Editing Pleiades (section)

== Distance ==
{{Location mark
|type=thumb|caption=Location of Pleiades (circled) in the [[night sky]]
|image=Taurus constellation map.svg|alt=|float=left|width=260
|label=|position=left
|mark=Red circle.svg|mark_width=20|mark_link=λ Tau
|x=810|y=320
}}
The distance to the Pleiades can be used as a key first step to calibrate the [[cosmic distance ladder]]. As the cluster is relatively close to the Earth, the distance should be relatively easy to measure and has been estimated by many methods. Accurate knowledge of the distance allows astronomers to plot a [[Hertzsprung–Russell diagram]] for the cluster, which, when compared with those plotted for clusters whose distance is not known, allows their distances to be estimated. Other methods may then extend the distance scale from open clusters to galaxies and clusters of galaxies, and a cosmic distance ladder may be constructed. Ultimately astronomers' understanding of the age and future evolution of the universe is influenced by their knowledge of the distance to the Pleiades. Yet some authors argue that the controversy over the distance to the Pleiades discussed below is a [[red herring]], since the cosmic distance ladder can (presently) rely on a suite of other nearby clusters where consensus exists regarding the distances as established by the ''[[Hipparcos]]'' satellite and independent means (e.g., the [[Hyades (star cluster)|Hyades]], the [[Coma Star Cluster|Coma Berenices cluster]], etc.).<ref name=majaess11>{{Cite journal|arxiv=1102.1705|last1= Majaess|first1= Daniel J.|title= Deep Infrared ZAMS Fits to Benchmark Open Clusters Hosting delta Scuti Stars|journal= Journal of the American Association of Variable Star Observers (Jaavso)|volume= 39|issue= 2|pages= 219|last2=  Turner|first2= David G.|last3=  Lane|first3= David J.|last4= Krajci|first4= Tom|date= 2011|bibcode= 2011JAVSO..39..219M}}</ref>

[[File:Astro 4D m45 cr anim.gif|upright|thumb|Animation of proper motion in 400,000 years—[[Autostereogram#3D perception|cross-eyed viewing]] [[File:Stereogram guide cross-eyed.svg|10px]] (click for viewing guide)]]

