conjunction (astronomy), first day of month, north
朔 centers on the start of a lunar cycle: the astronomical conjunction when the moon is invisible, marking the first day of the month. The north sense is a less common application, possibly from directional associations in ancient calendars.
朔 combines 屰 (which historically relates to going against or returning) with 月 (moon), suggesting the moon's return to the starting point of its cycle. The exact development of 屰 is uncertain, but the compound points to the new moon conjunction.
The left side 屰 looks like a person turning back, and the right side 月 is the moon. Picture the moon turning back to its invisible starting point at the first day of the month.
For サク, imagine the moon's cycle starting with a sudden 'sack' of darkness: sack -> サク, and the new moon is hidden in that sack.
new moon
Hassaku orange (Citrus hassaku)
first day of the month (in the lunar calendar)
first day of the second month
last and first days of the month
first and fifteenth days of the lunar month (corresponding to new moon and full moon)
synodic month
spring tide
north wind
beginning of the month or the year; New Year's Day; the calendar
1st day of the 4th month of the lunisolar calendar
ceremony where the Emperor would inspect the records of attendance and absence of officials