astronomy/source/js

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. Other programming languages are supported also. See the home page for more info.

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Quick Start

To get started quickly, here are some browser scripting examples and some Node.js examples.

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Topic Index

Position of Sun, Moon, and planets

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

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.
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.
SearchMoonQuarter	Find the first quarter moon phase after a given date and time.
NextMoonQuarter	Find 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, find 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, find 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	Find oppositions and conjunctions of planets.

Equinoxes and solstices

Function	Description
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	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.
VectorFromSphere	Converts spherical coordinates to Cartesian coordinates.
SphereFromVector	Converts Cartesian coordinates to spherical coordinates.
VectorFromEquator	Given angular equatorial coordinates, calculates equatorial vector.
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).

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API Reference

Astronomy : object

Kind: global namespace

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Astronomy.AstroTime

Kind: static class of Astronomy
Brief: The date and time of an astronomical observation.

Objects of this type are used throughout the internals of the Astronomy library, and are included in certain return objects. The constructor is not accessible outside the Astronomy library; outside users should call the MakeTime function to create an AstroTime object.
Properties

Name	Type	Description
date	Date	The JavaScript Date object for the given date and time. This Date corresponds to the numeric day value stored in the ut property.
ut	number	Universal Time (UT1/UTC) in fractional days since the J2000 epoch. Universal Time represents time measured with respect to the Earth's rotation, tracking mean solar days. The Astronomy library approximates UT1 and UTC as being the same thing. This gives sufficient accuracy for the precision requirements of this project.
tt	number	Terrestrial Time in fractional days since the J2000 epoch. TT represents a continuously flowing ephemeris timescale independent of any variations of the Earth's rotation, and is adjusted from UT using historical and predictive models of those variations.

• .AstroTime
  • new AstroTime(date)
  • .toString() ⇒ string
  • .AddDays(days) ⇒ AstroTime

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new AstroTime(date)

Param	Type	Description
date	Date | number	A JavaScript Date object or a numeric UTC value expressed in J2000 days.

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astroTime.toString() ⇒ string

Formats an AstroTime object as an ISO 8601 date/time string in UTC, to millisecond resolution. Example: 2018-08-17T17:22:04.050Z

Kind: instance method of AstroTime

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astroTime.AddDays(days) ⇒ AstroTime

Returns a new AstroTime object adjusted by the floating point number of days. Does NOT modify the original AstroTime object.

Kind: instance method of AstroTime

Param	Type	Description
days	number	The floating point number of days by which to adjust the given date and time. Positive values adjust the date toward the future, and negative values adjust the date toward the past.

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Astronomy.Vector

Holds the Cartesian coordinates of a vector in 3D space, along with the time at which the vector is valid.

Kind: static class of Astronomy
Properties

Name	Type	Description
x	number	The x-coordinate expressed in astronomical units (AU).
y	number	The y-coordinate expressed in astronomical units (AU).
z	number	The z-coordinate expressed in astronomical units (AU).
t	AstroTime	The time at which the vector is valid.

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vector.Length() ⇒ number

Returns the length of the vector in astronomical units (AU).

Kind: instance method of Vector

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Astronomy.Spherical

Holds spherical coordinates: latitude, longitude, distance.

Kind: static class of Astronomy
Properties

Name	Type	Description
lat	number	The latitude angle: -90..+90 degrees.
lon	number	The longitude angle: 0..360 degrees.
dist	number	Distance in AU.

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Astronomy.EquatorialCoordinates

Holds right ascension, declination, and distance of a celestial object.

Kind: static class of Astronomy
Properties

Name	Type	Description
ra	number	Right ascension in sidereal hours: [0, 24).
dec	number	Declination in degrees: [-90, +90].
dist	number	Distance to the celestial object expressed in astronomical units (AU).

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Astronomy.RotationMatrix

Contains a rotation matrix that can be used to transform one coordinate system to another.

Kind: static class of Astronomy
Properties

Name	Type	Description
rot	Array.<Array.<number>>	A normalized 3x3 rotation matrix.

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Astronomy.HorizontalCoordinates

Holds azimuth (compass direction) and altitude (angle above/below the horizon) of a celestial object as seen by an observer at a particular location on the Earth's surface. Also holds right ascension and declination of the same object. All of these coordinates are optionally adjusted for atmospheric refraction; therefore the right ascension and declination values may not exactly match those found inside a corresponding EquatorialCoordinates object.

Kind: static class of Astronomy
Properties

Name	Type	Description
azimuth	number	A horizontal compass direction angle in degrees measured starting at north and increasing positively toward the east. The value is in the range [0, 360). North = 0, east = 90, south = 180, west = 270.
altitude	number	A vertical angle in degrees above (positive) or below (negative) the horizon. The value is in the range [-90, +90]. The altitude angle is optionally adjusted upward due to atmospheric refraction.
ra	number	The right ascension of the celestial body in sidereal hours. The value is in the reange [0, 24). If altitude was adjusted for atmospheric reaction, ra is likewise adjusted.
dec	number	The declination of of the celestial body in degrees. The value in the range [-90, +90]. If altitude was adjusted for atmospheric reaction, dec is likewise adjusted.

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Astronomy.EclipticCoordinates

Holds ecliptic coordinates of a celestial body. The origin and date of the coordinate system may vary depending on the caller's usage. In general, ecliptic coordinates are measured with respect to the mean plane of the Earth's orbit around the Sun. Includes Cartesian coordinates (ex, ey, ez) measured in astronomical units (AU) and spherical coordinates (elon, elat) measured in degrees.

Kind: static class of Astronomy
Properties

Name	Type	Description
ex	number	The Cartesian x-coordinate of the body in astronomical units (AU). The x-axis is within the ecliptic plane and is oriented in the direction of the equinox.
ey	number	The Cartesian y-coordinate of the body in astronomical units (AU). The y-axis is within the ecliptic plane and is oriented 90 degrees counterclockwise from the equinox, as seen from above the Sun's north pole.
ez	number	The Cartesian z-coordinate of the body in astronomical units (AU). The z-axis is oriented perpendicular to the ecliptic plane, along the direction of the Sun's north pole.
elat	number	The ecliptic latitude of the body in degrees. This is the angle north or south of the ecliptic plane. The value is in the range [-90, +90]. Positive values are north and negative values are south.
elon	number	The ecliptic longitude of the body in degrees. This is the angle measured counterclockwise around the ecliptic plane, as seen from above the Sun's north pole. This is the same direction that the Earth orbits around the Sun. The angle is measured starting at 0 from the equinox and increases up to 360 degrees.

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Astronomy.Observer

Represents the geographic location of an observer on the surface of the Earth.

Kind: static class of Astronomy
Properties

Name	Type	Description
latitude	number	The observer's geographic latitude in degrees north of the Earth's equator. The value is negative for observers south of the equator. Must be in the range -90 to +90.
longitude	number	The observer's geographic longitude in degrees east of the prime meridian passing through Greenwich, England. The value is negative for observers west of the prime meridian. The value should be kept in the range -180 to +180 to minimize floating point errors.
height	number	The observer's elevation above mean sea level, expressed in meters.

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Astronomy.IlluminationInfo

Contains information about the apparent brightness and sunlit phase of a celestial object.

Kind: static class of Astronomy
Properties

Name	Type	Description
time	AstroTime	The date and time pertaining to the other calculated values in this object.
mag	number	The apparent visual magnitude of the celestial body.
phase_angle	number	The angle in degrees as seen from the center of the celestial body between the Sun and the Earth. The value is always in the range 0 to 180. The phase angle provides a measure of what fraction of the body's face appears illuminated by the Sun as seen from the Earth. When the observed body is the Sun, the phase property is set to 0, although this has no physical meaning because the Sun emits, rather than reflects, light. When the phase is near 0 degrees, the body appears "full". When it is 90 degrees, the body appears "half full". And when it is 180 degrees, the body appears "new" and is very difficult to see because it is both dim and lost in the Sun's glare as seen from the Earth.
phase_fraction	number	The fraction of the body's face that is illuminated by the Sun, as seen from the Earth. Calculated from phase_angle for convenience. This value ranges from 0 to 1.
helio_dist	number	The distance between the center of the Sun and the center of the body in astronomical units (AU).
geo_dist	number	The distance between the center of the Earth and the center of the body in AU.
gc	Vector	Geocentric coordinates: the 3D vector from the center of the Earth to the center of the body. The components are in expressed in AU and are oriented with respect to the J2000 equatorial plane.
hc	Vector	Heliocentric coordinates: The 3D vector from the center of the Sun to the center of the body. Like gc, hc is expressed in AU and oriented with respect to the J2000 equatorial plane.
ring_tilt	number | null	For Saturn, this is the angular tilt of the planet's rings in degrees away from the line of sight from the Earth. When the value is near 0, the rings appear edge-on from the Earth and are therefore difficult to see. When ring_tilt approaches its maximum value (about 27 degrees), the rings appear widest and brightest from the Earth. Unlike the JPL Horizons online tool, this library includes the effect of the ring tilt angle in the calculated value for Saturn's visual magnitude. For all bodies other than Saturn, the value of ring_tilt is null.

