View source for Barnard's Star

{{Starbox begin
| name = Barnard's Star
}}
{{Starbox image
| image = [[Image:Barnardstar2006.jpg|250px]]
| caption = The location of Barnard's Star
}}
{{Starbox observe
| epoch = [[J2000.0]]
| constell = [[Ophiuchus]]
| ra = {{RA|17|57|48.5}}<ref name="simbad">{{cite web | title=SIMBAD Query Result: V* V2500 Oph -- Variable of BY Dra type | publisher=Centre de Données astronomiques de Strasbourg | work=SIMBAD    | url=http://simbad3.u-strasbg.fr/sim-id.pl?protocol=html&Ident=BD%2B043561a | accessdate=October 16, 2007}}</ref>
| dec = {{DEC|+04|41|36}}<ref name="simbad" />
| appmag_v = 9.54<ref name="simbad" />
}}
{{Starbox character
| class = M4Ve<ref name="simbad" />
| appmag_1_passband = B
| appmag_1 = ~11.28<ref name="simbad" />
| appmag_2_passband = V
| appmag_2 = ~9.54<ref name="simbad" />
| appmag_3_passband = R
| appmag_3 = ~8.7<ref name="simbad" />
| appmag_4_passband = I
| appmag_4 = ~7.9<ref name="simbad" />
| appmag_5_passband = J
| appmag_5 = ~5.24<ref name="simbad" />
| appmag_6_passband = H
| appmag_6 = ~4.83<ref name="simbad" />
| appmag_7_passband = K
| appmag_7 = ~4.52<ref name="simbad" />
| r-i = <!--R-I color-->
| v-r = <!--V-R color-->
| b-v = 1.74<ref name="ARICNS">{{cite web |title=ARICNS 4C01453 |publisher=Astronomisches Rechen-Institut Heidelberg | date=March 4, 1998 | work=ARI Database for Nearby Stars |url=http://www.ari.uni-heidelberg.de/datenbanken/aricns/cnspages/4c01453.htm |accessdate=October 17, 2007}}</ref>
| u-b = 1.28<ref name="ARICNS"/>
| variable = [[BY Draconis variable|BY Draconis]]
}}
{{Starbox astrometry
| radial_v = -106.8<ref name="simbad" />
| prop_mo_ra = -798.71<ref name="simbad" />
| prop_mo_dec = 10337.77<ref name="simbad" />
| parallax = 545.4
| p_error = 0.3
| parallax_footnote = <ref>This parallax measurement and the subsequent distance calculation are taken from Benedict ''et al.'' (1999). SIMBAD suggests a parallax of 549.3 [[mas]] and thus a slightly lesser distance from Sol of 5.94 [[ly]].</ref>
| dist_ly = 
| dist_pc = 
| absmag_v = 13.22<ref name="ARICNS"/>
}}
{{Starbox detail
| source = <!--[source url]-->
| mass = 0.15-0.17<ref name="Dawson" />
| radius = 0.15<ref name="Ochsenbein" />-0.20<ref name="Dawson" />
| gravity = <!--Surface gravity (given as the base 10 logarithm expressed in cgs units)-->
| luminosity_visual = 0.0004<ref name="Dawson" />
| luminosity_bolometric = 0.0035<ref name="Dawson" />
| temperature = 3,134 ± 102<ref name="Dawson" />
| metal = 10-32% [[Sun]]<ref name="Gizis">{{cite journal | author = Gizis, John E. | year = 1997| month=February| title = M-Subdwarfs: Spectroscopic Classification and the Metallicity Scale | journal = The Astronomical Journal | url = {{Adsabs|1997AJ....113..806G}} | volume = 113 | issue = 2 | page = 820 | accessdate = August 24, 2006 | doi=10.1086/118302}}</ref>
| rotation = 130.4 [[day|d]]<ref name="Benedict1998" />
| age = ~1.0 × 10<sup>10</sup><ref name="Riedel2005" />
}}
{{Starbox catalog
| names = "Barnard's Runaway Star", [[Bonner Durchmusterung|BD]]+04°3561a, [[General Catalogue of Trigonometric Parallaxes|GCTP]]&nbsp;4098.00, [[Henry Lee Giclas|Gl]]&nbsp;140-024, [[Gliese-Jahreiss catalogue|Gliese]]&nbsp;699, [[Hipparcos Catalogue|HIP]]&nbsp;87937, [[Luyten Five-Tenths catalogue|LFT]]&nbsp;1385, [[Luyten Half-Second catalogue|LHS]]&nbsp;57, [[Luyten Two-Tenths catalogue|LTT]]&nbsp;15309, Munich&nbsp;15040, [[List of nearest stars|Proxima Ophiuchi]], [[Variable star designation|V2500 Ophiuchi]], ''[[Latin language|Velox Barnardi]]'', [[Alexander N. Vyssotsky|Vyssotsky]]&nbsp;799
}}
{{Starbox reference
| Simbad = BD%2B043561a
| ARICNS = 01453
}}
{{Starbox end}}

