New moon

For other uses, see New moon (disambiguation).
A simulated image of the traditionally defined new Moon: the earliest visible waxing crescent (lower right), which signals the start of a new month in many lunar and lunisolar calendars.[1] At new moon, mostly earthlight illuminates the near side of the Moon.[a]
As the Earth revolves around the Sun, approximate axial parallelism of the Moon's orbital plane (tilted five degrees to the Earth's orbital plane) results in the revolution of the lunar nodes relative to the Earth. This causes an eclipse season approximately every six months, in which a solar eclipse can occur at the new moon phase.

In astronomy, the new moon is the first lunar phase, when the Moon and Sun have the same ecliptic longitude.[2] At this phase, the lunar disk is not visible to the naked eye, except when it is silhouetted against the Sun during a solar eclipse.

The original meaning of the term 'new moon', which is still sometimes used in calendrical, non-astronomical contexts, is the first visible crescent of the Moon after conjunction with the Sun.[3] This thin waxing crescent is briefly and faintly visible as the Moon gets lower in the western sky after sunset. The precise time and even the date of the appearance of the new moon by this definition will be influenced by the geographical location of the observer. The first crescent marks the beginning of the month in the Islamic calendar[4] and in some lunisolar calendars such as the Hebrew calendar. In the Chinese calendar, the beginning of the month is marked by the last visible crescent of a waning Moon.

The astronomical new moon occurs by definition at the moment of conjunction in ecliptical longitude with the Sun when the Moon is invisible from the Earth. This moment is unique and does not depend on location, and in certain circumstances, it coincides with a solar eclipse.

A lunation, or synodic month, is the period from one new moon to the next. At the J2000.0 epoch, the average length of a lunation is 29.53059 days (or 29 days, 12 hours, 44 minutes, and 3 seconds).[5] However, the length of any one synodic month can vary from 29.26 to 29.80 days (12.96 hours) due to the perturbing effects of the Sun's gravity on the Moon's eccentric orbit.[6]

  1. ^ "New Moon". Flickr. NASA/GSFC. 15 June 2011.
  2. ^ Meeus 1991, p. 319.
  3. ^ "new moon". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
  4. ^ Islamic Crescents' Observation Project, Visibility of Muharram Crescent 1432 AH Archived 10 May 2012 at the Wayback Machine; seen on 6 December in Algeria, Iran, Saudi Arabia, South Africa.
  5. ^ Seidelmann 1992, p. 576.
  6. ^ Espenak, Fred. "Eclipses and the Moon's Orbit". NASA Eclipse Web Site. NASA. Retrieved 11 December 2016.


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