\begin{table}%t1
%\centering
\par
\caption{\label{tabtime}UT at the start of the first of each pair of exposures.}
\small \begin{tabular}{c c c c c}
\hline\hline
Field  &  \multicolumn{4}{c}{Night} \\
  &  12  &  13  &  14  &  15 \\
\hline
NGC~5986  &  1:18  &  23:19  &  3:00  &  3:00 \\
 &  3:23  &    &    &   \\
%\hline
M~80a  &  --  &  6:20  &  23:27  &  4:30 \\
 &    &    &  0:53  &   \\
%\hline
M~80b  &  --  &  --  &  4:31  &  23:32 \\
 &    &    &    &  0:57 \\
\hline
\end{tabular}
\end{table}