Measurements of the distance have elicited much controversy. Results prior to the launch of the ''Hipparcos'' satellite generally found that the Pleiades were approximately 135 [[parsec]]s (pc) away from Earth. Data from ''Hipparcos'' yielded a surprising result, namely a distance of only 118 pc, by measuring the [[parallax]] of stars in the cluster—a technique that should yield the most direct and accurate results. Later work consistently argued that the ''Hipparcos'' distance measurement for the Pleiades was erroneous:<ref name=majaess11/><ref name="Percival">{{cite journal
 |author=Percival, S. M.
 |author2=Salaris, M.
 |author3=Groenewegen, M. A. T.
 |date=2005
 |title=The distance to the Pleiades. Main sequence fitting in the near infrared
 |journal=[[Astronomy and Astrophysics]]
 |volume=429 |pages=887–894
 |bibcode=2005A&A...429..887P
|doi=10.1051/0004-6361:20041694
|arxiv = astro-ph/0409362
 |issue=3 |s2cid=14842664
 }}</ref><ref name="Zwahlen">
{{cite journal
 |display-authors=4
 |author=Zwahlen, N.
 |author2=North, P.
 |author3=Debernardi, Y.
 |author4=Eyer, L.
 |author5=Galland, F.
 |author6=Groenewegen, M. A. T.
 |author7=Hummel, C. A.
 |date=2004
 |title=A purely geometric distance to the binary star Atlas, a member of the Pleiades
 |journal=[[Astronomy and Astrophysics Letters]]
 |volume=425 |pages=L45
 |bibcode=2004A&A...425L..45Z
 |doi=10.1051/0004-6361:200400062
|arxiv = astro-ph/0408430
 |issue=3 |s2cid=37047575
 }}</ref><ref name=soderblom05>
{{cite journal
 |display-authors=4
 |author=Soderblom D. R.
 |author2=Nelan E.
 |author3=Benedict G. F.
 |author4=McArthur B.
 |author5=Ramirez I.
 |author6=Spiesman W.
 |author7=Jones B. F.
 |date=2005
 |title=Confirmation of Errors in Hipparcos Parallaxes from Hubble Space Telescope Fine Guidance Sensor Astrometry of the Pleiades
 |journal=[[Astronomical Journal]]
 |volume=129 |pages=1616–1624
 |bibcode=2005AJ....129.1616S
 |doi=10.1086/427860
|arxiv = astro-ph/0412093
 |issue=3 |s2cid=15354711
 }}</ref><ref>
{{cite journal
 |author=Turner, D. G.
 |date=1979
 |title=A reddening-free main sequence for the Pleiades cluster
 |journal=[[Publications of the Astronomical Society of the Pacific]]
 |volume=91 |pages=642–647
 |bibcode=1979PASP...91..642T
 |doi=10.1086/130556
|doi-access=free
 }}</ref><ref name=pan04>
{{cite journal
 |author=Pan, X.
 |date=2004
 |title=A distance of 133-137 parsecs to the Pleiades star cluster
 |journal=[[Nature (journal)|Nature]]
 |volume=427 |issue=6972
 |pages=326–328
 |bibcode=2004Natur.427..326P
 |doi=10.1038/nature02296
 |pmid=14737161
|s2cid=4383850
 }}</ref> In particular, distances derived to the cluster via the [[Hubble Space Telescope]] and infrared [[Hertzsprung–Russell diagram|color–magnitude diagram]] fitting (so-called "[[spectroscopic parallax]]") favor a distance between 135 and 140 pc;<ref name=majaess11/><ref name=soderblom05/> a dynamical distance from [[Interferometry|optical interferometric]] observations of the inner pair of stars within [[Atlas (star)|Atlas]] (a bright triple star in the Pleiades) favors a distance of 133 to 137 pc.<ref name=pan04/> However, the author of the 2007–2009 catalog of revised ''Hipparcos'' parallaxes reasserted that the distance to the Pleiades is ~120 pc and challenged the dissenting evidence.<ref name=vanleeuwen09>{{Cite journal|bibcode=2009A&A...497..209V |title=Parallaxes and proper motions for 20 open clusters as based on the new Hipparcos catalogue |journal=[[Astronomy and Astrophysics]] |volume=497 |issue=1 |pages=209–242 |last1=Van Leeuwen |first1=F. |date=2009 |doi=10.1051/0004-6361/200811382 |arxiv = 0902.1039 |s2cid=16420237 }}</ref> In 2012, Francis and Anderson<ref>
{{cite journal
 |author=Francis C.
 |author2=Anderson E.
 |date=2012
 |title=XHIP II: clusters and associations
 |journal=[[Astronomy Letters]]
 |arxiv = 1203.4945 |bibcode = 2012AstL...38..681F
 |volume=1203
 |issue=11
 |pages=4945
 |doi=10.1134/S1063773712110023|s2cid=119285733
 }}</ref> proposed that a systematic effect on ''Hipparcos'' parallax errors for stars in clusters would bias calculation using the [[Weighted arithmetic mean|weighted mean]]; they gave a ''Hipparcos'' parallax distance of 126 pc and [[Photometry (astronomy)|photometric]] distance of 132 pc based on stars in the [[AB Doradus moving group|AB Doradus]], [[Tucana-Horologium association|Tucana-Horologium]] and [[Beta Pictoris moving group|Beta Pictoris]] moving groups, which are all similar in age and composition to the Pleiades. Those authors note that the difference between these results may be attributed to random error.
More recent results using [[very-long-baseline interferometry]] (VLBI) (August 2014), and preliminary solutions using [[Gaia (spacecraft)|Gaia]] Data Release 1 (September 2016) and Gaia Data Release 2 (August 2018), determine distances of 136.2 ± 1.2 pc,<ref name=vlbi14>
{{Cite journal
 |display-authors= 4
 |first1= Carl |last1= Melis
 |first2= Mark J. |last2= Reid
 |first3= Amy J. |last3= Mioduszewski
 |first4= John R. |last4= Stauffer
 |first5= Geoffrey |last5= Bower
 |date= 29 August 2014
 |title= A VLBI resolution of the Pleiades distance controversy
 |journal= Science
 |volume= 345 |issue= 6200 |pages= 1029–1032
 |doi= 10.1126/science.1256101
 |pmid= 25170147 |arxiv = 1408.6544 |bibcode = 2014Sci...345.1029M |s2cid= 34750246 }} See also commentary by
{{Citation
 |first1= Léo |last1= Girardi
 |date= 29 August 2014
 |title= One good cosmic measure
 |journal= Science
 |volume= 345 |issue= 6200 |pages= 1001–1002
 |doi= 10.1126/science.1258425
 |pmid= 25170136
 |bibcode = 2014Sci...345.1001G |s2cid= 5359091
 }}
</ref> 134 ± 6 pc<ref name=abrown>{{Citation
 | author = Anthony G. A. Brown
 | author2 = GAIA Collaboration
 | date = 2016
 | title = Gaia Data Release 1. Summary of the astrometric, photometric, and survey properties
 | type = forthcoming article
 | journal = Astronomy and Astrophysics
 | doi = 10.1051/0004-6361/201629512
 | url = http://www.aanda.org/articles/aa/pdf/forth/aa29512-16.pdf
 | access-date = 14 September 2016
 | bibcode=2016A&A...595A...2G
 | volume=595
 | page=A2
 | arxiv = 1609.04172
 | s2cid = 1828208
 }}</ref> and 136.2 ± 5.0 pc,<ref name="Abramson2018">{{cite journal |last1=Abramson |first1=Guillermo |title=The Distance to the Pleiades According to Gaia DR2 |journal=Research Notes of the AAS |date=20 August 2018 |volume=2 |issue=3 |pages=150 |doi=10.3847/2515-5172/aada8b|bibcode=2018RNAAS...2..150A |doi-access=free |hdl=11336/94435 |hdl-access=free }}</ref> respectively. The Gaia Data Release&nbsp;1 team were cautious about their result, and the VLBI authors assert "that the ''Hipparcos''-measured distance to the Pleiades cluster is in error".

