven! Although they might end up being “snowed under”!
Note 1: Gravitational effects on the planets would not be adverse to their current orbits, as these effects are thousands of times too small.
Note 2: Distances are quoted from calculations made by Jahreiss & Morrison (1993) using the Gliese Catalogue. This catalogue is based on the closest stars to the Sun so far found by trigonometric parallaxes.
In finding and calculating some of the information in the history above, Robert Matthews’ “The Close Approach of Stars to the Solar Neighbourhood” by (QJRAS, 35, 2, pg.1-9 (1994)) has proved invaluable in calculating the changing positions and brightness of α Cen. This short and informative paper discusses the approach of other stars to the Solar System in the next 100,000 years, and also provides the formulae to do so. Some values quoted in this text have been updated to include information from the Hipparcos satellite data.
Data on the measurements featuring in Figures 2 & 3 on α Centauri’s orbit (published with Part 1 in the July issue) were kindly obtained from the late Dr. Geoff Douglass of the U.S. Naval Observatory.
Approximate apparent separation between any two stars in space is obtained from the parallax and the angle between them. This is easily calculated by:
Where:
TS1= True Separation expressed in parsecs or light years.
s = Separation in arc seconds.
D = Distance expressed in parsecs or light years.
Or, if distance is required in either kilometres or Astronomical Units then:
Where;
p = parallax in arc seconds.
To calculate the estimated period in solar years, which will be fairly inaccurate, apply Kepler’s Second Law using distances in astronomical units:
Southern Astronomical Delights © (2010)