# Plane of reference

**reference planeplaneplanes**

In celestial mechanics, the plane of reference (or reference plane) is the plane used to define orbital elements (positions).wikipedia

34 Related Articles

### Orbital inclination

**inclinationinclinedtilted**

The two main orbital elements that are measured with respect to the plane of reference are the inclination and the longitude of the ascending node.

It is expressed as the angle between a reference plane and the orbital plane or axis of direction of the orbiting object.

### Longitude of the ascending node

**right ascension of the ascending nodelongitude of ascending nodenode**

The two main orbital elements that are measured with respect to the plane of reference are the inclination and the longitude of the ascending node.

### Ecliptic

**ecliptical orbitsecliptic planeplane of the ecliptic**

This plane of reference is coplanar with Earth's orbit around the Sun (and hence the Sun's apparent path around Earth).

### Celestial equator

**equatorialequatorial planeequatorial sky**

This plane of reference bases the equatorial coordinate system.

### Fundamental plane (spherical coordinates)

**fundamental planefundamental planes**

The fundamental plane in a spherical coordinate system is a plane of reference that divides the sphere into two hemispheres.

### Celestial sphere

**celestialcelestial hemispherehemisphere**

Certain reference lines and planes on Earth, when projected onto the celestial sphere, form the bases of the reference systems.

### Celestial mechanics

**celestialcelestial dynamicscelestial mechanician**

In celestial mechanics, the plane of reference (or reference plane) is the plane used to define orbital elements (positions).

### Orbital elements

**orbital parametersorbital elementKeplerian elements**

In celestial mechanics, the plane of reference (or reference plane) is the plane used to define orbital elements (positions).

### Longitude

**WestlongitudinalE**

On the plane of reference, a zero-point must be defined from which the angles of longitude are measured.

### Hour circle

This is usually defined as the point on the celestial sphere where the plane crosses the prime hour circle (the hour circle occupied by the First Point of Aries), also known as the equinox.

### First Point of Aries

**sun passes into the constellation Aries**

This is usually defined as the point on the celestial sphere where the plane crosses the prime hour circle (the hour circle occupied by the First Point of Aries), also known as the equinox.

### Equinox

**autumnal equinoxautumn equinoxequinoxes**

This is usually defined as the point on the celestial sphere where the plane crosses the prime hour circle (the hour circle occupied by the First Point of Aries), also known as the equinox.

### Invariable plane

**common orbital alignmentinvariable plane of the Solar System“invariable” axis**

### Semi-major and semi-minor axes

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

### Lunar precession

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

Lunar precession is the change in orientation of the lunar rotational axis with respect to a reference plane, following the normal rules of precession followed by spinning objects.

### Azimuth

**azimuthalazimuthal angleazimuth angle**

The vector from an observer (origin) to a point of interest is projected perpendicularly onto a reference plane; the angle between the projected vector and a reference vector on the reference plane is called the azimuth.

### Orbital node

**Nodeascending nodenodes**

An orbital node is either of the two points where an orbit intersects a plane of reference to which it is inclined.

### Normalhöhennull

**NHNsea level (NHN)sea level**

In geographical terms, NHN is the reference plane for the normal height of a topographical eminence height above mean sea level used in the 1992 German Mean Height Reference System (Deutsches Haupthöhennetz).

### Epoch (astronomy)

**J2000J2000.0epoch**

These time-varying astronomical quantities might include, for example, the mean longitude or mean anomaly of a body, the node of its orbit relative to a reference plane, the direction of the apogee or aphelion of its orbit, or the size of the major axis of its orbit.

### Non-inclined orbit

**equatorial orbitequatorialEcliptic orbit**

A non-inclined orbit is an orbit coplanar with a plane of reference.

### Orbital plane (astronomy)

**orbital planeorbital planesplane of its orbit**

The orbital plane is defined in relation to a reference plane by two parameters: inclination (i) and longitude of the ascending node .

### Bow and warp of semiconductor wafers and substrates

Bow is the deviation of the center point of the median surface of a free, un-clamped wafer from the reference plane, where the reference plane is defined by.