FindAstroEvent

FindAstroEvent[etype]

gives the date of the next astro event of type etype.

FindAstroEvent[etype,date]

gives the next astro event following the given date.

FindAstroEvent[etype,date,loc]

gives the date of the next astro event as observed from the location loc.

Details and Options

  • Find precise dates for astronomical events such as moon phases, conjunctions, oppositions and various other types of alignments.
  • In FindAstroEvent[etype,…], possible event types etype related to solar solstices and equinoxes for Earth include:
  • "MarchEquinox"equinox when the Sun has ecliptic longitude 0°
    "JuneSolstice"solstice when the Sun has ecliptic longitude 90°
    "SeptemberEquinox"equinox when the Sun has ecliptic longitude 180°
    "DecemberSolstice"solstice when the Sun has ecliptic longitude 270°
  • Event types related to moon phases include:
  • "NewMoon"new moon for Earth's Moon
    "FullMoon"full moon for Earth's Moon
    {"MoonPhase",phase}instant of phase for Earth's Moon
    {"NewMoon",moon}new moon for moon, as observed from its central body
    {"FullMoon",moon}full moon for moon, as observed from its central body
    {"MoonPhase",moon,phase}instant of phase for moon, as observed from its central body
  • Event types related to rise/set/culmination observations include:
  • "Sunrise"sunrise
    "Sunset"sunset
    "FirstEquilux"day in the first half of the year with equal day and night
    "SecondEquilux"day in the second half or the year with equal day and night
    "Moonrise"Earth's Moon rise
    "Moonset"Earth's Moon set
    {"Rise",body}rise of the given body
    {"Set",body}set of the given body
    {"UpperCulmination",body}upper culmination of a body
    {"LowerCulmination",body}lower culmination of a body
  • Event types related to close alignments include:
  • {"Conjunction",body1,body2}conjunction of two bodies in a longitude coordinate
    {"InferiorConjunction",body}the body passes between the Sun and the observer
    {"SuperiorConjunction",body}the body passes behind the Sun
    {"Conjunction",body}inferior or superior conjunction of a body with the Sun
    {"Opposition",body}opposition of a body and the Sun
  • Event types related to quadratures and greatest elongations include:
  • {"EasternQuadrature",body}eastern quadrature of a solar system outer body
    {"WesternQuadrature",body}western quadrature of a solar system outer body
    {"GreatestEasternElongation",body}greatest eastern elongation of an inner body
    {"GreatestWesternElongation",body}greatest western elongation of an inner body
  • Event types related to physical distance include:
  • {"Distance",body1,body2,cond}distance between body1 and body2 obeys condition cond
    {"Distance",body1,body2,cond,adjst}distance condition extended by adjst
    {"Periapsis",body}local mininum of distance of body orbiting its center
    {"Apoapsis",body}local maximum of distance of body orbiting its center
  • Event types related to angular separation include:
  • {"Separation",body1,body2,cond}angle between body1 and body2 obeys condition cond
    {"Separation",body1,body2,cond,adjst}angular condition extended by adjst
    {"Appulse",body1,body2}local mininum of angular separation between two bodies
    {"Appulse",body}local minimum of separation between body and the Sun
  • Possible conditions cond include:
  • Quantity[…]exact value of quantity, in appropriate units
    GreaterThan[val]quantity is larger than value val
    "GlobalMaximum"global maximum of quantity
    "LocalMaximum"list of local maxima of quantity
  • Minima and maxima conditions can be adjusted to return the date intervals where values differed from the extrema by less than the given adjustment values.