The most recent distance estimate of the distance to the Pleiades based on the [[Gaia Data Release 3]] is {{val|135.74|0.10|u=pc}}.<ref name="Alfonso2023">{{cite journal |last1=Alfonso |first1=Jeison |last2=García-Varela |first2=Alejandro |title=A Gaia astrometric view of the open clusters Pleiades, Praesepe, and Blanco 1 |journal=Astronomy & Astrophysics |date=September 2023 |volume=677 |pages=A163 |doi=10.1051/0004-6361/202346569|arxiv=2304.00164 |bibcode=2023A&A...677A.163A }}</ref>

{| class="wikitable plainrowheaders" style="margin-right: 0; margin-left: 1em; text-align: center;"
|+ Selected distance estimates to the Pleiades
! scope="col" | Year
! scope="col" | Distance ([[parsec|pc]])
! scope="col" | Notes
|-
! scope="row" | 1999
| 125
| ''[[Hipparcos]]''<ref name=hipparcos1999>{{cite journal|bibcode=1999A&A...341L..71V|title=HIPPARCOS distance calibrations for 9 open clusters|journal=Astronomy and Astrophysics|volume=341|pages=L71|last1=Van Leeuwen|first1=Floor|year=1999}}</ref>
|-
! scope="row" | 2004
| 134.6 ± 3.1
| Hubble [[Fine Guidance Sensor (HST)|Fine Guidance Sensor]]<ref name="soderblom05" />
|-
! scope="row" | 2009
| 120.2 ± 1.9
| Revised ''Hipparcos''<ref name=vanleeuwen09/>
|-
! scope="row" | 2014
| 136.2 ± 1.2
| [[Very-long-baseline interferometry]]<ref name=vlbi14/>
|-
! scope="row" | 2016
| 134 ± 6
| [[Gaia Data Release 1]]<ref name=abrown/>
|-
! scope="row" | 2018
| 136.2 ± 5.0
| [[Gaia Data Release 2]]<ref name=Abramson2018/>
|-
! scope="row" | 2023
| {{val|135.74|0.10|u=pc}}
| [[Gaia Data Release 3]]<ref name="Alfonso2023"/>
|-
|}