'''Barnard's Star''' ({{pron-en|ˈbɑrnərd}}), also known occasionally as '''Barnard's "Runaway" Star''',<ref>The name was attested just a year after its discovery: {{cite journal
 | doi=10.1038/099293a0 | year=1917 | month=June
 | title=Parallax of Barnard's "Runaway" Star
 | journal=[[Nature (magazine)|Nature]] | volume=99
 |pages=293–293 }}</ref> is a very low-mass [[red dwarf]] [[star]] approximately 6 [[light-year]]s away from Earth in the [[constellation]] of [[Ophiuchus]] (the Snake-holder). In 1916, American [[astronomer]] [[Edward Emerson Barnard|E. E. Barnard]] measured its [[proper motion]] as 10.3 [[Minute of arc|arcsecond]]s per year, which remains the largest known proper motion of any star relative to the [[Sun]].<ref name="EEB">{{cite journal
 | first=E. E. | last=Barnard
 | authorlink=Edward Emerson Barnard | year=1916
 | title=A small star with large proper motion
 | journal=Astronomical Journal | volume=29 | issue=695
 | page=181 | url={{adsabs|1916AJ.....29..181B}}
 | accessdate=2006-08-10 | doi = 10.1086/104156 }}</ref> At a distance of about 1.8 [[parsecs]], or just under six [[light-years]], Barnard's Star is the nearest known star in Ophiuchus, the second-closest known [[star system]] to the [[Sun]], and the [[List of nearest stars|fourth-closest]] known individual star to the Sun, after the three components of the [[Alpha Centauri]] system.  Despite its proximity, Barnard's Star at a dim [[apparent magnitude|magnitude]] 9 is not visible with the unaided eye. It is however much brighter in the [[infrared]] [[spectrum]].

Barnard's Star has been the subject of much study and has probably received more attention from astronomers than any other [[M dwarf]] star due to its proximity and favourable location for observation near the [[celestial equator]].<ref name="Dawson">{{cite journal
 | author=Dawson, P. C.; De Robertis, M. M. | year=2004
 | title=Barnard's Star and the M Dwarf Temperature Scale
 | journal=Astronomical Journal | volume=127 | issue=5
 | page=2909 | doi= 10.1086/383289 | url={{adsabs|2004AJ....127.2909D}} | accessdate=2006-08-16
}}</ref> Research has focused on stellar characteristics, [[astrometry]], and refining the limits of possible [[extrasolar planet]]s. Although it is an ancient star, observations suggest that Barnard's Star still experiences [[flare star|flare]] events.

The star has also been the subject of some controversy. For a decade, from the early 1960s, [[Peter van de Kamp]]'s erroneous claim of a gas giant [[planet]] (or planets) in orbit around Barnard's Star was accepted by other astronomers; while the presence of small terrestrial planets remains a possibility, the existence of massive planets has been largely discounted, and Van de Kamp's specific claims overturned. The star is notable as the target for [[Project Daedalus]], a study on the possibility of rapid, unmanned [[Interstellar travel|travel to nearby star systems]].

