Sections running off page

Question

I have a long list of sections and subsections like so

\chapter{Thin Lenses}
\section*{Aim}
\section*{A. Types of Lenses}
\subsection*{Prediction}
\subsection*{Observation}
\subsection*{Explanation}
\section*{B. Image Formation}
\subsection*{B1. The lens and the image and the object position}
\subsection*{B2. Partial lens}
\subsection*{B3. Eyeballing the image}
\section*{C. Focal Length of a Converging Lens}
\subsubsection*{Question 1}
\subsection*{C1. Estimating the focal length: Eyeballing the image}
\subsubsection*{Prediction}
\subsubsection*{Observation}
\subsubsection*{Explanation}
\subsubsection*{Focal length estimation 1}
\subsection*{C2. Estimating the focal length: Parallel rays}
\subsubsection*{Prediction}
\subsubsection*{Observation}
\subsubsection*{Explanation}
\subsubsection*{Focal length estimation 2}
\subsubsection*{Question 2}

etc. which just run off the bottom of the first page and disappear. Why is this? It doesn't happen if I include some text in the sections.