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Astronomy.MoonQuarter

Represents a quarter lunar phase, along with when it occurs.

Kind: static class of Astronomy
Properties

Name	Type	Description
quarter	number	An integer as follows: 0 = new moon, 1 = first quarter, 2 = full moon, 3 = third quarter.
time	AstroTime	The date and time of the quarter lunar phase.

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Astronomy.HourAngleEvent

Returns information about an occurrence of a celestial body reaching a given hour angle as seen by an observer at a given location on the surface of the Earth.

Kind: static class of Astronomy
Properties

Name	Type	Description
time	AstroTime	The date and time of the celestial body reaching the hour angle.
hor	HorizontalCoordinates	Topocentric horizontal coordinates for the body at the time indicated by the time property.

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Astronomy.SeasonInfo

Represents the dates and times of the two solstices and the two equinoxes in a given calendar year. These four events define the changing of the seasons on the Earth.

Kind: static class of Astronomy
Properties

Name	Type	Description
mar_equinox	AstroTime	The date and time of the March equinox in the given calendar year. This is the moment in March that the plane of the Earth's equator passes through the center of the Sun; thus the Sun's declination changes from a negative number to a positive number. The March equinox defines the beginning of spring in the northern hemisphere and the beginning of autumn in the southern hemisphere.
jun_solstice	AstroTime	The date and time of the June solstice in the given calendar year. This is the moment in June that the Sun reaches its most positive declination value. At this moment the Earth's north pole is most tilted most toward the Sun. The June solstice defines the beginning of summer in the northern hemisphere and the beginning of winter in the southern hemisphere.
sep_equinox	AstroTime	The date and time of the September equinox in the given calendar year. This is the moment in September that the plane of the Earth's equator passes through the center of the Sun; thus the Sun's declination changes from a positive number to a negative number. The September equinox defines the beginning of autumn in the northern hemisphere and the beginning of spring in the southern hemisphere.
dec_solstice	AstroTime	The date and time of the December solstice in the given calendar year. This is the moment in December that the Sun reaches its most negative declination value. At this moment the Earth's south pole is tilted most toward the Sun. The December solstice defines the beginning of winter in the northern hemisphere and the beginning of summer in the southern hemisphere.

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Astronomy.ElongationEvent

Represents the angular separation of a body from the Sun as seen from the Earth and the relative ecliptic longitudes between that body and the Earth as seen from the Sun.

Kind: static class of Astronomy
See: Elongation
Properties

Name	Type	Description
time	AstroTime	The date and time of the observation.
visibility	string	Either "morning" or "evening", indicating when the body is most easily seen.
elongation	number	The angle in degrees, as seen from the center of the Earth, of the apparent separation between the body and the Sun. This angle is measured in 3D space and is not projected onto the ecliptic plane. When elongation is less than a few degrees, the body is very difficult to see from the Earth because it is lost in the Sun's glare. The elongation is always in the range [0, 180].
ecliptic_separation	number	The absolute value of the difference between the body's ecliptic longitude and the Sun's ecliptic longitude, both as seen from the center of the Earth. This angle measures around the plane of the Earth's orbit (the ecliptic), and ignores how far above or below that plane the body is. The ecliptic separation is measured in degrees and is always in the range [0, 180].

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Astronomy.Apsis

Represents a closest or farthest point in a body's orbit around its primary. For a planet orbiting the Sun, this is a perihelion or aphelion, respectively. For the Moon orbiting the Earth, this is a perigee or apogee, respectively.

Kind: static class of Astronomy
See

• SearchLunarApsis
• NextLunarApsis

Properties

Name	Type	Description
time	AstroTime	The date and time of the apsis.
kind	number	For a closest approach (perigee or perihelion), kind is 0. For a farthest distance event (apogee or aphelion), kind is 1.
dist_au	number	The distance between the centers of the two bodies in astronomical units (AU).
dist_km	number	The distance between the centers of the two bodies in kilometers.

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Astronomy.ConstellationInfo

Reports the constellation that a given celestial point lies within.

Kind: static class of Astronomy
Properties

Name	Type	Description
symbol	string	3-character mnemonic symbol for the constellation, e.g. "Ori".
name	string	Full name of constellation, e.g. "Orion".
ra1875	number	Right ascension expressed in B1875 coordinates.
dec1875	number	Declination expressed in B1875 coordinates.

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Astronomy.LunarEclipseInfo

Returns information about a lunar eclipse.

Returned by SearchLunarEclipse or NextLunarEclipse to report information about a lunar eclipse event. When a lunar eclipse is found, it is classified as penumbral, partial, or total. Penumbral eclipses are difficult to observe, because the moon is only slightly dimmed by the Earth's penumbra; no part of the Moon touches the Earth's umbra. Partial eclipses occur when part, but not all, of the Moon touches the Earth's umbra. Total eclipses occur when the entire Moon passes into the Earth's umbra.

The kind field thus holds one of the strings "penumbral", "partial", or "total", depending on the kind of lunar eclipse found.

Field peak holds the date and time of the peak of the eclipse, when it is at its peak.

Fields sd_penum, sd_partial, and sd_total hold the semi-duration of each phase of the eclipse, which is half of the amount of time the eclipse spends in each phase (expressed in minutes), or 0 if the eclipse never reaches that phase. By converting from minutes to days, and subtracting/adding with peak, the caller may determine the date and time of the beginning/end of each eclipse phase.

Kind: static class of Astronomy
Properties

Name	Type	Description
kind	string	The type of lunar eclipse found.
peak	AstroTime	The time of the eclipse at its peak.
sd_penum	number	The semi-duration of the penumbral phase in minutes.
sd_partial	number	The semi-duration of the penumbral phase in minutes, or 0.0 if none.
sd_total	number	The semi-duration of the penumbral phase in minutes, or 0.0 if none.

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Astronomy.GlobalSolarEclipseInfo

Reports the time and geographic location of the peak of a solar eclipse.

Returned by [SearchGlobalSolarEclipse](#Astronomy.SearchGlobalSolarEclipse) or [NextGlobalSolarEclipse](#Astronomy.NextGlobalSolarEclipse)
to report information about a solar eclipse event.

Field `peak` holds the date and time of the peak of the eclipse, defined as
the instant when the axis of the Moon's shadow cone passes closest to the Earth's center.

The eclipse is classified as partial, annular, or total, depending on the
maximum amount of the Sun's disc obscured, as seen at the peak location
on the surface of the Earth.

The `kind` field thus holds one of the strings `"partial"`, `"annular"`, or `"total"`.
A total eclipse is when the peak observer sees the Sun completely blocked by the Moon.
An annular eclipse is like a total eclipse, but the Moon is too far from the Earth's surface
to completely block the Sun; instead, the Sun takes on a ring-shaped appearance.
A partial eclipse is when the Moon blocks part of the Sun's disc, but nobody on the Earth
observes either a total or annular eclipse.

If `kind` is `"total"` or `"annular"`, the `latitude` and `longitude`
fields give the geographic coordinates of the center of the Moon's shadow projected
onto the daytime side of the Earth at the instant of the eclipse's peak.
If `kind` has any other value, `latitude` and `longitude` are undefined and should
not be used.

Kind: static class of Astronomy
Properties

Name	Type	Description
kind	string	One of the following string values: "partial", "annular", "total".
peak	AstroTime	The date and time of the peak of the eclipse, defined as the instant when the axis of the Moon's shadow cone passes closest to the Earth's center.
distance	number	The distance in kilometers between the axis of the Moon's shadow cone and the center of the Earth at the time indicated by peak.
latitude	undefined | number	If kind holds "total", the geographic latitude in degrees where the center of the Moon's shadow falls on the Earth at the time indicated by peak; otherwise, latitude holds undefined.
longitude	undefined | number	If kind holds "total", the geographic longitude in degrees where the center of the Moon's shadow falls on the Earth at the time indicated by peak; otherwise, longitude holds undefined.