== Overview ==
Barnard's Star is a red dwarf of the dim M4 [[Stellar classification|spectral type]] and is too faint to see without a [[telescope]]. Its [[apparent magnitude]] is 9.57. This compares to −1.5 for [[Sirius]] (the brightest star in the night sky) and 6 for the faintest visible objects (the scale is [[logarithmic scale|logarithmic]], and so magnitude 9.57 is only about 1/27th of the brightness of the faintest star that can be seen by unaided human eyes under good viewing conditions).

At 7 to 12 billion years of age, Barnard's Star is considerably older than the Sun and may be among the oldest stars in the [[universe]];<ref name="Riedel2005">{{cite web
 | first=A. R. | last=Riedel | coauthors= Guinan, E. F.; DeWarf, L. E.; Engle, S. G.; McCook, G. P.
 | url={{adsabs|2005AAS...206.0904R}}
 | title=Barnard's Star as a Proxy for Old Disk dM Stars: Magnetic Activity, Light Variations, XUV Irradiances, and Planetary Habitable Zones | year=2005 | month=May
 | journal=Bulletin of the American Astronomical Society
 | volume=37 |page=442 | accessdate=2006-09-07 }}</ref> it has lost a great deal of rotational energy, and periodic changes in its light indicate it rotates just once every 130 days (compared to just over 25 days for the Sun).<ref name="Benedict1998" /> Given its age, Barnard's Star was long assumed to be quiescent in terms of stellar activity. However, in 1998 astronomers observed an intense [[stellar flare]], making it a surprising [[flare star]].<ref name=Flare>{{cite web
 | first=Ken | last=Croswell | year=2005 | month=November
 | url=http://www.astronomy.com/asy/default.aspx?c=a&id=3658
 | accessdate=2006-08-10 | title=A Flare for Barnard's Star
 | work=Astronomy Magazine | publisher=Kalmbach Publishing Co }}</ref> It has the [[variable star]] [[Variable star designation|designation]] V2500 Ophiuchi. In 2003 Barnard's Star provided the first detection of a change in the [[radial velocity]] of a star caused by its motion; further variability in its radial velocity was attributed to stellar activity.<ref name="Kurster" />

[[Image:Barnard2005.gif|thumb|200px|left|Barnard's Star, showing position every 5 years 1985–2005.]]
The proper motion of the body corresponds to a relative lateral speed ("sideways" relative to the Sun) of 90 [[kilometres per second]] (km/s). The 10.3 seconds of arc it travels annually amount to a quarter of a degree in a human lifetime, roughly half the angular diameter of the full Moon.<ref name="Kaler">{{cite web | first = James B. | last = Kaler | url = http://www.astro.uiuc.edu/~kaler/sow/barnard.html | title = Barnard's Star (V2500 Ophiuchi) | month = November | year = 2005 | work = Stars | publisher = James B. Kaler | accessdate = September 7, 2006}}</ref>

The radial velocity of Barnard's Star towards the Sun can be measured by its [[blue shift]]. Two measurements are given in [[Star catalogue|catalogue]]s: 106.8&nbsp;km/s  in [[SIMBAD]], and 110.8&nbsp;km/s in ARICNS and elsewhere. These measurements, combined with proper motion, suggest a true velocity relative to the Sun of 139.7 and 142.7&nbsp;km/s, respectively.<ref>''tv'' = (90² + 106.8²)<sup>½</sup> = 139.7, or ''tv'' = (90² + 110.8²)<sup>½</sup> = 142.7.  Stars with a large proper motion naturally have large true velocities relative to the Sun, but proper motion is also a function of proximity. While Barnard's Star has the largest proper motion, the largest known true velocity of another star in the [[Milky Way]] belongs to [[Wolf 424]] at 555 km/s.</ref> Barnard's Star will make its closest approach to the Sun around 11,700 AD, when it approaches to within some 3.8 light-years.<ref>{{cite journal | last=García-Sánchez | first=J. | coauthors=et al. | url={{adsabs|2001A%26A...379..634G}} | title=Stellar encounters with the solar system | journal=Astronomy & Astrophysics | volume=379 | page=642 | year=2001}}</ref> However, at that time it will not be the nearest star, as [[Proxima Centauri]] will have moved even closer to the Sun.<ref>{{cite journal | last=Matthews | first=R. A. J. | title=The Close Approach of Stars in the Solar Neighborhood | journal=Quarterly Journal of the Royal Astronomical Society | year=1994 | volume=35 | pages=1\u20139 | doi=10.1051/0004-6361:20011330 | bibcode=1994QJRAS..35....1M }}</ref> Barnard's Star will still be too dim to be seen with the naked eye at this time as its apparent magnitude will be about 8.5. After this it will steadily recede.

