newenvironment : synonym for an existing environment

Question

As in this example Redefine environment to be a synonym for another I want to have a synonym for an existing environment. So I created bigSystEquation being an align* environment. (In order to don't have to know that I use align*)

But the code below gives me an error : the error

! LaTeX Error: \begin{align*} on input line 10 ended by \end{bigSystEquation}.

See the LaTeX manual or LaTeX Companion for explanation.
Type  H <return>  for immediate help.
 ...                                              

l.13    \end{bigSystEquation}

And if I change the line 13 by \end{align*} (just curiosity, it has no sense to do so)

! LaTeX Error: \begin{bigSystEquation} on input line 10 ended by \end{document}
.

See the LaTeX manual or LaTeX Companion for explanation.
Type  H <return>  for immediate help.
 ...                                              

l.14 \end{document}

Here is the code

\documentclass[a4paper]{article}
\usepackage{amssymb}
\usepackage{amsmath}
\allowdisplaybreaks
\newenvironment{bigSystEquation}{\begin{align*}}{\end{align*}}

\begin{document}
    \begin{bigSystEquation}
        a &= b\\
        c &= d \\
    \end{bigSystEquation}
\end{document}