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Astronomy.EclipseEvent

Kind: static class of Astronomy
Brief: Holds a time and the observed altitude of the Sun at that time.

When reporting a solar eclipse observed at a specific location on the Earth (a "local" solar eclipse), a series of events occur. In addition to the time of each event, it is important to know the altitude of the Sun, because each event may be invisible to the observer if the Sun is below the horizon (i.e. it at night).

If altitude is negative, the event is theoretical only; it would be visible if the Earth were transparent, but the observer cannot actually see it. If altitude is positive but less than a few degrees, visibility will be impaired by atmospheric interference (sunrise or sunset conditions).
Properties

Name	Type	Description
time	AstroTime	The date and time of the event.
altitude	number	The angular altitude of the center of the Sun above/below the horizon, at time, corrected for atmospheric refraction and expressed in degrees.

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Astronomy.LocalSolarEclipseInfo

Kind: static class of Astronomy
Brief: Information about a solar eclipse as seen by an observer at a given time and geographic location.

Returned by SearchLocalSolarEclipse or NextLocalSolarEclipse to report information about a solar eclipse as seen at a given geographic location.

When a solar eclipse is found, it is classified by setting kind to "partial", "annular", or "total". A partial solar eclipse is when the Moon does not line up directly enough with the Sun to completely block the Sun's light from reaching the observer. An annular eclipse occurs when the Moon's disc is completely visible against the Sun but the Moon is too far away to completely block the Sun's light; this leaves the Sun with a ring-like appearance. A total eclipse occurs when the Moon is close enough to the Earth and aligned with the Sun just right to completely block all sunlight from reaching the observer.

There are 5 "event" fields, each of which contains a time and a solar altitude. Field peak holds the date and time of the center of the eclipse, when it is at its peak. The fields partial_begin and partial_end are always set, and indicate when the eclipse begins/ends. If the eclipse reaches totality or becomes annular, total_begin and total_end indicate when the total/annular phase begins/ends. When an event field is valid, the caller must also check its altitude field to see whether the Sun is above the horizon at the time indicated by the time field. See #EclipseEvent for more information.
Properties

Name	Type	Description
kind	string	The type of solar eclipse found: "partial", "annular", or "total".
partial_begin	EclipseEvent	The time and Sun altitude at the beginning of the eclipse.
total_begin	EclipseEvent	If this is an annular or a total eclipse, the time and Sun altitude when annular/total phase begins; otherwise undefined.
peak	EclipseEvent	The time and Sun altitude when the eclipse reaches its peak.
total_end	EclipseEvent	If this is an annular or a total eclipse, the time and Sun altitude when annular/total phase ends; otherwise undefined.
partial_end	EclipseEvent	The time and Sun altitude at the end of the eclipse.

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Astronomy.TransitInfo

Kind: static class of Astronomy
Brief: Information about a transit of Mercury or Venus, as seen from the Earth.

Returned by SearchTransit or NextTransit to report information about a transit of Mercury or Venus. A transit is when Mercury or Venus passes between the Sun and Earth so that the other planet is seen in silhouette against the Sun.

The calculations are performed from the point of view of a geocentric observer.
Properties

Name	Type	Description
start	AstroTime	The date and time at the beginning of the transit. This is the moment the planet first becomes visible against the Sun in its background.
peak	AstroTime	When the planet is most aligned with the Sun, as seen from the Earth.
finish	AstroTime	The date and time at the end of the transit. This is the moment the planet is last seen against the Sun in its background.
separation;	number	The minimum angular separation, in arcminutes, between the centers of the Sun and the planet. This angle pertains to the time stored in peak.

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Astronomy.Bodies : Array.<string>

An array of strings, each a name of a supported astronomical body. Not all bodies are valid for all functions, but any string not in this list is not supported at all.

Kind: static constant of Astronomy

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Astronomy.MakeTime(date) ⇒ AstroTime

Given a Date object or a number days since noon (12:00) on January 1, 2000 (UTC), this function creates an AstroTime object. Given an AstroTime object, returns the same object unmodified. Use of this function is not required for any of the other exposed functions in this library, because they all guarantee converting date/time parameters to Astronomy.AstroTime as needed. However, it may be convenient for callers who need to understand the difference between UTC and TT (Terrestrial Time). In some use cases, converting once to Astronomy.AstroTime format and passing the result into multiple function calls may be more efficient than passing in native JavaScript Date objects.

Kind: static method of Astronomy

Param	Type	Description
date	Date | number | AstroTime	A Date object, a number of UTC days since the J2000 epoch (noon on January 1, 2000), or an Astronomy.AstroTime object. See remarks above.

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Astronomy.MakeSpherical(lat, lon, dist) ⇒ Spherical

Create spherical coordinates.

Kind: static method of Astronomy

Param	Type	Description
lat	number	The angular distance above or below the reference plane, in degrees.
lon	number	The angular distance around the reference plane, in degrees.
dist	number	A radial distance in AU.

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Astronomy.MakeRotation(rot) ⇒ RotationMatrix

Creates a rotation matrix that can be used to transform one coordinate system to another.

Kind: static method of Astronomy

Param	Type	Description
rot	Array.<Array.<number>>	An array [3][3] of numbers. Defines a rotation matrix used to premultiply a 3D vector to reorient it into another coordinate system.

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Astronomy.Horizon(date, observer, ra, dec, refraction) ⇒ HorizontalCoordinates

Given a date and time, a geographic location of an observer on the Earth, and equatorial coordinates (right ascension and declination) of a celestial body, returns horizontal coordinates (azimuth and altitude angles) for that body as seen by that observer. Allows optional correction for atmospheric refraction.

Kind: static method of Astronomy

Param	Type	Description
date	Date | number | AstroTime	The date and time for which to find horizontal coordinates.
observer	Observer	The location of the observer for which to find horizontal coordinates.
ra	number	Right ascension in sidereal hours of the celestial object, referred to the mean equinox of date for the J2000 epoch.
dec	number	Declination in degrees of the celestial object, referred to the mean equator of date for the J2000 epoch. Positive values are north of the celestial equator and negative values are south.
refraction	string	If omitted or has a false-like value (false, null, undefined, etc.) the calculations are performed without any correction for atmospheric refraction. If the value is the string "normal", uses the recommended refraction correction based on Meeus "Astronomical Algorithms" with a linear taper more than 1 degree below the horizon. The linear taper causes the refraction to linearly approach 0 as the altitude of the body approaches the nadir (-90 degrees). If the value is the string "jplhor", uses a JPL Horizons compatible formula. This is the same algorithm as "normal", only without linear tapering; this can result in physically impossible altitudes of less than -90 degrees, which may cause problems for some applications. (The "jplhor" option was created for unit testing against data generated by JPL Horizons, and is otherwise not recommended for use.)

---

Astronomy.MakeObserver(latitude_degrees, longitude_degrees, height_in_meters)

Creates an Observer object that represents a location on the surface of the Earth from which observations are made.

Kind: static method of Astronomy

Param	Type	Description
latitude_degrees	number	The observer's geographic latitude in degrees north of the Earth's equator. The value is negative for observers south of the equator. Must be in the range -90 to +90.
longitude_degrees	number	The observer's geographic longitude in degrees east of the prime meridian passing through Greenwich, England. The value is negative for observers west of the prime meridian. The value should be kept in the range -180 to +180 to minimize floating point errors.
height_in_meters	number	The observer's elevation above mean sea level, expressed in meters. If omitted, the elevation is assumed to be 0 meters.

---

Astronomy.SunPosition(date) ⇒ EclipticCoordinates

Returns apparent geocentric true ecliptic coordinates of date for the Sun. Geocentric means coordinates as the Sun would appear to a hypothetical observer at the center of the Earth. Ecliptic coordinates of date are measured along the plane of the Earth's mean orbit around the Sun, using the equinox of the Earth as adjusted for precession and nutation of the Earth's axis of rotation on the given date.

Kind: static method of Astronomy

Param	Type	Description
date	Date | number | AstroTime	The date and time at which to calculate the Sun's apparent location as seen from the center of the Earth.

