@spec date_time_lunar_phase_at_or_after(date(), phase()) :: {:ok, Calendar.datetime()}

Returns the date time of a given lunar phase at or after a given date time or date.

Arguments

• date_time is a DateTime or a Date or any struct that meets the requirements of t:Calendar.date or t:Calendar.datetime

• phase is the required lunar phase expressed as a float number of degrees between 0.0 and 360.0

Returns

• {:ok, date_time} at which the phase occurs or

• {:error, {module, reason}}

Example

iex> Astro.date_time_lunar_phase_at_or_after(~D[2021-08-01], Astro.Lunar.full_moon())
{:ok, ~U[2021-08-22 12:01:02.000000Z]}

@spec date_time_lunar_phase_at_or_before(date(), phase()) ::
  {:ok, Calendar.datetime()}

Returns the date time of a given lunar phase at or before a given date time or date.

Arguments

• date_time is a DateTime or a Date or any struct that meets the requirements of t:Calendar.date or t:Calendar.datetime

• phase is the required lunar phase expressed as a float number of degrees between 0 and 3660

Returns

• {:ok, date_time} at which the phase occurs or

• {:error, {module, reason}}

Example

iex> Astro.date_time_lunar_phase_at_or_before(~D[2021-08-01], Astro.Lunar.new_moon())
{:ok, ~U[2021-07-10 01:15:33.000000Z]}

@spec date_time_new_moon_at_or_after(date()) :: {:ok, Calendar.datetime()}

Returns the date time of the new moon at or after a given date or date time.

Arguments

• date_time is a DateTime or a Date or any struct that meets the requirements of t:Calendar.date or t:Calendar.datetime

Returns

• {:ok, date_time} at which the new moon occurs or

• {:error, {module, reason}}

Example

iex> Astro.date_time_new_moon_at_or_after ~D[2021-08-23]
{:ok, ~U[2021-09-07 00:50:43.000000Z]}

@spec date_time_new_moon_before(date()) :: {:ok, Calendar.datetime()}

Returns the date time of the new moon before a given date or date time.

Arguments

• date_time is a DateTime or a Date or any struct that meets the requirements of t:Calendar.date or t:Calendar.datetime

Returns

• {:ok, date_time} at which the new moon occurs or

• {:error, {module, reason}}

Example

iex> Astro.date_time_new_moon_before ~D[2021-08-23]
{:ok, ~U[2021-08-08 13:49:07.000000Z]}

@spec declination(Astro.Time.moment(), angle(), angle()) :: angle()

beta and lambda in degrees

@spec equinox(Calendar.year(), :march | :september) :: {:ok, DateTime.t()}

Returns the datetime in UTC for either the March or September equinox.

Arguments

• year is the gregorian year for which the equinox is to be calculated

• event is either :march or :september indicating which of the two annual equinox datetimes is required

Returns

• {:ok, datetime} representing the UTC datetime of the equinox

Examples

iex> Astro.equinox 2019, :march
{:ok, ~U[2019-03-20 21:58:06Z]}
iex> Astro.equinox 2019, :september
{:ok, ~U[2019-09-23 07:49:30Z]}

Notes

This equinox calculation is expected to be accurate to within 2 minutes for the years 1000 CE to 3000 CE.

An equinox is commonly regarded as the instant of time when the plane of Earth's equator passes through the center of the Sun. This occurs twice each year: around 20 March and 23 September.

In other words, it is the moment at which the center of the visible Sun is directly above the equator.

@spec hours_of_daylight(location(), Calendar.date()) :: {:ok, Time.t()}

Returns the number of hours of daylight for a given location on a given date.

Arguments

• location is the latitude, longitude and optionally elevation for the desired hours of daylight. It can be expressed as:

  • {lng, lat} - a tuple with longitude and latitude as floating point numbers. Note the order of the arguments.
  • a Geo.Point.t struct to represent a location without elevation
  • a Geo.PointZ.t struct to represent a location and elevation

• date is any date in the Gregorian calendar (for example, Calendar.ISO)

Returns

• {:ok, time} where time is a Time.t()

Examples

iex> Astro.hours_of_daylight {151.20666584, -33.8559799094}, ~D[2019-12-07]
{:ok, ~T[14:18:45]}

# No sunset in summer
iex> Astro.hours_of_daylight {-62.3481, 82.5018}, ~D[2019-06-07]
{:ok, ~T[23:59:59]}

# No sunrise in winter
iex> Astro.hours_of_daylight {-62.3481, 82.5018}, ~D[2019-12-07]
{:ok, ~T[00:00:00]}

Notes

In latitudes above the polar circles (approximately +/- 66.5631 degrees) there will be no hours of daylight in winter and 24 hours of daylight in summer.

