TikZ-PGF Diagrams – How to Draw Thales Circle with Marked Angles

Question

I want to draw this picture:

This is what I have so far:

\documentclass[12pt]{article}
\usepackage[utf8]{inputenc}
\usepackage{tikz}

\begin{document}

\begin{center}

\begin{tikzpicture}
\coordinate (S) at (0,0); %does nothing
\draw (0,0) circle (2cm);
\draw (-2,0)  -- (2,0);

\end{tikzpicture}

\end{center}

\end{document}

I'm sorry, I'm new to tikz, so sorry for my basic question. Can anyone please help?

Answer 1

Here is a solution with pstricks:

\documentclass[border=10pt, svgnames]{standalone}
\usepackage{pst-eucl}

\begin{document}

\begin{pspicture}(-2,-2)(2,2)
\psset{linejoin=1}
\pnodes(-2,0){A}(2,0){B}(2;120){C}(0,0){S} \uput[dr](S){$S$}
\psset{LabelSep=0.4, MarkAngleRadius=0.6, linecolor=LightSeaGreen}
\everypsbox{\small\color{LightSeaGreen}}
\pstMarkAngle{S}{A}{C}{$\color{LightSeaGreen}\alpha$}
\pstMarkAngle{A}{C}{S}{$\color{LightSeaGreen}\alpha$}
\psset{linecolor=DeepSkyBlue, MarkAngleRadius=0.9, LabelSep=0.7}
\everypsbox{\small\color{DeepSkyBlue}}
\pstMarkAngle{S}{C}{B}{$\beta$}
\pstMarkAngle{C}{B}{S}{$\beta$}
\psset{linecolor=black}
\pstCircleAB{A}{B}
\psline(A)(C)(B)(A)\psline(C)(S)
\end{pspicture}

\end{document}