\begin{table}%t1
%\centering
\par
\caption{Observational details.\label{tab1} }             
\begin{tabular}{c c c }        % centered columns (4 columns)
\hline\hline                 % inserts double horizontal lines
Setup & Central & Date(s) \\
& frequencies (GHz) & \\
\hline                        % inserts single horizontal line
1 & 230.154, 230.922 & 08/15/03, 05/12/04, 05/13/04 \\
2 & 228.618, 229.386 & 08/15/03, 05/12/04\\
3 & 231.690, 232.458 & 09/01/03, 05/13/04\\
4 & 227.082, 227.850 & 05/12/04 \\	    
5 & 233.226, 233.994 & 05/13/04 \\
\hline                                   %inserts single line
\end{tabular}
\end{table}