\begin{table}%t2
%\centering
\par
\caption {\label{SSN}Correlation between $L$-band flux density and sunspot number (SSN).           } %\centerline
 {
\begin{tabular}{c c c c}        
\hline\hline   
\noalign{\smallskip}
Date & $L$-Band Flux   & SSN & Reference \\
     &         Density &     &   \\
 & mJy & & \\
\hline                        % inserts single horizontal line
  May 1975 (Kitt Peak) & $\leq$10 & 9~$\pm$~11.1 & [1] \\
  May 1997 (ISOPHOT) & 7 & 18.5~$\pm$~13.4 & [2]\\
  Aug 2002 (VLT) & 20 & 116.4~$\pm$~36.3 & [3]\\
  May 2007 (AKARI) & 5.5 & 11.7~$\pm$~6.8 & [4] \\
\hline                                 
\end{tabular}}
\tablefoot {$L$-band flux densities were estimated from the spectra shown in the relevant publications [1] \citet{77pilcher}, [2] \citet{00encrenaz}, [3] \citet{03feuchtgruber} and [4] This work.   Monthly averages and standard deviation for SSN were taken from the International Sunspot Numbers, compiled by the Solar Influences Data Analysis Center in Belgium (\protect\url{http://solarscience.msfc.nasa.gov/greenwch/spot_num.txt}).}
\end{table}