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\item Convection  \end{itemize}  One chapter will thus be dedicated to each of these subjects in this review. We have also dedicated a chapter to the discussion of the 'Solar Analogs' and 'The Sun in Time' projects \citep{Cayrel_de_Strobel_1996, G_del_2007}. \citep{Cayrel_de_Strobel_1996,G_del_2007}.  This review will be based on \cite{Hall_2008} and should start by discussing the main ideas in this review. 
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\item Observation of degeneration of spectral lines due to the Zeeman effect \cite{Zeeman_1897}  \end{itemize}  To our knowledge the first observations of emission in Ca II H \& K lines in solar-like stars were done by \cite{Eberhard_1913} and they noted that this emission was similar to what was seen in sun-spots. In fact they also speculated \textit{It remains to be shown whether the smission lines of the star have a possible variation in intensity analogous to the sun-spot period}. This glove was taken up by \cite{Wilson_1968, Wilson_1978} \cite{Wilson_1968,Wilson_1978}  who measured variability in the chromospheric emission from 91 main-sequence stars (F2 to M2) over the length of a solar cycle. These observation revealed that cyclical variations occur with periods ranging from about 7 years to probably at least twice as long. These observations were updated by \cite{Duncan_1991}, who also introduced the canonical S-index at a measurement of the chromospheric emission. The last big update from what is know known as the Mount Wilson project was \cite{Baliunas_1995} and a smaller update of 35 stars was presented in \cite{Radick_1998}, which also made the first connection between the observations at Mount Wilson and Lowell observatories. The observations at the Mount Wilson Observatory were terminated in 2003, but complementary observations of the  97 stars began in 1996 at the Lowell Observatory and are still ongoing \cite{Hall_2007, Hall_2009}. \cite{Hall_2007,Hall_2009}.  Unfortunately, these two sets of observations have never been combined. In fact non of the Mount Wilson observations are public and \cite{Baliunas_1995} only include observations up to 1992, so in somewhere a decade of unpublished observations is laying around just waiting to me published. The results from \cite{Baliunas_1995} can be summerise as follows: out of 112 stars with spectral class between F2 and M2 including the Sun 52 showed cycles with periods between 2.5 to 25 years, 29 showed variability, but no cycles and 31 showed no variability or only a linear trend. For stars with spectra class between G0 to K5 V a pattern of changes in the rotation and chromospheric activity on an evolutionary timescale was indetified. This pattern suggested that these stars could be separated into three distinct groups: 1) stars younger than 1 Gyr that were characterized by fast rotation and high average activity levels. These stars often show large variability, but rarly cycles; 2) stars of intermediate age that were characterized by moderate rotation rates and activity levels. These stars often had shooth cycles and 3) stars as old as the Sun or older that were characterized by slow rotation and low activity levels. Some of these stars showed smooth cycles and some showed flat activity levels.  
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A number studies have also searched and found indication of stellar cycles in stars later than F. \cite{2015A&A...583A.134F} tried to measure rotation periods in 16 FGK main-sequence stars using observations from CoRoT. Periods between 33 and 650 days are found. Though simulations predict that only half of these cycle period should be true, it is remarkable to see the nice relation between rotation and cycle period, including the identification of a active and an inactive branch. \cite{2015ApJS..221...18H} analyzed to G-type stars, with rotation periods of 6.0 and 14.7 days and found indication of activity cycles of 1.3 and 2.5 years respectively. Again, this is shorter than the periods found by \cite{Baliunas_1995} and here both studies are looking at Sun-like stars. By comparing the photometric variability observed in these two stars with the Sun, \cite{2015ApJS..221...18H} arrives at another very interesting conclusion, i.e. that the rotational modulations of the light curves observed by {\it Kepler} for these two stars are caused by bright faculae and not dark spots.  A number of studies have been published analyzing photometric variability in {\it Kepler} light curves \citep{2010ApJ...713L.155B, 011AJ....141...20B, 2013Natur.500..427B, 2014ApJ...788L...9B, 2011AJ....141...50W, 2011AJ....141...50W, 2015arXiv15120} \citep{2010ApJ...713L.155B,011AJ....141...20B,2013Natur.500..427B,2014ApJ...788L...9B,2011AJ....141...50W,2011AJ....141...50W,2015arXiv15120}  \cite{2011AJ....141...20B} \cite{2010ApJ...713L.155B} \cite{2011AJ....141...50W}, \cite{2013MNRAS.436.1883W}, \cite{2015arXiv151203454B}, \cite{2014ApJ...788L...9B}, \cite{2013Natur.500..427B}, without attributing this variability to stellar cycles. We will come back to these studies in the next sections. 
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\section{Rotation}  The study of stellar rotation was pioneered Robert P. Kraft in a series of papers \cite{Kraft_1965a, Kraft_1965b, Anderson_1966, Kraft_1967a, Kraft_1967b}. \cite{Kraft_1965a,Kraft_1965b,Anderson_1966,Kraft_1967a,Kraft_1967b}.  These observations, together with the early observation from Odie Wilson led to the famous Skumanich spin-down law \cite{Skumanich_1972}. Recently,