new moon; first day of the lunar month
Refers to the astronomical new moon when the moon is not visible, or the first day of the lunar calendar month.
Tonight is the new moon, so the moon is completely invisible.
In the old lunar calendar, the day of the new moon was the start of the month.
Sometimes used loosely for a thin crescent moon, though 三日月 is the more precise term. This usage is less common and may be considered non-standard.
See also: 三日月
A thin crescent moon hung in the sky.
満月 is the fully illuminated full moon, while 新月 is the new moon when it is invisible from Earth.
新月 is the new moon, the direct lunar-phase opposite of 望月, the full moon.
From 新 (new) + 月 (moon). The reading しんげつ is the on'yomi (Sino-Japanese) reading of the characters.