@spec illuminated_fraction_of_moon_at(date()) :: number()

Returns the illumination of the moon as a fraction for a given date or date time.

Arguments

• date_time is a DateTime or a Date or any struct that meets the requirements of t:Calendar.date or t:Calendar.datetime

Returns

• a float value between 0.0 and 1.0 representing the fractional illumination of the moon.

Example

iex> Astro.illuminated_fraction_of_moon_at(~D[2017-03-16])
0.8884442367681415

iex> Astro.illuminated_fraction_of_moon_at(~D[1992-04-12])
0.6786428237168787

@spec lunar_phase_at(date()) :: phase()

Returns the lunar phase as a float number of degrees at a given date or date time.

Arguments

• date_time is a DateTime, Date or a moment which is a float number of days since 0000-01-01

Returns

• the lunar phase as a float number of degrees.

Example

iex> Astro.lunar_phase_at ~U[2021-08-22 12:01:02.170362Z]
180.00001498208536

iex> Astro.lunar_phase_at(~U[2021-07-10 01:18:25.422335Z])
0.021567106773019873

@spec lunar_phase_emoji(phase()) :: String.t()

Returns the moon phase as a UTF8 binary representing an emoji of the moon phase.

Arguments

• phase is a moon phase between 0.0 and 360.0

Returns

• A single grapheme string representing the Unicode moon phase emoji

Examples

iex> Astro.lunar_phase_emoji 0
"🌑"
iex> Astro.lunar_phase_emoji 45
"🌒"
iex> Astro.lunar_phase_emoji 90
"🌓"
iex> Astro.lunar_phase_emoji 135
"🌔"
iex> Astro.lunar_phase_emoji 180
"🌕"
iex> Astro.lunar_phase_emoji 245
"🌖"
iex> Astro.lunar_phase_emoji 270
"🌗"
iex> Astro.lunar_phase_emoji 320
"🌘"
iex> Astro.lunar_phase_emoji 360
"🌑"

iex> ~U[2021-08-22 12:01:02.170362Z]
...> |> Astro.lunar_phase_at()
...> |> Astro.lunar_phase_emoji()
"🌕"

@spec moon_position_at(date()) :: Geo.PointZ.t()

Returns a t:Geo.PointZ containing the right ascension and declination of the moon at a given date or date time.

Arguments

• date_time is a DateTime or a Date or any struct that meets the requirements of t:Calendar.date or t:Calendar.datetime

Returns

• a t:Geo.PointZ struct with coordinates {right_ascension, declination, distance} with properties %{reference: :celestial, object: :moon} distance is in meters.

Example

iex> Astro.moon_position_at(~D[1992-04-12]) |> Astro.Location.round(6)
%Geo.PointZ{
  coordinates: {134.697888, 13.765243, 5.511320224169038e19},
  properties: %{object: :moon, reference: :celestial},
  srid: nil
}

@spec right_ascension(Astro.Time.moment(), angle(), angle()) :: angle()

beta and lambda in degrees

@spec solar_noon(location(), Calendar.date()) :: {:ok, DateTime.t()}

Returns solar noon for a given date and location as a UTC datetime

Arguments

• location is the latitude, longitude and optionally elevation for the desired solar noon time. It can be expressed as:

  • {lng, lat} - a tuple with longitude and latitude as floating point numbers. Note the order of the arguments.
  • a Geo.Point.t struct to represent a location without elevation
  • a Geo.PointZ.t struct to represent a location and elevation

• date is any date in the Gregorian calendar (for example, Calendar.ISO)

Returns

• a UTC datetime representing solar noon at the given location for the given date

Example

iex> Astro.solar_noon {151.20666584, -33.8559799094}, ~D[2019-12-06]
{:ok, ~U[2019-12-06 01:45:42Z]}

Notes

Solar noon is the moment when the Sun passes a location's meridian and reaches its highest position in the sky. In most cases, it doesn't happen at 12 o'clock.

At solar noon, the Sun reaches its highest position in the sky as it passes the local meridian.

@spec solstice(Calendar.year(), :june | :december) :: {:ok, DateTime.t()}

Returns the datetime in UTC for either the June or December solstice.

