https://blog.wongcw.com/2020/07/24/nrao%e6%96%b0%e7%85%a7%e7%89%87%e6%8f%ad%e7%a4%ba%e4%ba%86ngc-4217%e6%bc%a9%e6%b8%a6%e6%98%9f%e7%b3%bb%e7%9a%84%e7%a3%81%e5%a0%b4%e6%9c%89%e5%a4%9a%e7%a7%91%e5%b9%bb/