getsurei （月齢）

now := time.Now()
switch getsurei.Gessou(now) {
case NewMoon:
  fmt.Println("hiding out all night")
case FirstQuarter:
  fmt.Println("still not full")
case FullMoon:
  fmt.Println("bold and bright")
case LastQuarter:
  fmt.Println("whisper goodbye with a quiet thrill")
}

age := getsurei.Getsurei(now)
fmt.Printf("%f days since the new moon\n", age)

fullmoon := getsurei.Next(getsurei.FullMoon, now)
fmt.Printf("net full moon: %s\n", fullmoon.Format("2006.01.02)")

$ date
Mon Jan 27 17:27:07 JST 2025
$ getsurei
下弦の月
$ getsurei 2025.01.01
新月