---

Astronomy.Equator(body, date, observer, ofdate, aberration) ⇒ EquatorialCoordinates

Returns topocentric equatorial coordinates (right ascension and declination) in one of two different systems: J2000 or true-equator-of-date. Allows optional correction for aberration. Always corrects for light travel time (represents the object as seen by the observer with light traveling to the Earth at finite speed, not where the object is right now). Topocentric refers to a position as seen by an observer on the surface of the Earth. This function corrects for parallax of the object between a geocentric observer and a topocentric observer. This is most significant for the Moon, because it is so close to the Earth. However, it can have a small effect on the apparent positions of other bodies.

Kind: static method of Astronomy
Returns: EquatorialCoordinates - The topocentric coordinates of the body as adjusted for the given observer.

Param	Type	Description
body	string	The name of the body for which to find equatorial coordinates. Not allowed to be "Earth".
date	Date | number | Astronomy.Time	Specifies the date and time at which the body is to be observed.
observer	Observer	The location on the Earth of the observer. Call MakeObserver to create an observer object.
ofdate	bool	Pass true to return equatorial coordinates of date, i.e. corrected for precession and nutation at the given date. This is needed to get correct horizontal coordinates when you call Horizon. Pass false to return equatorial coordinates in the J2000 system.
aberration	bool	Pass true to correct for aberration, or false to leave uncorrected.

---

Astronomy.Ecliptic(gx, gy, gz) ⇒ EclipticCoordinates

Given J2000 equatorial Cartesian coordinates, returns J2000 ecliptic latitude, longitude, and cartesian coordinates. You can call GeoVector and use its (x, y, z) return values to pass into this function.

Kind: static method of Astronomy

Param	Type	Description
gx	number	The x-coordinate of a 3D vector in the J2000 equatorial coordinate system.
gy	number	The y-coordinate of a 3D vector in the J2000 equatorial coordinate system.
gz	number	The z-coordinate of a 3D vector in the J2000 equatorial coordinate system.

---

Astronomy.GeoMoon(date) ⇒ Vector

Calculates the geocentric Cartesian coordinates for the Moon in the J2000 equatorial system. Based on the Nautical Almanac Office's Improved Lunar Ephemeris of 1954, which in turn derives from E. W. Brown's lunar theories. Adapted from Turbo Pascal code from the book Astronomy on the Personal Computer by Montenbruck and Pfleger.

Kind: static method of Astronomy

Param	Type	Description
date	Date | number | AstroTime	The date and time for which to calculate the Moon's geocentric position.

---

Astronomy.HelioVector(body, date) ⇒ Vector

Calculates heliocentric (i.e., with respect to the center of the Sun) Cartesian coordinates in the J2000 equatorial system of a celestial body at a specified time. The position is not corrected for light travel time or aberration.

Kind: static method of Astronomy

Param	Type	Description
body	string	One of the strings "Sun", "Moon", "Mercury", "Venus", "Earth", "Mars", "Jupiter", "Saturn", "Uranus", "Neptune", "Pluto", "SSB", or "EMB".
date	Date | number | AstroTime	The date and time for which the body's position is to be calculated.

---

Astronomy.HelioDistance(body, date) ⇒ number

Calculates the distance between a body and the Sun at a given time.

Given a date and time, this function calculates the distance between the center of body and the center of the Sun. For the planets Mercury through Neptune, this function is significantly more efficient than calling HelioVector followed by taking the length of the resulting vector.

Kind: static method of Astronomy
Returns: number - The heliocentric distance in AU.

Param	Type	Description
body	string	A body for which to calculate a heliocentric distance: the Sun, Moon, or any of the planets.
date	Date | number | AstroTime	The date and time for which to calculate the heliocentric distance.

---

Astronomy.GeoVector(body, date, aberration) ⇒ Vector

Calculates geocentric (i.e., with respect to the center of the Earth) Cartesian coordinates in the J2000 equatorial system of a celestial body at a specified time. The position is always corrected for light travel time: this means the position of the body is "back-dated" based on how long it takes light to travel from the body to an observer on the Earth. Also, the position can optionally be corrected for aberration, an effect causing the apparent direction of the body to be shifted based on transverse movement of the Earth with respect to the rays of light coming from that body.

Kind: static method of Astronomy

Param	Type	Description
body	string	One of the strings "Sun", "Moon", "Mercury", "Venus", "Earth", "Mars", "Jupiter", "Saturn", "Uranus", "Neptune", or "Pluto".
date	Date | number | AstroTime	The date and time for which the body's position is to be calculated.
aberration	bool	Pass true to correct for aberration, or false to leave uncorrected.

---

Astronomy.Search(func, t1, t2, options) ⇒ null | AstroTime

Search for next time t (such that t is between t1 and t2) that func(t) crosses from a negative value to a non-negative value. The given function must have "smooth" behavior over the entire inclusive range [t1, t2], meaning that it behaves like a continuous differentiable function. It is not required that t1 < t2; t1 > t2 allows searching backward in time. Note: t1 and t2 must be chosen such that there is no possibility of more than one zero-crossing (ascending or descending), or it is possible that the "wrong" event will be found (i.e. not the first event after t1) or even that the function will return null, indicating that no event was found.

Kind: static method of Astronomy
Returns: null | AstroTime - If the search is successful, returns the date and time of the solution. If the search fails, returns null.

Param	Type	Description
func	ContinuousFunction	The function to find an ascending zero crossing for. The function must accept a single parameter of type AstroTime and return a numeric value.
t1	AstroTime	The lower time bound of a search window.
t2	AstroTime	The upper time bound of a search window.
options	null | SearchOptions	Options that can tune the behavior of the search. Most callers can omit this argument or pass in null.

---

Astronomy.SearchSunLongitude(targetLon, dateStart, limitDays) ⇒ AstroTime | null

Searches for the moment in time when the center of the Sun reaches a given apparent ecliptic longitude, as seen from the center of the Earth, within a given range of dates. This function can be used to determine equinoxes and solstices. However, it is usually more convenient and efficient to call Seasons to calculate equinoxes and solstices for a given calendar year. SearchSunLongitude is more general in that it allows searching for arbitrary longitude values.

Kind: static method of Astronomy
Returns: AstroTime | null - The date and time when the Sun reaches the apparent ecliptic longitude targetLon within the range of times specified by dateStart and limitDays. If the Sun does not reach the target longitude within the specified time range, or the time range is excessively wide, the return value is null. To avoid a null return value, the caller must pick a time window around the event that is within a few days but not so small that the event might fall outside the window.

Param	Type	Description
targetLon	number	The desired ecliptic longitude of date in degrees. This may be any value in the range [0, 360), although certain values have conventional meanings: When targetLon is 0, finds the March equinox, which is the moment spring begins in the northern hemisphere and the beginning of autumn in the southern hemisphere. When targetLon is 180, finds the September equinox, which is the moment autumn begins in the northern hemisphere and spring begins in the southern hemisphere. When targetLon is 90, finds the northern solstice, which is the moment summer begins in the northern hemisphere and winter begins in the southern hemisphere. When targetLon is 270, finds the southern solstice, which is the moment winter begins in the northern hemisphere and summer begins in the southern hemisphere.
dateStart	Date | number | AstroTime	A date and time known to be earlier than the desired longitude event.
limitDays	number	A floating point number of days, which when added to dateStart, yields a date and time known to be after the desired longitude event.

---

Astronomy.LongitudeFromSun(body, date) ⇒ number

Calculates the ecliptic longitude difference between the given body and the Sun as seen from the Earth at a given moment in time. The returned value ranges [0, 360) degrees. By definition, the Earth and the Sun are both in the plane of the ecliptic. Ignores the height of the body above or below the ecliptic plane; the resulting angle is measured around the ecliptic plane for the "shadow" of the body onto that plane.

Kind: static method of Astronomy
Returns: number - An angle in degrees in the range [0, 360). Values less than 180 indicate that the body is to the east of the Sun as seen from the Earth; that is, the body sets after the Sun does and is visible in the evening sky. Values greater than 180 indicate that the body is to the west of the Sun and is visible in the morning sky.

Param	Type	Description
body	string	The name of a supported celestial body other than the Earth.
date	Date | number | AstroTime	The time at which the relative longitude is to be found.

---

Astronomy.AngleFromSun(body, date) ⇒ number

Returns the full angle seen from the Earth, between the given body and the Sun. Unlike LongitudeFromSun, this function does not project the body's "shadow" onto the ecliptic; the angle is measured in 3D space around the plane that contains the centers of the Earth, the Sun, and body.