Arguments

• year is the gregorian year for which the solstice is to be calculated

• event is either :june or :december indicating which of the two annual solstice datetimes is required

Returns

• {:ok, datetime} representing the UTC datetime of the solstice

Examples

iex> Astro.solstice 2019, :december
{:ok, ~U[2019-12-22 04:18:57Z]}
iex> Astro.solstice 2019, :june
{:ok, ~U[2019-06-21 15:53:45Z]}

Notes

This solstice calculation is expected to be accurate to within 2 minutes for the years 1000 CE to 3000 CE.

A solstice is an event occurring when the Sun appears to reach its most northerly or southerly excursion relative to the celestial equator on the celestial sphere. Two solstices occur annually, around June 21 and December 21.

The seasons of the year are determined by reference to both the solstices and the equinoxes.

The term solstice can also be used in a broader sense, as the day when this occurs. The day of a solstice in either hemisphere has either the most sunlight of the year (summer solstice) or the least sunlight of the year (winter solstice) for any place other than the Equator.

Alternative terms, with no ambiguity as to which hemisphere is the context, are "June solstice" and "December solstice", referring to the months in which they take place every year.

@spec sun_apparent_longitude(Calendar.date()) :: degrees()

Returns solar longitude for a given date. Solar longitude is used to identify the seasons.

Arguments

• date is any date in the Gregorian calendar (for example, Calendar.ISO)

Returns

• a float number of degrees between 0 and 360 representing the solar longitude on date

Examples

iex> Astro.sun_apparent_longitude ~D[2019-03-21]
0.08035853207991295
iex> Astro.sun_apparent_longitude ~D[2019-06-22]
90.32130455695378
iex> Astro.sun_apparent_longitude ~D[2019-09-23]
179.68691978440197
iex> Astro.sun_apparent_longitude ~D[2019-12-23]
270.83941087483504

Notes

Solar longitude (the ecliptic longitude of the sun) in effect describes the position of the earth in its orbit, being zero at the moment of the vernal equinox.

Since it is based on how far the earth has moved in its orbit since the equinox, it is a measure of what time of the tropical year (the year of seasons) we are in, but without the inaccuracies of a calendar date, which is perturbed by leap years and calendar imperfections.

@spec sun_azimuth_elevation(location(), Calendar.datetime()) ::
  {azimuth :: float(), altitude :: float()}

Returns a tuple {azimuth, altitude} for a given date time and location.

Arguments

• location is the latitude, longitude and optionally elevation for the desired sunrise azimuth and altitude. It can be expressed as:

  • {lng, lat} - a tuple with longitude and latitude as floating point numbers. Note the order of the arguments.
  • a Geo.Point.t struct to represent a location without elevation
  • a Geo.PointZ.t struct to represent a location and elevation

• date_time is a DateTime any struct that meets the requirements of t:Calendar.datetime.

Returns

• a tuple of the format {azimith, altitude} which are expressed in float degrees.

Example

iex> {:ok, date_time} = DateTime.new(~D[2023-05-17], ~T[12:47:00], "Australia/Sydney")
iex> location = {151.1637781, -33.5145852}
iex> {_azimuth, _altitude} = Astro.sun_azimuth_elevation(location, date_time)

@spec sun_position_at(date()) :: Geo.PointZ.t()

Returns a t:Geo.PointZ containing the right ascension and declination of the sun at a given date or date time.

Arguments

• date_time is a DateTime or a Date or any struct that meets the requirements of t:Calendar.date or t:Calendar.datetime

Returns

• a t:Geo.PointZ struct with coordinates {right_ascension, declination, distance} with properties %{reference: :celestial, object: :sun}. distance is in meters.

Example

iex> Astro.sun_position_at(~D[1992-10-13])
%Geo.PointZ{
  coordinates: {-161.6185428539835, -7.785325031528879, 149169604711.3518},
  properties: %{object: :sun, reference: :celestial},
  srid: nil
}

@spec sunrise(location(), date(), options()) ::
  {:ok, DateTime.t()} | {:error, :time_zone_not_found | :no_time}

Calculates the sunrise for a given location and date.

Sunrise is the moment when the upper limb of the sun appears on the horizon in the morning.

