begin{eqnarray}
begin{center}
$
X = ( alpha_i - alpha_0 ) * cos (delta_0) \
Y = delta_i - delta_0qedhere$

end{center}
end{eqnarray}

documentclass{article}
usepackage{amsmath, amsthm}

begin{document}

begin{align*}
X &= ( alpha_i - alpha_0 ) * cos (delta_0) \
Y & = delta_i - delta_0qedhere
end{align*}

end{document}