Barnard's Star is approximately 17% of a [[solar mass]] and has a radius 15–20% that of the [[Sun]];<ref name="Ochsenbein">{{cite journal |last=Ochsenbein |first=F.  |coauthors=Halbwachs, J. L. |year=1982 |month=March |title=A list of stars with large expected angular diameters |journal=Astronomy and Astrophysics Supplement Series |volume=47 |pages=523–531 |url={{adsabs|1982A%26AS...47..523O}} |accessdate= October 14, 2007}}</ref> in 2003 the radius was estimated as 0.20±0.008 [[solar radius|solar radii]], at the high end of the range typically provided, suggesting that previous estimates of the radius of Barnard's Star consistently underestimated the value<ref name="Dawson" />  Thus, although it is roughly 180 times the mass of Jupiter, its radius is only 1.5 to 2.0 times larger, reflecting the tendency of objects in the [[brown dwarf]] range to be about the same size.  Its [[effective temperature]] is 3,134(±102) [[kelvin|K]], and it has a visual luminosity just 4/10,000ths of solar luminosity, corresponding to a bolometric luminosity of 34.6/10,000ths.<ref name ="Dawson" />  It is so faint that if it were at the same distance from Earth as the Sun is, it would appear only 100 times brighter than a full moon.<ref name="SolStation">{{cite web | url = http://www.solstation.com/stars/barnards.htm | title = Barnard's Star | publisher = Sol Station|accessdate = August 10, 2006}}</ref>

In a broad survey of the [[metallicity]] of M dwarf stars, Barnard's Star's was placed between −0.5 and −1.0 on the metallicity scale, which is roughly 10 to 32% of the value for the Sun.<ref name="Gizis" />  Metallicity, the proportion of stellar mass made up of elements heavier than [[helium]], helps classify stars relative to the galactic population.  Barnard's Star seems to be typical of the old, red dwarf [[population II star]]s, yet these are also generally metal-poor [[halo star]]s.  While sub-solar, Barnard's Star's metallicity is higher than a halo star and is in keeping with the low end of the metal-rich [[disk star]] range; this, plus its high space motion, have led to the designation "Intermediate Population II star", between a halo and disk star.<ref name="Gizis" /><ref name="Kurster">{{cite journal | last=Kürster | first=M. | coauthors=et al. | year = 2003 | title = The low-level radial velocity variability in Barnard's Star | journal = Astronomy and Astrophysics | url = {{adsabs|2003A&A...403.1077K}} | doi = 10.1051/0004-6361:20030396 | volume = 403 | issue = 6 | page = 1077 | accessdate = August 16, 2006}}</ref>

