Editing Variable star (section)

====Long period variables====
{{Main|Long period variable}}

The long period variables are cool evolved stars that pulsate with periods in the range of weeks to several years.

=====Mira variables=====
[[File:Chi Cygni light curve.png|thumb|[[Light curve]] of [[Mira variable]] [[χ Cygni]]]]
{{Main|Mira variable}}

Mira variables are [[Asymptotic giant branch]] (AGB) red giants. Over periods of many months they fade and brighten by between 2.5 and 11 [[apparent magnitude|magnitude]]s, a 6 fold to 30,000 fold change in luminosity. [[Mira]] itself, also known as Omicron Ceti (ο Cet), varies in brightness from almost 2nd magnitude to as faint as 10th magnitude with a period of roughly 332 days. The very large visual amplitudes are mainly due to the shifting of energy output between visual and infra-red as the temperature of the star changes. In a few cases, Mira variables show dramatic period changes over a period of decades, thought to be related to the thermal pulsing cycle of the most advanced AGB stars.

=====Semiregular variables=====
{{Main|Semiregular variable}}

These are [[red giants]] or [[red supergiant|supergiants]]. Semiregular variables may show a definite period on occasion, but more often show less well-defined variations that can sometimes be resolved into multiple periods. A well-known example of a semiregular variable is [[Betelgeuse]], which varies from about magnitudes +0.2 to +1.2 (a factor 2.5 change in luminosity). At least some of the semi-regular variables are very closely related to Mira variables, possibly the only difference being pulsating in a different harmonic.

=====Slow irregular variables=====
{{Main|Slow irregular variable}}

These are [[red giants]] or [[red supergiant|supergiants]] with little or no detectable periodicity. Some are poorly studied semiregular variables, often with multiple periods, but others may simply be chaotic.

=====Long secondary period variables=====
{{Main|Long-period variable star#Long secondary periods}}
Many variable red giants and supergiants show variations over several hundred to several thousand days. The brightness may change by several magnitudes although it is often much smaller, with the more rapid primary variations are superimposed. The reasons for this type of variation are not clearly understood, being variously ascribed to pulsations, binarity, and stellar rotation.<ref name=messina>{{cite journal|bibcode=2007NewA...12..556M|title=Evidence for the pulsational origin of the Long Secondary Periods: The red supergiant star V424 Lac (HD 216946)|journal=New Astronomy|volume=12|issue=7|pages=556–561|last1=Messina|first1=Sergio|year=2007|doi=10.1016/j.newast.2007.04.002}}</ref><ref>{{cite journal|bibcode=2007ApJ...660.1486S|arxiv=astro-ph/0701463|title=Long Secondary Periods and Binarity in Red Giant Stars|journal=The Astrophysical Journal|volume=660|issue=2|pages=1486–1491|last1=Soszyński|first1=I.|year=2007|doi=10.1086/513012|s2cid=2445038}}</ref><ref>{{cite journal|bibcode=2003ApJ...584.1035O|title=On the Origin of Long Secondary Periods in Semiregular Variables|journal=The Astrophysical Journal|volume=584|issue=2|pages=1035|last1=Olivier|first1=E. A.|last2=Wood|first2=P. R.|year=2003|doi=10.1086/345715|citeseerx=10.1.1.514.3679|s2cid=40373007 }}</ref>