Kind: static method of Astronomy
Returns: number - An angle in degrees in the range [0, 180].

Param	Type	Description
body	string	The name of a supported celestial body other than the Earth.
date	Date | number | AstroTime	The time at which the angle from the Sun is to be found.

---

Astronomy.EclipticLongitude(body, date) ⇒ number

Calculates heliocentric ecliptic longitude based on the J2000 equinox.

Kind: static method of Astronomy
Returns: number - The ecliptic longitude angle of the body in degrees measured counterclockwise around the mean plane of the Earth's orbit, as seen from above the Sun's north pole. Ecliptic longitude starts at 0 at the J2000 equinox and increases in the same direction the Earth orbits the Sun. The returned value is always in the range [0, 360).

Param	Type	Description
body	string	The name of a celestial body other than the Sun.
date	Date | number | AstroTime	The date and time for which to calculate the ecliptic longitude.

---

Astronomy.Illumination(body, date) ⇒ IlluminationInfo

Calculates the phase angle, visual maginitude, and other values relating to the body's illumination at the given date and time, as seen from the Earth.

Kind: static method of Astronomy

Param	Type	Description
body	string	The name of the celestial body being observed. Not allowed to be "Earth".
date	Date | number | AstroTime	The date and time for which to calculate the illumination data for the given body.

---

Astronomy.SearchRelativeLongitude(body, targetRelLon, startDate) ⇒ AstroTime

Searches for the date and time the relative ecliptic longitudes of the specified body and the Earth, as seen from the Sun, reach a certain difference. This function is useful for finding conjunctions and oppositions of the planets. For the opposition of a superior planet (Mars, Jupiter, ..., Pluto), or the inferior conjunction of an inferior planet (Mercury, Venus), call with targetRelLon = 0. The 0 value indicates that both planets are on the same ecliptic longitude line, ignoring the other planet's distance above or below the plane of the Earth's orbit. For superior conjunctions, call with targetRelLon = 180. This means the Earth and the other planet are on opposite sides of the Sun.

Kind: static method of Astronomy
Returns: AstroTime - The time when the Earth and the body next reach the specified relative longitudes.

Param	Type	Description
body	string	The name of a planet other than the Earth.
targetRelLon	number	The desired angular difference in degrees between the ecliptic longitudes of body and the Earth. Must be in the range (-180, +180].
startDate	Date | number | AstroTime	The date and time after which to find the next occurrence of the body and the Earth reaching the desired relative longitude.

---

Astronomy.MoonPhase(date) ⇒ number

Determines the moon's phase expressed as an ecliptic longitude.

Kind: static method of Astronomy
Returns: number - A value in the range [0, 360) indicating the difference in ecliptic longitude between the center of the Sun and the center of the Moon, as seen from the center of the Earth. Certain longitude values have conventional meanings:

• 0 = new moon
• 90 = first quarter
• 180 = full moon
• 270 = third quarter

Param	Type	Description
date	Date | number | AstroTime	The date and time for which to calculate the moon's phase.

---

Astronomy.SearchMoonPhase(targetLon, dateStart, limitDays) ⇒ AstroTime | null

Searches for the date and time that the Moon reaches a specified phase. Lunar phases are defined in terms of geocentric ecliptic longitudes with respect to the Sun. When the Moon and the Sun have the same ecliptic longitude, that is defined as a new moon. When the two ecliptic longitudes are 180 degrees apart, that is defined as a full moon. To enumerate quarter lunar phases, it is simpler to call SearchMoonQuarter once, followed by repeatedly calling NextMoonQuarter. SearchMoonPhase is only necessary for finding other lunar phases than the usual quarter phases.

Kind: static method of Astronomy
Returns: AstroTime | null - If the specified lunar phase occurs after dateStart and before limitDays days after dateStart, this function returns the date and time of the first such occurrence. Otherwise, it returns null.

Param	Type	Description
targetLon	number	The difference in geocentric ecliptic longitude between the Sun and Moon that specifies the lunar phase being sought. This can be any value in the range [0, 360). Here are some helpful examples: 0 = new moon, 90 = first quarter, 180 = full moon, 270 = third quarter.
dateStart	Date | number | AstroTime	The beginning of the window of time in which to search.
limitDays	number	The floating point number of days after dateStart that limits the window of time in which to search.

---

Astronomy.SearchMoonQuarter(dateStart) ⇒ MoonQuarter

Finds the first quarter lunar phase after the specified date and time. The quarter lunar phases are: new moon, first quarter, full moon, and third quarter. To enumerate quarter lunar phases, call SearchMoonQuarter once, then pass its return value to NextMoonQuarter to find the next MoonQuarter. Keep calling NextMoonQuarter in a loop, passing the previous return value as the argument to the next call.

Kind: static method of Astronomy

Param	Type	Description
dateStart	Date | number | AstroTime	The date and time after which to find the first quarter lunar phase.

---

Astronomy.NextMoonQuarter(mq)

Given a MoonQuarter object, finds the next consecutive quarter lunar phase. See remarks in SearchMoonQuarter for explanation of usage.

Kind: static method of Astronomy

Param	Type	Description
mq	MoonQuarter	The return value of a prior call to MoonQuarter or NextMoonQuarter.

---

Astronomy.SearchRiseSet(body, observer, direction, dateStart, limitDays) ⇒ AstroTime | null

Finds a rise or set time for the given body as seen by an observer at the specified location on the Earth. Rise time is defined as the moment when the top of the body is observed to first appear above the horizon in the east. Set time is defined as the moment the top of the body is observed to sink below the horizon in the west. The times are adjusted for typical atmospheric refraction conditions.

Kind: static method of Astronomy
Returns: AstroTime | null - The date and time of the rise or set event, or null if no such event occurs within the specified time window.

Param	Type	Description
body	string	The name of the body to find the rise or set time for.
observer	Observer	Specifies the geographic coordinates and elevation above sea level of the observer. Call MakeObserver to create an observer object.
direction	number	Either +1 to find rise time or -1 to find set time. Any other value will cause an exception to be thrown.
dateStart	Date | number | AstroTime	The date and time after which the specified rise or set time is to be found.
limitDays	number	The fractional number of days after dateStart that limits when the rise or set time is to be found.

---

Astronomy.SearchHourAngle(body, observer, hourAngle, dateStart) ⇒ HourAngleEvent

Finds the next time the given body is seen to reach the specified hour angle by the given observer. Providing hourAngle = 0 finds the next maximum altitude event (culmination). Providing hourAngle = 12 finds the next minimum altitude event. Note that, especially close to the Earth's poles, a body as seen on a given day may always be above the horizon or always below the horizon, so the caller cannot assume that a culminating object is visible nor that an object is below the horizon at its minimum altitude.

Kind: static method of Astronomy

Param	Type	Description
body	string	The name of a celestial body other than the Earth.
observer	Observer	Specifies the geographic coordinates and elevation above sea level of the observer. Call MakeObserver to create an observer object.
hourAngle	number	The hour angle expressed in sidereal hours for which the caller seeks to find the body attain. The value must be in the range [0, 24). The hour angle represents the number of sidereal hours that have elapsed since the most recent time the body crossed the observer's local meridian. This specifying hourAngle = 0 finds the moment in time the body reaches the highest angular altitude in a given sidereal day.
dateStart	Date | number | AstroTime	The date and time after which the desired hour angle crossing event is to be found.

---

Astronomy.Seasons(year) ⇒ SeasonInfo

Finds the equinoxes and solstices for a given calendar year.

Kind: static method of Astronomy

Param	Type	Description
year	number | AstroTime	The integer value or AstroTime object that specifies the UTC calendar year for which to find equinoxes and solstices.

---

Astronomy.Elongation(body) ⇒ ElongationEvent

Calculates angular separation of a body from the Sun as seen from the Earth and the relative ecliptic longitudes between that body and the Earth as seen from the Sun. See the return type ElongationEvent for details.

This function is helpful for determining how easy it is to view a planet away from the Sun's glare on a given date. It also determines whether the object is visible in the morning or evening; this is more important the smaller the elongation is. It is also used to determine how far a planet is from opposition, conjunction, or quadrature.

Kind: static method of Astronomy

Param	Type	Description
body	string	The name of the observed body. Not allowed to be "Earth".

