# Nodal period

The nodal period (or draconic period) of a satellite is the time interval between successive passages of the satellite through either of its orbital nodes, typically the ascending node.wikipedia

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### Orbital period

**periodsynodic periodsynodic**

This type of orbital period applies to artificial satellites, like those that monitor weather on Earth, and natural satellites like the Moon. It is distinct from the sidereal period, which measures the period with respect to reference stars seemingly fixed onto a spherical background, since the location of a satellite's nodes precess over time.

### Satellite

**satellitesartificial satelliteartificial satellites**

The nodal period (or draconic period) of a satellite is the time interval between successive passages of the satellite through either of its orbital nodes, typically the ascending node.

### Orbital node

**Nodeascending nodenodes**

The nodal period (or draconic period) of a satellite is the time interval between successive passages of the satellite through either of its orbital nodes, typically the ascending node.

### Weather satellite

**satellitemeteorological satelliteWeather**

This type of orbital period applies to artificial satellites, like those that monitor weather on Earth, and natural satellites like the Moon.

### Earth

**Earth's surfaceterrestrialworld**

This type of orbital period applies to artificial satellites, like those that monitor weather on Earth, and natural satellites like the Moon.

### Natural satellite

**moonmoonssatellite**

This type of orbital period applies to artificial satellites, like those that monitor weather on Earth, and natural satellites like the Moon.

### Moon

**lunarthe MoonLuna**

### Fixed stars

**fixed starfixedstars**

It is distinct from the sidereal period, which measures the period with respect to reference stars seemingly fixed onto a spherical background, since the location of a satellite's nodes precess over time.

### Celestial sphere

**celestialcelestial hemispherehemisphere**

It is distinct from the sidereal period, which measures the period with respect to reference stars seemingly fixed onto a spherical background, since the location of a satellite's nodes precess over time.

### Nodal precession

**precessnodes precessorbital precession**

It is distinct from the sidereal period, which measures the period with respect to reference stars seemingly fixed onto a spherical background, since the location of a satellite's nodes precess over time.

### Lunar month

**synodic monthsidereal monthanomalistic month**

For example, the nodal period of the Moon is 27.2122 days (one draconic month), while its sidereal period is 27.3217 days (one sidereal month).

### Flattening

**oblatenessellipticityflattened**

The oblate figure of the Earth has important effects of the orbits of near-Earth satellites.

### Figure of the Earth

**curvature of the Earthshape of the EarthEarth's curvature**

The oblate figure of the Earth has important effects of the orbits of near-Earth satellites.

### Geocentric orbit

**GeocentricEarth orbitEarth-orbit**

The oblate figure of the Earth has important effects of the orbits of near-Earth satellites.

### Orbital eccentricity

**eccentricityeccentriceccentricities**

An expression for the nodal period (T n) of a near circular orbit, such that the eccentricity is almost but not equal to zero, is the following:

### Semi-major and semi-minor axes

**semi-major axissemimajor axissemi-major axes**

where a is the semi-major axis, \mu is the gravitational constant, J_2 is a perturbation factor due to the oblateness of the earth, i is the inclination, R is the radius of the earth and \omega is the argument of the perigee.

### Perturbation (astronomy)

**perturbationsperturbationperturbed**

where a is the semi-major axis, \mu is the gravitational constant, J_2 is a perturbation factor due to the oblateness of the earth, i is the inclination, R is the radius of the earth and \omega is the argument of the perigee.

### Orbital inclination

**inclinationinclinedtilted**

where a is the semi-major axis, \mu is the gravitational constant, J_2 is a perturbation factor due to the oblateness of the earth, i is the inclination, R is the radius of the earth and \omega is the argument of the perigee.

### Argument of periapsis

**argument of perihelionargument of perigeeargument of pericenter**

### Registration Convention

**Convention on Registration of Objects Launched into Outer SpaceConvention on Registration of Launched Objects into Outer SpaceConvention on Registration of Objects Launched into Outer Space Objects**

### Lunar node

**nodeNorth Nodelunar nodes**

Because the orbital plane of the Moon precesses in space, the lunar nodes also precess around the ecliptic, completing one revolution (called a draconic or nodal period) in 18.612958 year.

### Lunar precession

**precess18.6 and 8.85 yearslunar apsidal precession**

This is the reason that a draconic month or nodal period (the period the Moon takes to return to the same node in its orbit) is shorter than the sidereal month.

### Lunar standstill

**lunar minor standstilllunisticemaximum southern moon rise**

The Moon's declination also changes, completing a cycle once every lunar nodal period: 27.212 days.

### Molniya (satellite)

**MolniyaMolniya 1Molniya-1**

Similarly, to ensure the ground track repeats every 24 hours the nodal period needed to be half a sidereal day.

### Molniya orbit

**Molniyahighly elliptical orbitMolniya orbit satellite**

However, the oblateness of the Earth also perturbs the right ascension of the ascending node (\Omega), changing the nodal period and causing the ground track to drift over time at the rate shown in equation.