The December New Moon occurs tonight (December 22). With the Moon positioned exactly between the Earth and the sun, it is considered an opportune time of the month for a good view of the objects that are otherwise not visible due to the moonlight.
To astronomers, the phrase “new moon” means when the Moon is “in conjunction” with the Sun as seen from Earth. The dark (unilluminated) portion of the Moon faces almost directly towards us on Earth, so the Moon is not visible to the naked eye. The “dark moon” is invisible from Earth.
The original meaning of “new moon” was when first visible crescent of the Moon is seen. That rather imprecise event is a brief period that happens over the western horizon between sunset and moonset, so the exact time/date of this event is based on your geographical location. Culturally, the first crescent marks the beginning of the month in lunar calendars such as the Muslim calendar, and in lunisolar calendars such as the Hebrew calendar, Hindu calendars, and Buddhist calendar. In the Chinese calendar, the beginning of the month is marked by the dark moon.
These beliefs have also led to the Hindu calendar belief that a new moon can create negative mental changes. The goddess Kali is worshiped on new moon night to relax these fluctuations.
Some Chinese Buddhists keep a vegetarian diet on the new and full moons.
The new moon signifies the start of every Jewish month, and is considered an important date and minor holiday in the Hebrew calendar.