---

Astronomy.SearchMaxElongation(body, startDate) ⇒ ElongationEvent

Searches for the next maximum elongation event for Mercury or Venus that occurs after the given start date. Calling with other values of body will result in an exception. Maximum elongation occurs when the body has the greatest angular separation from the Sun, as seen from the Earth. Returns an ElongationEvent object containing the date and time of the next maximum elongation, the elongation in degrees, and whether the body is visible in the morning or evening.

Kind: static method of Astronomy

Param	Type	Description
body	string	Either "Mercury" or "Venus".
startDate	Date	The date and time after which to search for the next maximum elongation event.

---

Astronomy.SearchPeakMagnitude(body, startDate) ⇒ IlluminationInfo

Searches for the date and time Venus will next appear brightest as seen from the Earth.

Kind: static method of Astronomy

Param	Type	Description
body	string	Currently only "Venus" is supported. Mercury's peak magnitude occurs at superior conjunction, when it is virtually impossible to see from Earth, so peak magnitude events have little practical value for that planet. The Moon reaches peak magnitude very close to full moon, which can be found using SearchMoonQuarter or SearchMoonPhase. The other planets reach peak magnitude very close to opposition, which can be found using SearchRelativeLongitude.
startDate	Date | number | AstroTime	The date and time after which to find the next peak magnitude event.

---

Astronomy.SearchLunarApsis(startDate) ⇒ Apsis

Finds the next perigee (closest approach) or apogee (farthest remove) of the Moon that occurs after the specified date and time.

Kind: static method of Astronomy

Param	Type	Description
startDate	Date | number | AstroTime	The date and time after which to find the next perigee or apogee.

---

Astronomy.NextLunarApsis(apsis) ⇒ Apsis

Given a lunar apsis returned by an initial call to SearchLunarApsis, or a previous call to NextLunarApsis, finds the next lunar apsis. If the given apsis is a perigee, this function finds the next apogee, and vice versa.

Kind: static method of Astronomy
Returns: Apsis - The successor apogee for the given perigee, or the successor perigee for the given apogee.

Param	Type	Description
apsis	Apsis	A lunar perigee or apogee event.

---

Astronomy.SearchPlanetApsis(body, startTime) ⇒ Apsis

Finds the date and time of a planet's perihelion (closest approach to the Sun) or aphelion (farthest distance from the Sun) after a given time.

Given a date and time to start the search in startTime, this function finds the next date and time that the center of the specified planet reaches the closest or farthest point in its orbit with respect to the center of the Sun, whichever comes first after startTime.

The closest point is called perihelion and the farthest point is called aphelion. The word apsis refers to either event.

To iterate through consecutive alternating perihelion and aphelion events, call SearchPlanetApsis once, then use the return value to call NextPlanetApsis. After that, keep feeding the previous return value from NextPlanetApsis into another call of NextPlanetApsis as many times as desired.

Kind: static method of Astronomy
Returns: Apsis - The next perihelion or aphelion that occurs after startTime.

Param	Type	Description
body	string	The planet for which to find the next perihelion/aphelion event. Not allowed to be "Sun" or "Moon".
startTime	AstroTime	The date and time at which to start searching for the next perihelion or aphelion.

---

Astronomy.NextPlanetApsis(body, apsis) ⇒ Apsis

Finds the next planetary perihelion or aphelion event in a series.

This function requires an Apsis value obtained from a call to SearchPlanetApsis or NextPlanetApsis. Given an aphelion event, this function finds the next perihelion event, and vice versa. See SearchPlanetApsis for more details.

Kind: static method of Astronomy
Returns: Apsis - Same as the return value for SearchPlanetApsis.

Param	Type	Description
body	string	The planet for which to find the next perihelion/aphelion event. Not allowed to be "Sun" or "Moon". Must match the body passed into the call that produced the apsis parameter.
apsis	Apsis	An apsis event obtained from a call to SearchPlanetApsis or NextPlanetApsis.

---

Astronomy.InverseRotation(rotation) ⇒ RotationMatrix

Calculates the inverse of a rotation matrix. Given a rotation matrix that performs some coordinate transform, this function returns the matrix that reverses that trasnform.

Kind: static method of Astronomy
Returns: RotationMatrix - The inverse rotation matrix.

Param	Type	Description
rotation	RotationMatrix	The rotation matrix to be inverted.

---

Astronomy.CombineRotation(a, b) ⇒ RotationMatrix

Creates a rotation based on applying one rotation followed by another. Given two rotation matrices, returns a combined rotation matrix that is equivalent to rotating based on the first matrix, followed by the second.

Kind: static method of Astronomy
Returns: RotationMatrix - The combined rotation matrix.

Param	Type	Description
a	RotationMatrix	The first rotation to apply.
b	RotationMatrix	The second rotation to apply.

---

Astronomy.VectorFromSphere(sphere, time) ⇒ Vector

Converts spherical coordinates to Cartesian coordinates. Given spherical coordinates and a time at which they are valid, returns a vector of Cartesian coordinates. The returned value includes the time, as required by AstroTime.

Kind: static method of Astronomy
Returns: Vector - The vector form of the supplied spherical coordinates.

Param	Type	Description
sphere	Spherical	Spherical coordinates to be converted.
time	AstroTime	The time that should be included in the returned vector.

---

Astronomy.VectorFromEquator(equ, time) ⇒ Vector

Given angular equatorial coordinates in equ, calculates equatorial vector.

Kind: static method of Astronomy
Returns: Vector - A vector in the equatorial system.

Param	Type	Description
equ	EquatorialCoordinates	An object that contains angular equatorial coordinates to be converted to a vector.
time	AstroTime	The date and time of the observation. This is needed because the returned vector object requires a valid time value when passed to certain other functions.

---

Astronomy.EquatorFromVector(vec) ⇒ EquatorialCoordinates

Given an equatorial vector, calculates equatorial angular coordinates.

Kind: static method of Astronomy
Returns: EquatorialCoordinates - Angular coordinates expressed in the same equatorial system as vec.

Param	Type	Description
vec	Vector	A vector in an equatorial coordinate system.

---

Astronomy.SphereFromVector(vector) ⇒ Spherical

Converts Cartesian coordinates to spherical coordinates.

Given a Cartesian vector, returns latitude, longitude, and distance.

Kind: static method of Astronomy
Returns: Spherical - Spherical coordinates that are equivalent to the given vector.

Param	Type	Description
vector	Vector	Cartesian vector to be converted to spherical coordinates.

---

Astronomy.HorizonFromVector(vector, refraction) ⇒ Spherical

Converts Cartesian coordinates to horizontal coordinates.

Given a horizontal Cartesian vector, returns horizontal azimuth and altitude.

IMPORTANT: This function differs from SphereFromVector in two ways:

• SphereFromVector returns a lon value that represents azimuth defined counterclockwise from north (e.g., west = +90), but this function represents a clockwise rotation (e.g., east = +90). The difference is because SphereFromVector is intended to preserve the vector "right-hand rule", while this function defines azimuth in a more traditional way as used in navigation and cartography.
• This function optionally corrects for atmospheric refraction, while SphereFromVector does not.

The returned object contains the azimuth in lon. It is measured in degrees clockwise from north: east = +90 degrees, west = +270 degrees.

The altitude is stored in lat.

The distance to the observed object is stored in dist, and is expressed in astronomical units (AU).

Kind: static method of Astronomy

Param	Type	Description
vector	Vector	Cartesian vector to be converted to horizontal coordinates.
refraction	string	"normal": correct altitude for atmospheric refraction (recommended). "jplhor": for JPL Horizons compatibility testing only; not recommended for normal use. null: no atmospheric refraction correction is performed.

---

Astronomy.VectorFromHorizon(sphere, time, refraction) ⇒ Vector

Given apparent angular horizontal coordinates in sphere, calculate horizontal vector.

Kind: static method of Astronomy
Returns: Vector - A vector in the horizontal system: x = north, y = west, and z = zenith (up).

Param	Type	Description
sphere	Spherical	A structure that contains apparent horizontal coordinates: lat holds the refracted azimuth angle, lon holds the azimuth in degrees clockwise from north, and dist holds the distance from the observer to the object in AU.
time	AstroTime	The date and time of the observation. This is needed because the returned vector object requires a valid time value when passed to certain other functions.
refraction	string	"normal": correct altitude for atmospheric refraction (recommended). "jplhor": for JPL Horizons compatibility testing only; not recommended for normal use. null: no atmospheric refraction correction is performed.

