astronomy/csdown/csharp_prefix.md

Astronomy Engine (C#)

This is the complete programming reference for the C# version of Astronomy Engine. Other programming languages are supported. See the home page for more info.

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Quick Start

To include Astronomy Engine in your own C# program, all you need is the file astronomy.cs from this directory.

To get started quickly, here are some examples.

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Contents

• Topic Index
• Constants
• Functions
• Types

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Topic Index

Position of Sun, Moon, and planets

Function	Description
HelioVector	Calculates body position vector with respect to the center of the Sun.
GeoVector	Calculates body position vector with respect to the center of the Earth.
Equator	Calculates right ascension and declination.
EquatorialToEcliptic	Converts J2000 equatorial coordinates to J2000 ecliptic coordinates.
EclipticLongitude	Calculates ecliptic longitude of a body in the J2000 system.
Horizon	Calculates horizontal coordinates (azimuth, altitude) for a given observer on the Earth.
PairLongitude	Calculates the difference in apparent ecliptic longitude between two bodies, as seen from the Earth.
BaryState	Calculates the barycentric position and velocity vectors of the Sun or a planet.

Geographic helper functions

Function	Description
ObserverVector	Calculates a vector from the center of the Earth to an observer on the Earth's surface.
VectorObserver	Calculates the geographic coordinates for a geocentric equatorial vector.

Rise, set, and culmination times

Function	Description
SearchRiseSet	Finds time of rise or set for a body as seen by an observer on the Earth.
SearchAltitude	Finds time when a body reaches a given altitude above or below the horizon. Useful for finding civil, nautical, or astronomical twilight.
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	Determines the Moon's phase expressed as an ecliptic longitude.
SearchMoonPhase	Finds the next instance of the Moon reaching a specific ecliptic longitude separation from the Sun.
SearchMoonQuarter	Finds the first quarter moon phase after a given date and time.
NextMoonQuarter	Finds the next quarter moon phase after a previous one that has been found.

Eclipses and Transits

Function	Description
SearchLunarEclipse	Search for the first lunar eclipse after a given date.
NextLunarEclipse	Continue searching for more lunar eclipses.
SearchGlobalSolarEclipse	Search for the first solar eclipse after a given date that is visible anywhere on the Earth.
NextGlobalSolarEclipse	Continue searching for solar eclipses visible anywhere on the Earth.
SearchLocalSolarEclipse	Search for the first solar eclipse after a given date that is visible at a particular location on the Earth.
NextLocalSolarEclipse	Continue searching for solar eclipses visible at a particular location on the Earth.
SearchTransit	Search for the next transit of Mercury or Venus.
NextTransit	Continue searching for transits of Mercury or Venus.

Lunar perigee and apogee

Function	Description
SearchLunarApsis	Finds the next perigee or apogee of the Moon after a specified date.
NextLunarApsis	Given an already-found apsis, finds the next perigee or apogee of the Moon.

Planet perihelion and aphelion

Function	Description
SearchPlanetApsis	Finds the next perihelion or aphelion of a planet after a specified date.
NextPlanetApsis	Given an already-found apsis, finds the next perihelion or aphelion of a planet.

Visual magnitude and elongation

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

Oppositions and conjunctions

Function	Description
SearchRelativeLongitude	Finds oppositions and conjunctions of planets.

Equinoxes, solstices, and apparent solar motion

Function	Description
SearchSunLongitude	Finds the next time the Sun reaches a specified apparent ecliptic longitude in the true equator of date system.
Seasons	Finds the equinoxes and solstices for a given calendar year.
SunPosition	Calculates the Sun's apparent ecliptic coordinates as seen from the Earth.

Coordinate transforms

The following five 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.
• GAL = Galactic: Based on the IAU 1958 definition of galactic coordinates.

Function	Description
RotateVector	Applies a rotation matrix to a vector, yielding a vector in another orientation system.
InverseRotation	Given a rotation matrix, finds the inverse rotation matrix that does the opposite transformation.
CombineRotation	Given two rotation matrices, returns a rotation matrix that combines them into a net transformation.
IdentityMatrix	Returns a 3x3 identity matrix, which can be used to form other rotation matrices.
Pivot	Transforms a rotation matrix by pivoting it around a given axis by a given angle.
VectorFromSphere	Converts spherical coordinates to Cartesian coordinates.
SphereFromVector	Converts Cartesian coordinates to spherical coordinates.
EquatorFromVector	Given an equatorial vector, calculates equatorial angular coordinates.
VectorFromHorizon	Given apparent angular horizontal coordinates, calculates horizontal vector.
HorizonFromVector	Given a vector in horizontal orientation, calculates horizontal angular coordinates.
Rotation_EQD_EQJ	Calculates a rotation matrix from equatorial of-date (EQD) to equatorial J2000 (EQJ).
Rotation_EQD_ECL	Calculates a rotation matrix from equatorial of-date (EQD) to ecliptic J2000 (ECL).
Rotation_EQD_HOR	Calculates a rotation matrix from equatorial of-date (EQD) to horizontal (HOR).
Rotation_EQJ_EQD	Calculates a rotation matrix from equatorial J2000 (EQJ) to equatorial of-date (EQD).
Rotation_EQJ_ECL	Calculates a rotation matrix from equatorial J2000 (EQJ) to ecliptic J2000 (ECL).
Rotation_EQJ_HOR	Calculates a rotation matrix from equatorial J2000 (EQJ) to horizontal (HOR).
Rotation_ECL_EQD	Calculates a rotation matrix from ecliptic J2000 (ECL) to equatorial of-date (EQD).
Rotation_ECL_EQJ	Calculates a rotation matrix from ecliptic J2000 (ECL) to equatorial J2000 (EQJ).
Rotation_ECL_HOR	Calculates a rotation matrix from ecliptic J2000 (ECL) to horizontal (HOR).
Rotation_HOR_EQD	Calculates a rotation matrix from horizontal (HOR) to equatorial of-date (EQD).
Rotation_HOR_EQJ	Calculates a rotation matrix from horizontal (HOR) to J2000 equatorial (EQJ).
Rotation_HOR_ECL	Calculates a rotation matrix from horizontal (HOR) to ecliptic J2000 (ECL).
Rotation_EQJ_GAL	Calculates a rotation matrix from equatorial J2000 (EQJ) to galactic (GAL).
Rotation_GAL_EQJ	Calculates a rotation matrix from galactic (GAL) to equatorial J2000 (EQJ).

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