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.
Quick Start
To get started quickly, here are some browser scripting examples and some Node.js examples.
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. |
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. |
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. |
API Reference
Astronomy : object
Kind: global namespace
Astronomy.PerformanceInfo
Holds performance metrics for developers to optimize execution speed. Most users can safely ignore this class.
Kind: static class of Astronomy
Properties
| Name | Type | Description |
|---|---|---|
| search_func | number |
Number of times Search called a func passed to it. |
| search | number |
Number of times Search was called. |
| longitude_search | number |
Number of times SearchRelativeLongitude was called. |
| longitude_iter | number |
The total number of iterations executed inside SearchRelativeLongitude. |
| lunar_apsis_calls | number |
The number of times SearchLunarApsis was called. |
| lunar_apsis_iter | number |
The number of search iterations inside SearchLunarApsis. |
| calcmoon | number |
The number of times the Moon's position was calculated. (This is an expensive operation.) |
performanceInfo.Clone() ⇒ PerformanceInfo
Creates a copy of a PerformanceInfo object.
This allows us to create a snapshot of the performance metrics
that can be handed back to outside code that will not change
as the Astronomy code continues to execute and change the metrics.
Kind: instance method of PerformanceInfo
Astronomy.AstroTime
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.
Kind: static class of Astronomy
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. |
new AstroTime(date)
| Param | Type | Description |
|---|---|---|
| date | Date | number |
A JavaScript Date object or a numeric UTC value expressed in J2000 days. |
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
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. |
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. |
vector.Length() ⇒ number
Returns the length of the vector in astronomical units (AU).
Kind: instance method of Vector
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). |
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. |
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. |
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_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. |
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. |
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. |
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. |
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. |
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]. |
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
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. |
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
Astronomy.GetPerformanceMetrics() ⇒ PerformanceInfo
Takes a snapshot of the current state of the performance metrics. The metrics inside the returned object will not change and can be retained by calling code to be compared with later snapshots.
Kind: static method of Astronomy
Astronomy.ResetPerformanceMetrics()
Resets the internal performance metrics back to their initial states. You can call this before starting a new series of performance tests.
Kind: static method of Astronomy
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. |
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", or "Pluto". |
| date | Date | number | AstroTime |
The date and time for which the body's position is to be calculated. |
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.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. |
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). |