A dark moon describes the Moon

Moon

The Moon is Earth's only known natural satellite,There are a number of near-Earth asteroids including 3753 Cruithne that are co-orbital with Earth: their orbits bring them close to Earth for periods of time but then alter in the long term . These are quasi-satellites and not true moons. For more...

 during that time that it is invisible against the backdrop of the Sun

Sun

The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

 in the sky

Sky

The sky is the part of the atmosphere or outer space visible from the surface of any astronomical object. It is difficult to define precisely for several reasons. During daylight, the sky of Earth has the appearance of a pale blue surface because the air scatters the sunlight. The sky is sometimes...

. The duration of a dark moon is between 1.5 and 3.5 days, depending on the orientation of the Earth and Sun.

In astronomical usage, the new moon

New moon

In astronomical terminology, the new moon is the lunar phase that occurs when the Moon, in its monthly orbital motion around Earth, lies between Earth and the Sun, and is therefore in conjunction with the Sun as seen from Earth...

 occurs in the middle of this period, when the moon and sun are in conjunction. This definition has entered popular usage, so that calendars will typically indicate the date of the "new moon" rather than the "dark moon". However, originally "new moon" referred to the crescent

Lunar phase

A lunar phase or phase of the moon is the appearance of the illuminated portion of the Moon as seen by an observer, usually on Earth. The lunar phases change cyclically as the Moon orbits the Earth, according to the changing relative positions of the Earth, Moon, and Sun...

 on the first night it is visible, one or two days after conjunction. Maritime records from the nineteenth century distinguish the dark moon (no moon) from the new moon (young crescent).

See also

• Lunar phase
  Lunar phase
  A lunar phase or phase of the moon is the appearance of the illuminated portion of the Moon as seen by an observer, usually on Earth. The lunar phases change cyclically as the Moon orbits the Earth, according to the changing relative positions of the Earth, Moon, and Sun...
  
  
• Syzygy (astronomy)
  Syzygy (astronomy)
  In astronomy, a syzygy is a straight line configuration of three celestial bodies in a gravitational system. The word is usually used in reference to the Sun, the Earth and either the Moon or a planet, where the latter is in conjunction or opposition. Solar and lunar eclipses occur at times of...
  
  
• Lilith (moon)
• Black moon
  Black moon
  In astronomy, the term black moon is neither well-known nor frequently used. As a consequence it has no accepted definition, but seems to have occasionally been applied to at least four different situations:-Other names:...