== Claims of a planetary system ==

For a decade from 1963 onwards, a substantial number of astronomers accepted a claim by [[Peter van de Kamp]] that he had detected, by using [[Methods of detecting extrasolar planets#Astrometry|astrometry]], a perturbation in the [[proper motion]] of Barnard's Star consistent with its having one or more planets comparable in mass with [[Jupiter]].<ref name=Bell>{{cite web | first = George H. | last = Bell | url = http://www.public.asu.edu/~sciref/exoplnt.htm#section2 | month = April | year = 2001 | title = The Search for the Extrasolar Planets: A Brief History of the Search, the Findings and the Future Implications, Section 2 | publisher = Arizona State University | accessdate = August 10, 2006}} ''Full description of the Van de Kamp planet controversy.'' </ref> Van de Kamp had been observing the star from 1938, attempting, with colleagues at the [[Swarthmore College]] observatory, to find minuscule variations of 1 [[micrometre]] in its position on [[photographic plates]] consistent with [[orbital perturbation]]s (wobbles) in the star that would indicate a planetary companion; this involved as many as ten people averaging their results in looking at plates, to avoid systemic, individual errors.<ref name="Blunder">{{cite web | url = http://www.astrobio.net/news/article1635.html | title = The Barnard's Star Blunder | year = 2005 | month=July| work = Astrobiology Magazine | accessdate = August 9, 2006}}</ref> Van de Kamp's initial suggestion was a 1.6 Jupiter mass planet at 4.4 AU in a slightly eccentric orbit, and these measurements were apparently refined in a 1969 paper. Later that year he suggested two planets of 1.1 and 0.8 Jupiter masses.<ref>{{cite journal | author = Van de Kamp, Peter. | year = 1969 | title = Alternate dynamical analysis of Barnard's star | journal = Astronomical Journal | volume = 74 | issue = 8 | page = 757 | url = {{adsabs|1969AJ.....74..757V}} | accessdate = August 10, 2006 | doi = 10.1086/110852}}</ref>

[[Image:RedDwarfPlanet.jpg|thumb|right|An artist's conception of a planet in orbit around a red dwarf star.]]

Other astronomers subsequently repeated Van de Kamp's measurements, and two important papers in 1973 undermined the claim of a planet or planets. [[George Gatewood]] and [[Heinrich Eichhorn]], at a different observatory and using newer plate measuring techniques, failed to verify the planetary companion.<ref>{{cite journal | author = Gatewood, George, and Eichhorn, H. | year = 1973 | title = An unsuccessful search for a planetary companion of Barnard's star (BD +4 3561) | url={{adsabs|1973AJ.....78..769G}} | journal = Astronomical Journal | volume = 78 | issue = 10 | page = 769 | accessdate = August 9, 2006 | doi = 10.1086/111480}}</ref> Another paper published by [[John L. Hershey]] four months earlier, also using the Swarthmore observatory, found that changes in the astrometric field of various stars correlated to the timing of adjustments and modifications that had been carried out on the telescopic lens;<ref>{{cite journal | author = John L. Hershey | year = 1973 | title = Astrometric analysis of the field of AC +65 6955 from plates taken with the Sproul 24-inch refractor | journal = Astronomical Journal | volume = 78 | issue = 6 | page = 421 
| url=http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?1973AJ.....78..421H&amp;data_type=PDF_HIGH&amp;whole_paper=YES&amp;type=PRINTER&amp;filetype=.pdf
| doi = 10.1086/111436 |accessdate = August 9, 2006}}</ref> the planetary "discovery" was an artifact of maintenance and upgrade work.

Van de Kamp never acknowledged any error and published a further confirmation of two planets' existence as late as 1982<ref>{{cite journal | author = Van de Kamp, Peter. | year = 1982 | title = The planetary system of Barnard's star | journal = Vistas in Astronomy | volume = 26 | issue = 2 | page = 141 | url = {{adsabs|1982VA.....26..141V}} | doi = 10.1016/0083-6656(82)90004-6 | accessdate = August 10, 2006}}</ref> (he died in 1995). [[Wulff Heintz]], Van de Kamp's successor at Swarthmore and an expert on [[double stars]], questioned his findings and began publishing criticisms from 1976 onwards; the two are reported to have become estranged because of this.<ref name=Swathmore>{{cite web | first = Bill | last =Kent | url = http://www.swarthmore.edu/Admin/publications/bulletin/mar01/wobble.html | title = Barnard's Wobble | year = 2001 | work = Bulletin | publisher = Swarthmore College | accessdate = August 9, 2006}}</ref>

The controversy did heighten the profile of Barnard's Star. During the period that the planetary claim was accorded credibility, the star's fame among the [[science fiction]] community grew (see [[Stars_and_planetary_systems_in_fiction#Barnard.27s_Star|Barnard's Star in fiction]]),{{Fact|date=May 2009}} and it was adopted as a target for [[Project Daedalus]].{{Fact|date=May 2009}}

