\begin{table}%t1
    \caption{\label{hegra_observations}Individual periods of \eee\  observations with the
      HEGRA~IACT system. Listed are
      the total observation times and mean zenith angles $\langle \vartheta
      \rangle$. 
      Typically, each night comprises about~1~h of observation time.}
        %\centering
\par
      \begin{tabular}{lccc}
       \hline \hline\noalign{\smallskip}
        Date                     &     Year   &   Obs. Time   &     $\langle \vartheta \rangle$ \\
                                 &            &   [h]         &     [$^\circ$] \\
       \noalign{\smallskip} \hline\noalign{\smallskip}
        July 28--August 2      &     2000   &    8.2        &     40.0 \\
        August 28--September 6 &     2000   &   10.2        &     40.7 \\
        \noalign{\smallskip}\hline\noalign{\smallskip}
         May 18--June 1         &     2001   &   13.0	 &     37.4 \\
        June 22--June 28       &     2001   &   15.5	&     38.1 \\
        July 11--July 22       &     2001   &    8.5	&     38.1 \\
        August 9--August 25    &     2001   &   17.5        &     37.2 \\
        September 6--September 19 &  2001   &   15.0        &     37.3 \\
        October 11--October 21 &     2001   &   19.9        &     40.1 \\
       \noalign{\smallskip} \hline\noalign{\smallskip}
        May 18--May 21         &     2002   &   10.0	&     41.8 \\
        June 3--June 18        &     2002   &   34.4	&     38.5 \\
        July 1--July 18        &     2002   &   18.7	&     39.5 \\
       July 31--August 16     &     2002   &   20.2        &     38.4 \\
   September 3--September 11 &  2002   &    6.3        &	 38.6 \\
        \noalign{\smallskip}\hline\noalign{\smallskip}
        Sum                      &            &  197.4        &     38.8 \\ \hline
      \end{tabular}
   \end{table}