\begin{table}%t1
 %\centering
\par
 \caption{Observation log.} \label{tab:alldata}
 \begin{tabular}{llll}
 \hline \hline  
 Sequence    & Date and Start time (UT)  & End time  & Exposure   \\
 & (yyyy-mm-dd hh:mm:ss)  & (hh:mm:ss)  &    (s)\\
  \hline  
37~039~001 &   2007-12-21 07:20:40 &    13:32:56 &   1664\\
37~039~002 &   2007-12-30 00:02:31 &    08:21:57 &   5762\\
  \hline
  \end{tabular}
  \end{table}