---

Astronomy.Refraction(refraction, altitude) ⇒ number

Calculates the amount of "lift" to an altitude angle caused by atmospheric refraction.

Given an altitude angle and a refraction option, calculates the amount of "lift" caused by atmospheric refraction. This is the number of degrees higher in the sky an object appears due to the lensing of the Earth's atmosphere.

Kind: static method of Astronomy
Returns: number - The angular adjustment in degrees to be added to the altitude angle to correct for atmospheric lensing.

Param	Type	Description
refraction	string	"normal": correct altitude for atmospheric refraction (recommended). "jplhor": for JPL Horizons compatibility testing only; not recommended for normal use. null: no atmospheric refraction correction is performed.
altitude	number	An altitude angle in a horizontal coordinate system. Must be a value between -90 and +90.

---

Astronomy.InverseRefraction(refraction, bent_altitude) ⇒ number

Calculates the inverse of an atmospheric refraction angle.

Given an observed altitude angle that includes atmospheric refraction, calculate the negative angular correction to obtain the unrefracted altitude. This is useful for cases where observed horizontal coordinates are to be converted to another orientation system, but refraction first must be removed from the observed position.

Kind: static method of Astronomy
Returns: number - The angular adjustment in degrees to be added to the altitude angle to correct for atmospheric lensing. This will be less than or equal to zero.

Param	Type	Description
refraction	string	"normal": correct altitude for atmospheric refraction (recommended). "jplhor": for JPL Horizons compatibility testing only; not recommended for normal use. null: no atmospheric refraction correction is performed.
bent_altitude	number	The apparent altitude that includes atmospheric refraction.

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Astronomy.RotateVector(rotation, vector) ⇒ Vector

Applies a rotation to a vector, yielding a rotated vector.

This function transforms a vector in one orientation to a vector in another orientation.

Kind: static method of Astronomy
Returns: Vector - A vector in the orientation specified by rotation.

Param	Type	Description
rotation	RotationMatrix	A rotation matrix that specifies how the orientation of the vector is to be changed.
vector	Vector	The vector whose orientation is to be changed.

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Astronomy.Rotation_EQJ_ECL() ⇒ RotationMatrix

Calculates a rotation matrix from equatorial J2000 (EQJ) to ecliptic J2000 (ECL).

This is one of the family of functions that returns a rotation matrix for converting from one orientation to another. Source: EQJ = equatorial system, using equator at J2000 epoch. Target: ECL = ecliptic system, using equator at J2000 epoch.

Kind: static method of Astronomy
Returns: RotationMatrix - A rotation matrix that converts EQJ to ECL.

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Astronomy.Rotation_ECL_EQJ() ⇒ RotationMatrix

Calculates a rotation matrix from ecliptic J2000 (ECL) to equatorial J2000 (EQJ).

This is one of the family of functions that returns a rotation matrix for converting from one orientation to another. Source: ECL = ecliptic system, using equator at J2000 epoch. Target: EQJ = equatorial system, using equator at J2000 epoch.

Kind: static method of Astronomy
Returns: RotationMatrix - A rotation matrix that converts ECL to EQJ.

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Astronomy.Rotation_EQJ_EQD(time) ⇒ RotationMatrix

Calculates a rotation matrix from equatorial J2000 (EQJ) to equatorial of-date (EQD).

This is one of the family of functions that returns a rotation matrix for converting from one orientation to another. Source: EQJ = equatorial system, using equator at J2000 epoch. Target: EQD = equatorial system, using equator of the specified date/time.

Kind: static method of Astronomy
Returns: RotationMatrix - A rotation matrix that converts EQJ to EQD at time.

Param	Type	Description
time	AstroTime	The date and time at which the Earth's equator defines the target orientation.

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Astronomy.Rotation_EQD_EQJ(time) ⇒ RotationMatrix

Calculates a rotation matrix from equatorial of-date (EQD) to equatorial J2000 (EQJ).

This is one of the family of functions that returns a rotation matrix for converting from one orientation to another. Source: EQD = equatorial system, using equator of the specified date/time. Target: EQJ = equatorial system, using equator at J2000 epoch.

Kind: static method of Astronomy
Returns: RotationMatrix - A rotation matrix that converts EQD at time to EQJ.

Param	Type	Description
time	AstroTime	The date and time at which the Earth's equator defines the source orientation.

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Astronomy.Rotation_EQD_HOR(time, observer) ⇒ RotationMatrix

Calculates a rotation matrix from equatorial of-date (EQD) to horizontal (HOR).

This is one of the family of functions that returns a rotation matrix for converting from one orientation to another. Source: EQD = equatorial system, using equator of the specified date/time. Target: HOR = horizontal system.

Use HorizonFromVector to convert the return value to a traditional altitude/azimuth pair.

Kind: static method of Astronomy
Returns: RotationMatrix - A rotation matrix that converts EQD to HOR at time and for observer. The components of the horizontal vector are: x = north, y = west, z = zenith (straight up from the observer). These components are chosen so that the "right-hand rule" works for the vector and so that north represents the direction where azimuth = 0.

Param	Type	Description
time	AstroTime	The date and time at which the Earth's equator applies.
observer	Observer	A location near the Earth's mean sea level that defines the observer's horizon.

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Astronomy.Rotation_HOR_EQD(time, observer) ⇒ RotationMatrix

Calculates a rotation matrix from horizontal (HOR) to equatorial of-date (EQD).

This is one of the family of functions that returns a rotation matrix for converting from one orientation to another. Source: HOR = horizontal system (x=North, y=West, z=Zenith). Target: EQD = equatorial system, using equator of the specified date/time.

Kind: static method of Astronomy
Returns: RotationMatrix - A rotation matrix that converts HOR to EQD at time and for observer.

Param	Type	Description
time	AstroTime	The date and time at which the Earth's equator applies.
observer	Observer	A location near the Earth's mean sea level that defines the observer's horizon.

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Astronomy.Rotation_HOR_EQJ(time, observer) ⇒ RotationMatrix

Calculates a rotation matrix from horizontal (HOR) to J2000 equatorial (EQJ).

This is one of the family of functions that returns a rotation matrix for converting from one orientation to another. Source: HOR = horizontal system (x=North, y=West, z=Zenith). Target: EQJ = equatorial system, using equator at the J2000 epoch.

Kind: static method of Astronomy
Returns: RotationMatrix - A rotation matrix that converts HOR to EQD at time and for observer.

Param	Type	Description
time	AstroTime	The date and time of the observation.
observer	Observer	A location near the Earth's mean sea level that defines the observer's horizon.

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Astronomy.Rotation_EQJ_HOR(time, observer) ⇒

Calculates a rotation matrix from equatorial J2000 (EQJ) to horizontal (HOR).

This is one of the family of functions that returns a rotation matrix for converting from one orientation to another. Source: EQJ = equatorial system, using the equator at the J2000 epoch. Target: HOR = horizontal system.

Use HorizonFromVector to convert the return value to a traditional altitude/azimuth pair.

Kind: static method of Astronomy
Returns: A rotation matrix that converts EQJ to HOR at time and for observer. The components of the horizontal vector are: x = north, y = west, z = zenith (straight up from the observer). These components are chosen so that the "right-hand rule" works for the vector and so that north represents the direction where azimuth = 0.

Param	Description
time	The date and time of the desired horizontal orientation.
observer	A location near the Earth's mean sea level that defines the observer's horizon.

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Astronomy.Rotation_EQD_ECL(time) ⇒ RotationMatrix

Calculates a rotation matrix from equatorial of-date (EQD) to ecliptic J2000 (ECL).

This is one of the family of functions that returns a rotation matrix for converting from one orientation to another. Source: EQD = equatorial system, using equator of date. Target: ECL = ecliptic system, using equator at J2000 epoch.

Kind: static method of Astronomy
Returns: RotationMatrix - A rotation matrix that converts EQD to ECL.

Param	Type	Description
time	AstroTime	The date and time of the source equator.

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Astronomy.Rotation_ECL_EQD(time) ⇒ RotationMatrix

Calculates a rotation matrix from ecliptic J2000 (ECL) to equatorial of-date (EQD).

This is one of the family of functions that returns a rotation matrix for converting from one orientation to another. Source: ECL = ecliptic system, using equator at J2000 epoch. Target: EQD = equatorial system, using equator of date.

