[1] julianday.pdf, , http://fomalhautpsa.sakura.ne.jp/Science/OgawaKiyohiko/julianday.pdf#page=2
[2] メトン周期 - Wikipedia () https://ja.wikipedia.org/wiki/%E3%83%A1%E3%83%88%E3%83%B3%E5%91%A8%E6%9C%9F#%E5%A4%AA%E9%99%BD%E5%91%A8%E6%9C%9F
[3] orbital period | RADIO音楽生活~♪, https://ameblo.jp/radio-duck/entry-10578852178.html