## New moon |

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In **new moon** is the first ^{[1]} At this phase, the lunar disk is not visible to the ^{[note 1]}

The original meaning of the term *new moon*, which is still sometimes used in non-astronomical contexts, was the first visible crescent of the Moon, after ^{[2]} This crescent Moon is briefly visible when low above the western

A **lunation** or ^{[3]} In a

- determining new moons: an approximate formula
- lunation number
- lunar calendars
- see also
- notes
- references
- external links

This article
contains . (January 2018) |

The length of a lunation is about 29.53 days. Its precise duration is linked to many phenomena in nature, such as the variation between

where *N* is an integer, starting with 0 for the first new moon in the year 2000, and that is incremented by 1 for each successive synodic month; and the result *d* is the number of days (and fractions) since 2000-01-01 00:00:00 reckoned in the time scale known as

To obtain this moment expressed in *UT*, world clock time), add the result of following approximate correction to the result *d* obtained above:

- days

Periodic perturbations change the time of true conjunction from these mean values. For all new moons between 1601 and 2401, the maximum difference is 0.592 days = 14h13m in either direction. The duration of a lunation (*i.e.* the time from new moon to the next new moon) varies in this period between 29.272 and 29.833 days, i.e. −0.259d = 6h12m shorter, or +0.302d = 7h15m longer than average.^{[4]}^{[5]} This range is smaller than the difference between mean and true conjunction, because during one lunation the periodic terms cannot all change to their maximum opposite value.

See the article on the

The long-term error of the formula is approximately: 1 cy^{2} seconds in TT, and 11 cy^{2} seconds in UT (*cy* is centuries since 2000; see section *Explanation of the formulae* for details.)

The moment of mean conjunction can easily be computed from an expression for the mean ecliptical longitude of the Moon minus the mean ecliptical longitude of the Sun (Delauney parameter *D*). *Astronomical Formulae for Calculators* based on the ephemerides of Brown and Newcomb (ca. 1900); and in his 1st edition of *Astronomical Algorithms*^{[6]} based on the ELP2000-85^{[7]} (the 2nd edition uses ELP2000-82 with improved expressions from Chapront *et al.* in 1998). These are now outdated: Chapront *et al.* (2002)^{[8]} published improved parameters. Also Meeus's formula uses a fractional variable to allow computation of the four main phases, and uses a second variable for the secular terms. For the convenience of the reader, the formula given above is based on Chapront's latest parameters and expressed with a single integer variable, and the following additional terms have been added:

constant term:

- Like Meeus, apply the constant terms of the
aberration of light for the Sun's motion andlight-time correction for the Moon^{[note 2]}to obtain the apparent difference in ecliptical longitudes:

- Sun: +20.496"
^{[9]} - Moon: −0.704"
^{[10]} - Correction in conjunction: −0.000451 days
^{[note 3]}

- For UT: at 1 January 2000,
ΔT (=TT −UT ) was +63.83 s;^{[note 4]}hence the correction for the clock time UT = TT − ΔT of the conjunction is:

- −0.000739 days.

quadratic term:

- In ELP2000–85 (see Chapront
*et alii*1988),*D*has a quadratic term of −5.8681"T^{2}; expressed in lunations N, this yields a correction of +87.403×10^{–12}N^{2}^{[note 5]}days to the time of conjunction. The term includes atidal contribution of 0.5×(−23.8946 "/cy^{2}). The most current estimate from Lunar Laser Ranging for the acceleration is (see Chapront*et alii*2002): (−25.858 ±0.003)"/cy^{2}. Therefore, the new quadratic term of*D*is = -6.8498"T^{2}.^{[note 6]}Indeed, the polynomial provided by Chapront*et alii*(2002) provides the same value (their Table 4). This translates to a correction of +14.622×10^{−12}N^{2}days to the time of conjunction; the quadratic term now is:

- +102.026×10
^{−12}N^{2}days.

- For UT: analysis of historical observations shows that ΔT has a long-term increase of +31 s/cy
^{2}.^{[11]}Converted to days and lunations,^{[note 7]}the correction from ET to UT becomes:

- −235×10
^{−12}N^{2}days.

The theoretical tidal contribution to ΔT is about +42 s/cy^{2}^{[12]} the smaller observed value is thought to be mostly due to changes in the shape of the Earth.^{[13]} Because the discrepancy is not fully explained, uncertainty of our prediction of UT (rotation angle of the Earth) may be as large as the difference between these values: 11 s/cy^{2}. The error in the position of the Moon itself is only maybe 0.5"/cy^{2},^{[note 8]} or (because the apparent mean angular velocity of the Moon is about 0.5"/s), 1 s/cy^{2} in the time of conjunction with the Sun.

Other Languages

العربية: محاق

বাংলা: অমাবস্যা

беларуская: Маладзік

български: Новолуние

català: Lluna nova

čeština: Nov

dansk: Nymåne

Deutsch: Neumond

español: Luna nueva

Esperanto: Novluno

estremeñu: Novicionis

فارسی: ماه نو

français: Nouvelle lune

Frysk: Nijmoanne

한국어: 신월

Bahasa Indonesia: Bulan baru

italiano: Novilunio

עברית: מולד הלבנה

ქართული: ახალმთვარეობა

kaszëbsczi: Nów

Kiswahili: Mwezi mwandamo

Lëtzebuergesch: Neimound

lietuvių: Jaunatis

македонски: Млада месечина

മലയാളം: അമാവാസി

Bahasa Melayu: Anak bulan

Nederlands: Nieuwe maan

नेपाली: औंसी

日本語: 朔

Nordfriisk: Neimuun

norsk: Nymåne

norsk nynorsk: Lunasjon

occitan: Luna novèla

oʻzbekcha/ўзбекча: Yangi oy

Plattdüütsch: Neemaand

polski: Nów

português: Lua nova

Ripoarisch: Neumond

română: Lună nouă

Runa Simi: Killa wañuy

русский: Новолуние

Scots: New muin

slovenčina: Nov (fáza Mesiaca)

suomi: Uusikuu

svenska: Nymåne

Tagalog: Bagong buwan

தமிழ்: அமைவாதை

ไทย: จันทร์ดับ

Türkçe: Yeni ay

українська: Молодик

اردو: ولادت قمر

walon: Tinre lune

粵語: 朔

中文: 新月