Arguments

• location is the latitude, longitude and optionally elevation for the desired sunrise time. It can be expressed as:

  • {lng, lat} - a tuple with longitude and latitude as floating point numbers. Note the order of the arguments.
  • a Geo.Point.t struct to represent a location without elevation
  • a Geo.PointZ.t struct to represent a location and elevation

• date is a t:Date, t:NaiveDateTime or t:DateTime to indicate the date of the year in which the sunrise time is required.

• options is a keyword list of options.

Options

• solar_elevation represents the type of sunrise required. The default is :geometric which equates to a solar elevation of 90°. In this case the calulation also accounts for refraction and elevation to return a result which accords with the eyes perception. Other solar elevations are:

  • :civil representing a solar elevation of 96.0°. At this point the sun is just below the horizon so there is generally enough natural light to carry out most outdoor activities.

  • :nautical representing a solar elevation of 102.0° This is the point at which the horizon is just barely visible and the moon and stars can still be used for navigation.

  • :astronomicalrepresenting a solar elevation of 108.0°. This is the point beyond which astronomical observation becomes impractical.

  • Any floating point number representing the desired solar elevation.

• :time_zone is the time zone to in which the sunrise is requested. The default is :default in which the sunrise time is reported in the time zone of the requested location. Any other time zone name supported by the option :time_zone_database is acceptabe.

• :time_zone_database represents the module that implements the Calendar.TimeZoneDatabase behaviour. The default is Tzdata.TimeZoneDatabase.

Returns

• a DateTime.t representing the time of sunrise in the requested timzone at the requested location or

• {:error, :time_zone_not_found} if the requested time zone is unknown

• {:error, :no_time} if for the requested date and location there is no sunrise. This can occur at very high latitudes during summer and winter.

Examples

# Sunrise in Sydney, Australia
Astro.sunrise({151.20666584, -33.8559799094}, ~D[2019-12-04])
{:ok, #DateTime<2019-12-04 05:37:00.000000+11:00 AEDT Australia/Sydney>}

# Sunrise in Alert, Nanavut, Canada
Astro.sunrise({-62.3481, 82.5018}, ~D[2019-12-04])
{:error, :no_time}

@spec sunset(location(), date(), options()) ::
  {:ok, DateTime.t()} | {:error, :time_zone_not_found | :no_time}

Calculates the sunset for a given location and date.

Sunset is the moment when the upper limb of the sun disappears below the horizon in the evening.

Arguments

• location is the latitude, longitude and optionally elevation for the desired sunrise time. It can be expressed as:

  • {lng, lat} - a tuple with longitude and latitude as floating point numbers. Note the order of the arguments.
  • a Geo.Point.t struct to represent a location without elevation
  • a Geo.PointZ.t struct to represent a location and elevation

• date is a t:Date, t:NaiveDateTime or t:DateTime to indicate the date of the year in which the sunset time is required.

• options is a keyword list of options.

Options

• solar_elevation represents the type of sunset required. The default is :geometric which equates to a solar elevation of 90°. In this case the calulation also accounts for refraction and elevation to return a result which accords with the eyes perception. Other solar elevations are:

  • :civil representing a solar elevation of 96.0°. At this point the sun is just below the horizon so there is generally enough natural light to carry out most outdoor activities.

  • :nautical representing a solar elevation of 102.0° This is the point at which the horizon is just barely visible and the moon and stars can still be used for navigation.

  • :astronomicalrepresenting a solar elevation of 108.0°. This is the point beyond which astronomical observation becomes impractical.

  • Any floating point number representing the desired solar elevation.

• :time_zone is the time zone to in which the sunset is requested. The default is :default in which the sunset time is reported in the time zone of the requested location. Any other time zone name supported by the option :time_zone_database is acceptabe.

• :time_zone_database represents the module that implements the Calendar.TimeZoneDatabase behaviour. The default is Tzdata.TimeZoneDatabase.

Returns

• a t:DateTime representing the time of sunset in the requested time zone at the requested location or

• {:error, :time_zone_not_found} if the requested time zone is unknown

• {:error, :no_time} if for the requested date and location there is no sunset. This can occur at very high latitudes during summer and winter.

Examples

# Sunset in Sydney, Australia
Astro.sunset({151.20666584, -33.8559799094}, ~D[2019-12-04])
{:ok, #DateTime<2019-12-04 19:53:00.000000+11:00 AEDT Australia/Sydney>}

# Sunset in Alert, Nanavut, Canada
Astro.sunset({-62.3481, 82.5018}, ~D[2019-12-04])
{:error, :no_time}