Examples

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Basic Examples  (2)

Find the instant of the next March equinox:

On this date, the Sun has ecliptic longitude exactly 0° or equivalently, 360°:

Find the next conjunction of Mars with the Sun:

Show Mars having the same ecliptic longitude as the center of the Sun on this date:

Scope  (24)

Equinox and Solstice Events  (2)

Find the date of the next March equinox, the beginning of spring in the Northern Hemisphere:

Find all March equinoxes in the twentieth century, in the GMT time zone:

They fall on one of these March days:

Rise, Set, Culmination and Equilux Events  (3)

Find the next rise of the Moon, as observed from your location:

That syntax is an abbreviation of this more general form:

Find the next instant when Jupiter sets:

Find the next instant when the Moon crosses your local meridian:

Find the next instant of "solar midnight":

Find the next upper culmination of Phobos as observed from Olympus Mons, on the surface of Mars:

At that instant, the azimuth of Phobos will be 180 degrees:

Find the day in the first half of 2025 in which day and night will each take about 12 hours in San Jose:

Find the day in the second half of 2025 in which the same thing will happen:

Conjunction, Opposition, Quadrature and Elongation Events  (4)

Find the next conjunction of Jupiter with the Sun:

Find the next opposition of Jupiter with respect to the Sun:

Find the next western quadrature of Jupiter:

Find the next eastern quadrature of Jupiter:

Find the next inferior conjunction of Venus with the Sun:

Find the next greatest western elongation of Venus:

Find the next superior conjunction of Venus:

Find the next greatest eastern elongation of Venus:

Find the next conjunction of Venus and Jupiter, as observed from Earth:

They will have the same ecliptic longitude on that instant:

Find the inferior conjunction of the Earth with the Sun in 2031, as observed from Mars:

The Moon and Earth will appear separated by approximately the angular radius of the Sun on that date:

Distance Events  (6)

Find the next local maximum of distance between the Earth and the Moon:

This is also known as an apogee of the Moon:

The event of minimum distance between a orbiting body and its orbit center is called the periapsis:

For a body orbiting the Sun, the periapsis is also known as the perihelion:

For a body orbiting the Earth, the periapsis is also know as the perigee:

For bodies orbiting other major bodies of the solar system, the periapsis also has special names:

The event of maximum distance between a orbiting body and its orbit center is called the apoapsis:

For a body orbiting the Sun, the apoapsis is also known as the aphelion:

For a body orbiting the Earth, the apoapsis is also know as the apogee:

For bodies orbiting other major bodies of the solar system, the apoapsis also has special names:

Find the local maxima of distance between the Earth and the Moon during year 2024:

Compute the actual distances between the body centers at those instants:

Find the global minimum of distance between Saturn and the Earth between years 2020 and 2050:

Find the date interval during which the Moon was farther than 400,000 km from the Earth in July 2024:

Angular Separation Events  (5)

Find the global minimum angular distance between Jupiter and Saturn in the year 2020:

Show the relative position of the planets and their moons at that moment, on an arcminute grid:

Find the local minima of angular separation between Jupiter and Saturn in the years 2010 to 2035:

Plot the angular separation between the two planets, with grid lines at the positions of the local minima:

Find the minimal angular separation between the Sun and the Moon in April 2024:

There was a total solar eclipse on that date:

Find the maximal angular separation between the Sun and the Moon in September 2024:

There was a lunar eclipse on that date:

Find the global minimum of separation between Venus and the Sun, as observed from Earth in 2010–2015:

This was an instant of transit of Venus in front of the Sun:

Date Specifications  (4)

Find the next March equinox after a given date:

Find the June solstices during a given date interval:

Find the September equinoxes after each date in a list of dates:

The normal form of the event series is a list of date pairs:

If the event type defines a continuous period of time, the result will be a date interval:

The date interval may contain several disconnected subintervals:

These are the instants at which the condition ceases to be obeyed:

Options  (7)

CalendarType  (2)

FindAstroEvent returns dates in the Gregorian calendar by default:

Return dates in the French Revolutionary calendar, in which the year started on the September equinox:

At the beginning of the Common Era, the March equinox was around March 22 in the Julian calendar:

By the beginning of 1582, the March equinox had drifted to March 10 in the Julian calendar:

After the Gregorian reform in October 1582, the March equinox went back to March 21:

DateFormat  (1)

FindAstroEvent returns dates in a long format by default:

Specify your own format:

DateGranularity  (1)

FindAstroEvent returns dates with granularity "Instant" by default:

Return dates with "Day" granularity:

TimeDirection  (1)

FindAstroEvent finds the next event of the given type by default:

Find the previous event:

TimeSystem  (1)

FindAstroEvent returns dates in universal time by default:

Return dates in "TT" time instead:

TimeZone  (1)

FindAstroEvent returns dates in your local time zone by default:

Return dates in the GMT time zone:

Applications  (3)

Find all solstices and equinoxes in the 2020s, reported in the GMT time zone:

Show the sequence of conjunctions, oppositions and quadratures of Jupiter for the next few years:

Show the results in a Tabular object:

Visualize those dates in a timeline:

Construct a function that computes the date of a Voyager flyby and plots distance in units of 1000 km for a few hours around the event, with the central body represented in brown color:

Voyager 1 was launched on September 5, 1977, and first visited Jupiter's system on March 5, 1979:

Then it visited Saturn's system on November 12 and 13, 1980, getting very close to Titan:

Voyager 2 was launched two weeks before Voyager 1 but reached Jupiter later, on July 9, 1979:

Then it visited Saturn's system on August 26, 1981:

Then Uranus on January 24, 1986:

And then Neptune on August 25, 1989, passing very close to the planet's surface:

Properties & Relations  (10)

NewMoon[date] is equivalent to FindAstroEvent["NewMoon",date]:

FullMoon[date] is equivalent to FindAstroEvent["FullMoon",date]:

MoonPhaseDate[date,phase] is equivalent to FindAstroEvent[{"MoonPhase",phase},date]:

Use a numeric specification of phase:

Sunrise[loc,date] is equivalent to FindAstroEvent["Sunrise",date,loc]:

Sunset[loc,date] is equivalent to FindAstroEvent["Sunset",date,loc]:

For rise/set event types, AstroRiseSet[body,type,loc,date] is equivalent to FindAstroEvent[{type,body},date,loc]:

The first and last quarters of the Moon correspond to eastern and western quadratures:

New moons are conjunctions of the Moon, while full moons are oppositions of the Moon:

Find the instant of the next March equinox:

On this date, the Sun has ecliptic longitude exactly 0° or equivalently, 360°:

Its ecliptic latitude will be very close to zero, and the subsolar point will also be very close to the equator:

At the instant of the March equinox, the Sun is approximately above Earth's equator:

But that does not imply equal duration of day and night, even for locations close to the equator:

A day with approximately equal day and night durations for a given location is called an equilux:

A conjunction is defined by coincidence of ecliptic longitudes:

An appulse is defined by a local minimum of angular separation, and there will be one in the vicinity:

On the instant of conjunction, the ecliptic longitudes coincide, but not on the instant of appulse:

However, the angular distance between the planets is minimal on the instant of appulse:

Wolfram Research (2025), FindAstroEvent, Wolfram Language function, https://reference.wolfram.com/language/ref/FindAstroEvent.html.

Text

Wolfram Research (2025), FindAstroEvent, Wolfram Language function, https://reference.wolfram.com/language/ref/FindAstroEvent.html.

CMS

Wolfram Language. 2025. "FindAstroEvent." Wolfram Language & System Documentation Center. Wolfram Research. https://reference.wolfram.com/language/ref/FindAstroEvent.html.

APA

Wolfram Language. (2025). FindAstroEvent. Wolfram Language & System Documentation Center. Retrieved from https://reference.wolfram.com/language/ref/FindAstroEvent.html

BibTeX

@misc{reference.wolfram_2024_findastroevent, author="Wolfram Research", title="{FindAstroEvent}", year="2025", howpublished="\url{https://reference.wolfram.com/language/ref/FindAstroEvent.html}", note=[Accessed: 15-January-2025 ]}

BibLaTeX

@online{reference.wolfram_2024_findastroevent, organization={Wolfram Research}, title={FindAstroEvent}, year={2025}, url={https://reference.wolfram.com/language/ref/FindAstroEvent.html}, note=[Accessed: 15-January-2025 ]}