=== Refining planetary boundaries ===
While not completely ruling out the possibility of planets, null results for planetary companions continued throughout the 1980s and 90s, the latest based on [[interferometric]] work with the [[Hubble space telescope]] in 1999.<ref name = Hubble99>{{cite journal | author=Benedict ''et al.'' | year=1999 | month=August | title = Interferometric Astrometry of Proxima Centauri and Barnard's Star Using Hubble Space Telescope Fine Guidance Sensor 3: Detection Limits for sub-Stellar Companions 
| url=http://www.iop.org/EJ/article/1538-3881/118/2/1086/990089.text.html
| journal = The [[Astronomical Journal]] | volume=118 | issue=2 | pages=1086-1100 | doi=10.1086/300975}}</ref> By refining the values of a star's motion, the mass and orbital boundaries for possible planets are tightened: in this way astronomers are often able to describe what types of planets ''cannot'' orbit a star.

M dwarfs such as Barnard's Star are more easily studied than larger stars in this regard because their lower mass renders perturbations more obvious.<ref>{{cite journal | author =  Michael Endl, William D. Cochran, Robert G. Tull, and Phillip J. MacQueen. | year = 2003 | title = A Dedicated M Dwarf Planet Search Using the Hobby-Eberly Telescope | journal = The Astronomical Journal | url = http://www.journals.uchicago.edu/doi/full/10.1086/379137 | doi = 10.1086/379137 | volume = 126 | issue = 12 | page = 3099 | accessdate = August 18, 2006}}</ref> Gatewood was thus able to show in 1995 that planets of 10 Jupiter masses (the lower limit for [[brown dwarfs]]) were impossible around Barnard's Star,<ref name="Bell" /> in a paper which helped refine the negative certainty regarding planetary objects in general.<ref name="Gatewood95">{{cite journal|author=George D. Gatewood|title=A study of the astrometric motion of Barnard's star |journal= Journal Astrophysics and Space Science |volume= 223|issue = 1 |year= 1995|pages= 91–98| doi=10.1007/BF00989158|url=http://www.springerlink.com/content/q722p32q2h28kp50/}}</ref> In 1999, work with the Hubble Space Telescope further excluded planetary companions of 0.8 Jupiter mass with an orbital period of less than 1,000 days,<ref name="Hubble99" /> while Kurtzer determined in 2003 that within the [[habitable zone]] around Barnard's Star, planets are not possible with an "''M''&nbsp;sin&nbsp;''i''" value<ref>"''M''&nbsp;sin&nbsp;''i''" means the mass of the planet times the sine of the angle of inclination of its orbit, and hence provides the minimum mass for the planet.</ref> greater than 7.5 Earth masses or with a mass greater than 3.1 Neptune masses (much lower than van de Kamp's smallest suggested value).<ref name="Kurster" />

While this research has greatly restricted the possible properties of planets around Barnard's Star, it has not ruled them out completely; [[terrestrial planets]] would be difficult to detect. [[NASA]]'s [[Space Interferometry Mission]] and the [[ESA]]'s [[Darwin (ESA)|Darwin]], both scheduled to begin looking for extrasolar Earth-like planets around 2015, have chosen Barnard's Star as a search target.<ref name="SolStation" />

== Project Daedalus ==
{{main|Project Daedalus}}

Excepting the planet controversy, the best known study of Barnard's Star was part of [[Project Daedalus]]. Undertaken between 1973 and 1978, it suggested that rapid, unmanned travel to another star system is possible with existing or near-future technology.<ref name="Daedalus76">{{cite journal | author =  Bond, A., and Martin, A.R. | year = 1976 | title =  Project Daedalus&nbsp;— The mission profile | journal =  [[Journal of the British Interplanetary Society]] | url = http://md1.csa.com/partners/viewrecord.php?requester=gs&collection=TRD&recid=A7618970AH&q=project+daedalus&uid=788304424&setcookie=yes | volume = 29 | issue = 2 | page = 101 | accessdate = August 15, 2006}}</ref> Barnard's Star was chosen as a target, partly because it was believed to have planets.<ref name=DarlingDaedalus>{{cite web | first = David | last = Darling | url = http://www.daviddarling.info/encyclopedia/D/Daedalus.html | title = Daedalus, Project | month = July |year=2005 | work = The Encyclopedia of Astrobiology, Astronomy, and Spaceflight | accessdate = August 10, 2006}}</ref>

