Editing Cepheid variable (section)

=== Classical Cepheids ===
{{Main|Classical Cepheid variable}}
[[File:Delta Cephei lightcurve.jpg|thumb|[[Light curve]] of [[Delta Cephei]], the prototype of classical cepheids, showing the regular variations produced by intrinsic stellar pulsations]]
Classical Cepheids (also known as Population I Cepheids, type I Cepheids, or Delta Cepheid variables) undergo pulsations with very regular periods on the order of days to months. Classical Cepheids are [[Population I]] [[variable star]]s which are 4–20 times more massive than the Sun,<ref name=turner96>{{cite journal |bibcode=1996JRASC..90...82T |title=The Progenitors of Classical Cepheid Variables |author1=Turner, David G. |volume=90 |date=1996 |pages=82 |journal=[[Journal of the Royal Astronomical Society of Canada]]}}</ref> and up to 100,000 times more luminous.<ref name=turner10>{{cite journal |arxiv=0912.4864 |bibcode=2010Ap&SS.326..219T |doi=10.1007/s10509-009-0258-5 |title=The PL calibration for Milky Way Cepheids and its implications for the distance scale |date=2010 |last1=Turner |first1=David G. |journal=[[Astrophysics and Space Science]] |volume=326 |issue=2 |pages=219–231 |s2cid=119264970 }}</ref> These Cepheids are yellow bright giants and supergiants of [[spectral classification|spectral class]] F6 – K2 and their radii change by (~25% for the longer-period [[HD 84810|I Carinae]]) millions of kilometers during a pulsation cycle.<ref>{{cite journal |bibcode=1957MNRAS.117...85R |title=Radius variation and population type of cepheid variables |author1=Rodgers, A. W. |volume=117 |date=1957 |pages=85–94 |journal=[[Monthly Notices of the Royal Astronomical Society]] |doi=10.1093/mnras/117.1.85|doi-access=free }}</ref>

Classical Cepheids are used to determine distances to galaxies within the [[Local Group]] and beyond, and are a means by which the [[Hubble constant]] can be established.<ref name=freedman2001>{{cite journal |arxiv=astro.ph/0012376 |bibcode=2001ApJ...553...47F |doi=10.1086/320638 |title=Final Results from the ''Hubble Space Telescope'' Key Project to Measure the Hubble Constant |date=2001 |last1=Freedman |first1=Wendy L. |last2=Madore |first2=Barry F. |last3=Gibson |first3=Brad K. |last4=Ferrarese |first4=Laura |last5=Kelson |first5=Daniel D. |last6=Sakai |first6=Shoko |last7=Mould |first7=Jeremy R. |last8=Kennicutt, Jr. |first8=Robert C. |last9=Ford |first9=Holland C. |last10=Graham |first10=John A. |last11=Huchra |first11=John P. |last12=Hughes |first12=Shaun M. G. |last13=Illingworth |first13=Garth D. |last14=Macri |first14=Lucas M. |last15=Stetson |first15=Peter B. |journal=[[The Astrophysical Journal]] |volume=553 |issue=1 |pages=47–72 |s2cid=119097691 }}</ref><ref name="tammannsandage2008" /><ref name=freedman2010>{{cite journal |arxiv=1004.1856 |bibcode=2010ARA&A..48..673F |title=The Hubble Constant |author1=Freedman, Wendy L. |author2=Madore, Barry F. |volume=48 |date=2010 |pages=673–710 |journal=[[Annual Review of Astronomy and Astrophysics]] |doi=10.1146/annurev-astro-082708-101829 |s2cid=13909389 }}</ref><ref name="ngeow2006" /><ref name="macririess2009" /> Classical Cepheids have also been used to clarify many characteristics of the Milky Way galaxy, such as the Sun's height above the galactic plane and the Galaxy's local spiral structure.<ref name=majaess2009>{{cite journal |arxiv=0903.4206 |bibcode=2009MNRAS.398..263M |doi=10.1111/j.1365-2966.2009.15096.x |title=Characteristics of the Galaxy according to Cepheids |date=2009 |last1=Majaess |first1=D. J. |last2=Turner |first2=D. G. |last3=Lane |first3=D. J. |journal=[[Monthly Notices of the Royal Astronomical Society]] |volume=398 |issue=1 |pages=263–270 |doi-access=free |s2cid=14316644 }}</ref>

A group of classical Cepheids with small amplitudes and [[sinusoidal]] light curves are often separated out as Small Amplitude Cepheids or s-Cepheids, many of them pulsating in the first overtone.