Editing Star (section)

===Kinematics===
{{Main|Stellar kinematics}}
[[File:Pleiades large.jpg|thumb|The [[Pleiades]], an [[open cluster]] of stars in the [[constellation]] of [[Taurus (constellation)|Taurus]]. These stars share a common motion through space.<ref>{{cite journal
 | last=Loktin | first=A. V.
 | title=Kinematics of stars in the Pleiades open cluster
 | journal=Astronomy Reports | volume=50 | issue=9
 | pages=714–721 |date=September 2006
 | doi=10.1134/S1063772906090058 | bibcode=2006ARep...50..714L| s2cid=121701212
 }}</ref>]]

The motion of a star relative to the Sun can provide useful information about the origin and age of a star, as well as the structure and evolution of the surrounding galaxy.<ref>{{cite book
 | title=The Origin of the Galaxy and Local Group
 | series=Saas-Fee Advanced Course 37 Swiss Society for Astrophysics and Astronomy
 | first1=Joss | last1=Bland-Hawthorn | first2=Kenneth | last2=Freeman | first3=Francesca | last3=Matteucci
 | date=2014 | page=114 | isbn=978-3642417207
 | publisher=Springer Berlin Heidelberg
 | editor-first=Ben | editor-last=Moore
 | chapter=Appendix B: Stellar Data: Sources and Techniques
 | chapter-url=https://books.google.com/books?id=pTTABAAAQBAJ&pg=PA114 }}</ref> The components of motion of a star consist of the [[radial velocity]] toward or away from the Sun, and the traverse angular movement, which is called its proper motion.<ref>{{cite book
 | title=Observational Astronomy
 | first1=D. Scott | last1=Birney | first2=Guillermo | last2=Gonzalez | first3=David | last3=Oesper
 | date=2006 | pages=72–79 | isbn=978-1316139400
 | publisher=Cambridge University Press
 | url=https://books.google.com/books?id=vrA-BAAAQBAJ&pg=PA73 }}</ref>

Radial velocity is measured by the [[doppler shift]] of the star's spectral lines and is given in units of km/[[second|s]]. The proper motion of a star, its parallax, is determined by precise astrometric measurements in units of milli-[[arc second]]s (mas) per year. With knowledge of the star's parallax and its distance, the proper motion velocity can be calculated. Together with the radial velocity, the total velocity can be calculated. Stars with high rates of proper motion are likely to be relatively close to the Sun, making them good candidates for parallax measurements.<ref>{{cite web
 | date=1999-09-10 | url=http://www.rssd.esa.int/index.php?project=HIPPARCOS
 | title=Hipparcos: High Proper Motion Stars
 | publisher=ESA | access-date=2006-10-10}}</ref>

When both rates of movement are known, the [[space velocity (astronomy)|space velocity]] of the star relative to the Sun or the galaxy can be computed. Among nearby stars, it has been found that younger population I stars have generally lower velocities than older, population II stars. The latter have elliptical orbits that are inclined to the plane of the galaxy.<ref>{{cite journal
 | last= Johnson | first= Hugh M.
 | title=The Kinematics and Evolution of Population I Stars
 | journal=Publications of the Astronomical Society of the Pacific | date=1957 | volume=69 | issue=406 | page=54
 | bibcode=1957PASP...69...54J
 | doi=10.1086/127012| doi-access=free}}</ref> A comparison of the kinematics of nearby stars has allowed astronomers to trace their origin to common points in giant molecular clouds; such groups with common points of origin are referred to as [[stellar association]]s.<ref>{{cite journal |last1=Elmegreen |first1=B. |last2=Efremov |first2=Y. N. |date=1999 |title=The Formation of Star Clusters |url=http://www.americanscientist.org/template/AssetDetail/assetid/15714/page/1 |journal=American Scientist |volume=86 |issue=3 |page=264 |bibcode=1998AmSci..86..264E |doi=10.1511/1998.3.264 |s2cid=209833510 |archive-url=https://web.archive.org/web/20050323072521/http://www.americanscientist.org/template/AssetDetail/assetid/15714/page/1 |archive-date=2005-03-23 |access-date=2006-08-23}}</ref>