astronomy/jsdoc2md/js.hbs

# Astronomy Engine (JavaScript)
This is the complete programming reference for the JavaScript version
of Astronomy Engine. It supports client side programming
in the browser and backend use of [Node.js](https://nodejs.org).
Other programming languages are supported also.
See the [home page](https://github.com/cosinekitty/astronomy) for more info.

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## Quick Start
To get started quickly, here are some [browser scripting examples](../../demo/browser/)
and some [Node.js examples](../../demo/nodejs/).

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## Topic Index

### Position of Sun, Moon, and planets

| Function | Description |
| -------- | ----------- |
| [HelioVector](#Astronomy.HelioVector) | Calculates vector with respect to the center of the Sun.   |
| [GeoVector](#Astronomy.GeoVector)     | Calculates vector with respect to the center of the Earth. |
| [Equator](#Astronomy.Equator)         | Calculates right ascension and declination. |
| [Ecliptic](#Astronomy.Ecliptic)       | Calculates ecliptic latitude, longitude, and Cartesian coordinates. |
| [Horizon](#Astronomy.Horizon)         | Calculates horizontal coordinates (azimuth, altitude) for a given observer on the Earth. |

### Rise, set, and culmination times

| Function | Description |
| -------- | ----------- |
| [SearchRiseSet](#Astronomy.SearchRiseSet) | Finds time of rise or set for a body as seen by an observer on the Earth. |
| [SearchHourAngle](#Astronomy.SearchHourAngle) | Finds when body reaches a given hour angle for an observer on the Earth. Hour angle = 0 finds culmination, the highest point in the sky. |

### Moon phases

| Function | Description |
| -------- | ----------- |
| [MoonPhase](#Astronomy.MoonPhase) | Determines the Moon's phase expressed as an ecliptic longitude. |
| [SearchMoonQuarter](#Astronomy.SearchMoonQuarter) | Find the first quarter moon phase after a given date and time. |
| [NextMoonQuarter](#Astronomy.NextMoonQuarter) | Find the next quarter moon phase after a previous one that has been found. |

### Lunar perigee and apogee

| Function | Description |
| -------- | ----------- |
| [SearchLunarApsis](#Astronomy.SearchLunarApsis) | Finds the next perigee or apogee of the Moon after a specified date. |
| [NextLunarApsis](#Astronomy.NextLunarApsis) | Given an already-found apsis, find the next perigee or apogee of the Moon. |

### Visual magnitude and elongation

| Function | Description |
| -------- | ----------- |
| [Illumination](#Astronomy.Illumination) | Calculates visual magnitude and phase angle of bodies as seen from the Earth. |
| [SearchPeakMagnitude](#Astronomy.SearchPeakMagnitude) | Searches for the date and time Venus will next appear brightest as seen from the Earth. |
| [AngleFromSun](#Astronomy.AngleFromSun) | Returns full angle seen from Earth between body and Sun. |
| [Elongation](#Astronomy.Elongation) | Calculates ecliptic longitude angle between a body and the Sun, as seen from the Earth. |
| [SearchMaxElongation](#Astronomy.SearchMaxElongation) | Searches for the next maximum elongation event for Mercury or Venus that occurs after the given date. |

### Oppositions and conjunctions

| Function | Description |
| -------- | ----------- |
| [SearchRelativeLongitude](#Astronomy.SearchRelativeLongitude) | Find oppositions and conjunctions of planets. |

### Equinoxes and solstices

| Function | Description |
| -------- | ----------- |
| [Seasons](#Astronomy.Seasons) | Finds the equinoxes and solstices for a given calendar year. |

### Coordinate transforms

The following four orientation systems are supported.
Astronomy Engine can convert a vector from any of these orientations to any of the others.
It also allows converting from a vector to spherical (angular) coordinates and back,
within a given orientation. Note the 3-letter codes for each of the orientation systems;
these are used in function and type names.