Kind: static method of Astronomy
Returns: RotationMatrix - A rotation matrix that converts ECL to EQD.

Param	Type	Description
time	AstroTime	The date and time of the desired equator.

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Astronomy.Rotation_ECL_HOR(time, observer) ⇒ RotationMatrix

Calculates a rotation matrix from ecliptic J2000 (ECL) to horizontal (HOR).

This is one of the family of functions that returns a rotation matrix for converting from one orientation to another. Source: ECL = ecliptic system, using equator at J2000 epoch. Target: HOR = horizontal system.

Use HorizonFromVector to convert the return value to a traditional altitude/azimuth pair.

Kind: static method of Astronomy
Returns: RotationMatrix - A rotation matrix that converts ECL to HOR at time and for observer. The components of the horizontal vector are: x = north, y = west, z = zenith (straight up from the observer). These components are chosen so that the "right-hand rule" works for the vector and so that north represents the direction where azimuth = 0.

Param	Type	Description
time	AstroTime	The date and time of the desired horizontal orientation.
observer	Observer	A location near the Earth's mean sea level that defines the observer's horizon.

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Astronomy.Rotation_HOR_ECL(time, observer) ⇒ RotationMatrix

Calculates a rotation matrix from horizontal (HOR) to ecliptic J2000 (ECL).

This is one of the family of functions that returns a rotation matrix for converting from one orientation to another. Source: HOR = horizontal system. Target: ECL = ecliptic system, using equator at J2000 epoch.

Kind: static method of Astronomy
Returns: RotationMatrix - A rotation matrix that converts HOR to ECL.

Param	Type	Description
time	AstroTime	The date and time of the horizontal observation.
observer	Observer	The location of the horizontal observer.

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Astronomy.Constellation(ra, dec) ⇒ ConstellationInfo

Determines the constellation that contains the given point in the sky.

Given J2000 equatorial (EQJ) coordinates of a point in the sky, determines the constellation that contains that point.

Kind: static method of Astronomy
Returns: ConstellationInfo - An object that contains the 3-letter abbreviation and full name of the constellation that contains the given (ra,dec), along with the converted B1875 (ra,dec) for that point.

Param	Type	Description
ra	number	The right ascension (RA) of a point in the sky, using the J2000 equatorial system.
dec	number	The declination (DEC) of a point in the sky, using the J2000 equatorial system.

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Astronomy.SearchLunarEclipse(date) ⇒ LunarEclipseInfo

Kind: static method of Astronomy
Brief: Searches for a lunar eclipse.

This function finds the first lunar eclipse that occurs after startTime. A lunar eclipse may be penumbral, partial, or total. See LunarEclipseInfo for more information. To find a series of lunar eclipses, call this function once, then keep calling NextLunarEclipse as many times as desired, passing in the center value returned from the previous call.

Param	Type	Description
date	Date | number | AstroTime	The date and time for starting the search for a lunar eclipse.

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Astronomy.NextLunarEclipse(prevEclipseTime) ⇒ LunarEclipseInfo

Kind: static method of Astronomy
Brief: Searches for the next lunar eclipse in a series.

After using SearchLunarEclipse to find the first lunar eclipse in a series, you can call this function to find the next consecutive lunar eclipse. Pass in the center value from the LunarEclipseInfo returned by the previous call to Astronomy.SearchLunarEclipse or Astronomy.NextLunarEclipse to find the next lunar eclipse.

Param	Type	Description
prevEclipseTime	AstroTime	A date and time near a full moon. Lunar eclipse search will start at the next full moon.

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Astronomy.SearchGlobalSolarEclipse(startTime) ⇒ GlobalSolarEclipseInfo

Kind: static method of Astronomy
Brief: Searches for a solar eclipse visible anywhere on the Earth's surface.

This function finds the first solar eclipse that occurs after startTime. A solar eclipse may be partial, annular, or total. See GlobalSolarEclipseInfo for more information. To find a series of solar eclipses, call this function once, then keep calling NextGlobalSolarEclipse as many times as desired, passing in the peak value returned from the previous call.

Param	Type	Description
startTime	AstroTime	The date and time for starting the search for a solar eclipse.

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Astronomy.NextGlobalSolarEclipse(prevEclipseTime) ⇒ GlobalSolarEclipseInfo

Kind: static method of Astronomy
Brief: Searches for the next global solar eclipse in a series.

After using SearchGlobalSolarEclipse to find the first solar eclipse in a series, you can call this function to find the next consecutive solar eclipse. Pass in the peak value from the GlobalSolarEclipseInfo returned by the previous call to SearchGlobalSolarEclipse or NextGlobalSolarEclipse to find the next solar eclipse.

Param	Type	Description
prevEclipseTime	AstroTime	A date and time near a new moon. Solar eclipse search will start at the next new moon.

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Astronomy.SearchLocalSolarEclipse(startTime, observer) ⇒ LocalSolarEclipseInfo

Kind: static method of Astronomy
Brief: Searches for a solar eclipse visible at a specific location on the Earth's surface.

This function finds the first solar eclipse that occurs after startTime. A solar eclipse may be partial, annular, or total. See LocalSolarEclipseInfo for more information.

To find a series of solar eclipses, call this function once, then keep calling NextLocalSolarEclipse as many times as desired, passing in the peak value returned from the previous call.

IMPORTANT: An eclipse reported by this function might be partly or completely invisible to the observer due to the time of day. See LocalSolarEclipseInfo for more information about this topic.

Param	Type	Description
startTime	AstroTime	The date and time for starting the search for a solar eclipse.
observer	Observer	The geographic location of the observer.

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Astronomy.NextLocalSolarEclipse(prevEclipseTime, observer) ⇒ LocalSolarEclipseInfo

Kind: static method of Astronomy
Brief: Searches for the next local solar eclipse in a series.

After using SearchLocalSolarEclipse to find the first solar eclipse in a series, you can call this function to find the next consecutive solar eclipse. Pass in the peak value from the LocalSolarEclipseInfo returned by the previous call to SearchLocalSolarEclipse or NextLocalSolarEclipse to find the next solar eclipse. This function finds the first solar eclipse that occurs after startTime. A solar eclipse may be partial, annular, or total. See LocalSolarEclipseInfo for more information.

Param	Type	Description
prevEclipseTime	AstroTime	The date and time for starting the search for a solar eclipse.
observer	Observer	The geographic location of the observer.

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Astronomy.SearchTransit(body, startTime) ⇒ TransitInfo

Kind: static method of Astronomy
Brief: Searches for the first transit of Mercury or Venus after a given date.

Finds the first transit of Mercury or Venus after a specified date. A transit is when an inferior planet passes between the Sun and the Earth so that the silhouette of the planet is visible against the Sun in the background. To continue the search, pass the finish time in the returned structure to NextTransit.

Param	Type	Description
body	string	The planet whose transit is to be found. Must be "Mercury" or "Venus".
startTime	AstroTime	The date and time for starting the search for a transit.

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Astronomy.NextTransit(body, prevTransitTime) ⇒ TransitInfo

Kind: static method of Astronomy
Brief: Searches for another transit of Mercury or Venus.

After calling SearchTransit to find a transit of Mercury or Venus, this function finds the next transit after that. Keep calling this function as many times as you want to keep finding more transits.

Param	Type	Description
body	string	The planet whose transit is to be found. Must be "Mercury" or "Venus".
prevTransitTime	AstroTime	A date and time near the previous transit.

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Astronomy.ContinuousFunction ⇒ number

A continuous function of time used in a call to the Search function.

Kind: static typedef of Astronomy

Param	Type	Description
t	AstroTime	The time at which to evaluate the function.

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Astronomy.SearchOptions : Object

Options for the Search function.

Kind: static typedef of Astronomy
Properties

Name	Type	Description
dt_tolerance_seconds	number | null	The number of seconds for a time window smaller than which the search is considered successful. Using too large a tolerance can result in an inaccurate time estimate. Using too small a tolerance can cause excessive computation, or can even cause the search to fail because of limited floating-point resolution. Defaults to 1 second.
init_f1	number | null	As an optimization, if the caller of Search has already calculated the value of the function being searched (the parameter func) at the time coordinate t1, it can pass in that value as init_f1. For very expensive calculations, this can measurably improve performance.
init_f2	number | null	The same as init_f1, except this is the optional initial value of func(t2) instead of func(t1).

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