\begin{table}%t1
\caption{\label{table:observation}The observation log.}            
%\centering
 \small                         
\begin{tabular}{c c c c c}        
\hline\hline                
%& & & & \\
Obs.   & Date & Modified   & Off-axis angle & Exposure \\    
period &      & Julian Day & [degrees]    & [ks]      \\  
\hline                       
OB1 & 02 Nov. 2007 13:50 UT--16 Dec. 2007 10:27 UT & 54~406.576--54~450.435 & $ \;$ 2.4--27.6 &      1634 \\
OB2 & 10 Apr. 2008 15:10 UT--30 Apr. 2008 11:15 UT & 54~566.632--54~586.469 &      18.3--15.4 & $ \;$ 893 \\
OB3 & 10 May 2008 17:52 UT--30 Jun. 2008 11:10 UT & 54~596.744--54~647.465 & $ \;$ 4.6--32.7 &      1934 \\
OB4 & 17 Oct. 2008 17:00 UT--01 Dec. 2008 11:37 UT & 54~756.708--54~801.484 &      15.1--18.0 &      1632 \\
\hline                                  
\end{tabular}\vspace*{3mm}
\end{table}