- **EQJ = Equatorial J2000**: Uses the Earth's equator on January 1, 2000, at noon UTC.
- **EQD = Equator of-date**: Uses the Earth's equator on a given date and time, adjusted for precession and nutation.
- **ECL = Ecliptic**: Uses the mean plane of the Earth's orbit around the Sun. The x-axis is referenced against the J2000 equinox.
- **HOR = Horizontal**: Uses the viewpoint of an observer at a specific location on the Earth at a given date and time.

| Function | Description |
| -------- | ----------- |
| [RotateVector](#Astronomy.RotateVector) | Applies a rotation matrix to a vector, yielding a vector in another orientation system. |
| [InverseRotation](#Astronomy.InverseRotation) | Given a rotation matrix, finds the inverse rotation matrix that does the opposite transformation. |
| [CombineRotation](#Astronomy.CombineRotation) | Given two rotation matrices, returns a rotation matrix that combines them into a net transformation. |
| [VectorFromSphere](#Astronomy.VectorFromSphere) | Converts spherical coordinates to Cartesian coordinates. |
| [SphereFromVector](#Astronomy.SphereFromVector) | Converts Cartesian coordinates to spherical coordinates. |
| [VectorFromEquator](#Astronomy.VectorFromEquator) | Given angular equatorial coordinates, calculates equatorial vector. |
| [EquatorFromVector](#Astronomy.EquatorFromVector) | Given an equatorial vector, calculates equatorial angular coordinates. |
| [VectorFromHorizon](#Astronomy.VectorFromHorizon) | Given apparent angular horizontal coordinates, calculates horizontal vector. |
| [HorizonFromVector](#Astronomy.HorizonFromVector) | Given a vector in horizontal orientation, calculates horizontal angular coordinates. |
| [Rotation_EQD_EQJ](#Astronomy.Rotation_EQD_EQJ) | Calculates a rotation matrix from equatorial of-date (EQD) to equatorial J2000 (EQJ). |
| [Rotation_EQD_ECL](#Astronomy.Rotation_EQD_ECL) | Calculates a rotation matrix from equatorial of-date (EQD) to ecliptic J2000 (ECL). |
| [Rotation_EQD_HOR](#Astronomy.Rotation_EQD_HOR) | Calculates a rotation matrix from equatorial of-date (EQD) to horizontal (HOR). |
| [Rotation_EQJ_EQD](#Astronomy.Rotation_EQJ_EQD) | Calculates a rotation matrix from equatorial J2000 (EQJ) to equatorial of-date (EQD). |
| [Rotation_EQJ_ECL](#Astronomy.Rotation_EQJ_ECL) | Calculates a rotation matrix from equatorial J2000 (EQJ) to ecliptic J2000 (ECL). |
| [Rotation_EQJ_HOR](#Astronomy.Rotation_EQJ_HOR) | Calculates a rotation matrix from equatorial J2000 (EQJ) to horizontal (HOR). |
| [Rotation_ECL_EQD](#Astronomy.Rotation_ECL_EQD) | Calculates a rotation matrix from ecliptic J2000 (ECL) to equatorial of-date (EQD). |
| [Rotation_ECL_EQJ](#Astronomy.Rotation_ECL_EQJ) | Calculates a rotation matrix from ecliptic J2000 (ECL) to equatorial J2000 (EQJ). |
| [Rotation_ECL_HOR](#Astronomy.Rotation_ECL_HOR) | Calculates a rotation matrix from ecliptic J2000 (ECL) to horizontal (HOR). |
| [Rotation_HOR_EQD](#Astronomy.Rotation_HOR_EQD) | Calculates a rotation matrix from horizontal (HOR) to equatorial of-date (EQD). |
| [Rotation_HOR_EQJ](#Astronomy.Rotation_HOR_EQJ) | Calculates a rotation matrix from horizontal (HOR) to J2000 equatorial (EQJ). |
| [Rotation_HOR_ECL](#Astronomy.Rotation_HOR_ECL) | Calculates a rotation matrix from horizontal (HOR) to ecliptic J2000 (ECL). |

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## API Reference

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