The theoretical model suggested that a nuclear pulse rocket employing [[nuclear fusion]] (specifically, electron bombardment of [[deuterium]] and [[helium-3]]) and accelerating for four years could achieve a velocity of 12% of the [[speed of light]]. The star could then be reached in 50 years, within a human lifetime.<ref name="DarlingDaedalus" /> Along with detailed investigation of the star and any companions, the [[interstellar medium]] would be examined and baseline astrometric readings performed.<ref name="Daedalus76" />

The initial Project Daedalus model sparked further theoretical research. In 1980, [[Robert Freitas]] suggested a more ambitious plan: a [[self-replicating spacecraft]] intended to search for and make contact with [[extraterrestrial life]].<ref name=Repro>{{cite journal | first=Robert A., Jr. | last=Freitas | title=A Self-Reproducing Interstellar Probe | journal=[[Journal of the British Interplanetary Society]] | volume=33 | month=July | year=1980 | pages=251–264 | url=http://www.rfreitas.com/Astro/ReproJBISJuly1980.htm | accessdate =October 1, 2008}}</ref> Built and launched in [[Jupiter|Jovian]] orbit, it would reach Barnard's Star in 47 years under parameters similar to those of the original Project Daedalus. Once at the star, it would begin automated self-replication, constructing a factory, initially to manufacture exploratory probes and eventually to create a copy of the original spacecraft after 1,000 years.<ref name="Repro" />

== 1998 flare ==

The observation of a [[stellar flare]] on Barnard's Star has added another element of interest to its study. Noted by William Cochran, University of Texas at Austin, based on changes in the [[spectral emissions]] on July 17, 1998 (during an unrelated search for planetary "wobbles"), it was four more years before the flare was fully analyzed. At that point Diane Paulson ''et al.'', now of [[Goddard Space Flight Center]], suggested that the flare's temperature was 8000 K, more than twice the normal temperature of the star, although simply analyzing the spectra cannot precisely determine the flare's total output.<ref name="Paulson">{{cite journal | first = Diane B. | last = Paulson | coauthors=et al. | year = 2006 | title = Optical Spectroscopy of a Flare on Barnard's Star | journal = Publications of the Astronomical Society of the Pacific | url = http://www.journals.uchicago.edu/doi/abs/10.1086/499497 | volume = 118 | issue = 1 | page = 227 | doi=10.1086/499497 | accessdate = August 21, 2006 | format = abstract}}</ref>  Given the essentially random nature of flares, she noted "the star would be fantastic for amateurs to observe".<ref name="Flare" />

[[Image:RedDwarfNASA-hue-shifted.jpg|right|thumb|Artist's conception. Barnard's Star is a [[red dwarf]], like most of its neighbours.]]

The flare was surprising because intense stellar activity is not expected around stars of such age. Flares are not completely understood, but are believed to be caused by strong [[magnetic fields]] which suppress [[plasma (physics)|plasma]] [[convection]] and lead to sudden outbursts: strong magnetic fields occur in rapidly rotating stars, while old stars tend to rotate slowly. An event of such magnitude around Barnard's Star is thus presumed to be a rarity.<ref name="Paulson" /> Research on the star's [[periodicity]], or changes in stellar activity over a given timescale, also suggest it ought to be quiescent; 1998 research showed weak evidence for periodic variation in Barnard's Star's brightness, noting only one possible starspot over 130 days.<ref name="Benedict1998">{{cite journal | last= Benedict | first=G. Fritz | coauthors=et al. | year = 1998 | title = Photometry of Proxima Centauri and Barnard's star using Hubble Space Telescope fine guidance senso 3 | journal = The Astronomical Journal | url = {{adsabs|1998AJ....116..429B}} | volume = 116 | issue = 1 | page = 429 | accessdate = August 18, 2006 | doi= 10.1086/300420}}</ref>

Stellar activity of this sort has created interest in using Barnard's Star as a proxy to understand similar stars. Photometric studies of its [[X-ray]] and [[UV]] emissions are hoped to shed light on the large population of old M dwarfs in the galaxy. Such research has [[astrobiology|astrobiological]] implications: given that the habitable zones of M dwarfs are close to the star, any planets would be strongly influenced by solar flares, winds, and plasma ejection events.<ref name="Riedel2005" />

== Neighborhood ==

Barnard's Star can be viewed directly overhead just north of the equator, at 4° N; theoretically viewable ± 90° from this point, it can thus be observed at most Earth latitudes, although [[Extinction (astronomy)|atmospheric extinction]] will reduce visibility when it is near the horizon in the extreme north and south.

The star shares much the same neighbourhood as the Sun. The neighbours of Barnard's Star are generally of red dwarf size, the smallest and most common star type. Its closest neighbour is currently the red dwarf [[Ross 154]], at 1.66 pc or 5.41 ly distance. The Sun and [[Alpha Centauri]] are, respectively, the next closest systems.<ref name=SolStation/> From Barnard's Star, the Sun would appear on the diametrically opposite side of the sky at coordinates RA={{RA|5|57|48.5}}, Dec={{DEC|−04|41|36}}, in the eastern part of the constellation [[Monoceros]]. The absolute magnitude of the Sun is 4.83 and at a distance of 1.834 parsecs, it would be an impressively bright first-magnitude star, like [[Pollux (star)|Pollux]] to us.<ref>The Sun's apparent magnitude from Barnard's Star: <math>\begin{smallmatrix} m = 4.83 + 5\cdot((\log_{10} 1.834) - 1) = 1.15 \end{smallmatrix}</math>.</ref>

== See also ==
{{commonscat}}
* [[List of nearest stars]]
* [[List of stars named after people]]
* [[Stars and planetary systems in fiction#Barnard's Star|Barnard's star in fiction]]

== Notes and references ==
{{reflist|2}}
== External links ==

* {{cite web |url=http://www.solstation.com/stars/barnards.htm |title=Barnard's Star|work=SolStation}}
*{{cite web | first = David | last = Darling | url = http://www.daviddarling.info/encyclopedia/B/BarnardsStar.html | title = Barnard's Star | work = The Encyclopedia of Astrobiology, Astronomy, and Spaceflight}}
*{{cite web | last = Schmidling | first = Jack | url = http://schmidling.com/barnard.htm | title = Barnard's Star | work = Jack Schmidling Productions, Inc}} Amateur work showing Barnard's Star movement over time.

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[[Category:Discoveries by E. E. Barnard]]
[[Category:HIP objects|087937]]
[[Category:Ophiuchus constellation]]
[[Category:M-type main sequence stars]]
[[Category:Stars with proper names]]

[[ca:Estel de Barnard]]
[[cs:Barnardova šipka]]
[[de:Barnards Pfeilstern]]
[[es:Estrella de Barnard]]
[[fa:ستاره بارنارد]]
[[fr:Étoile de Barnard]]
[[ga:Réalta Barnard]]
[[ko:바너드 별]]
[[it:Stella di Barnard]]
[[he:כוכב ברנרד]]
[[ka:ბარნარდის ვარსკვლავი]]
[[lv:Bārnarda zvaigzne]]
[[lb:Feilstär vum Barnard]]
[[lt:Barnardo žvaigždė]]
[[hu:Barnard-csillag]]
[[nl:Ster van Barnard]]
[[ja:バーナード星]]
[[no:Barnards stjerne]]
[[nov:Stele de Barnard]]
[[pl:Gwiazda Barnarda]]
[[pt:Estrela de Barnard]]
[[ru:Звезда Барнарда]]
[[sk:Barnardova hviezda]]
[[sl:Barnardova zvezda]]
[[fi:Barnardin tähti]]
[[sv:Barnards stjärna]]
[[uk:Зоря Барнарда]]
[[zh:巴納德星]]