Astro v0.2.0 Astro View Source

Functions for basic astronomical observations such as sunrise, sunset, solstice, equinox, moonrise, moonset and moon phase.

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Functions

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

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

Calculates the sunrise for a given location and date.

Calculates the sunset for a given location and date.

Link to this section Types

Link to this section Functions

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equinox(year, event)

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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.

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solstice(year, event)

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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.

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sunrise(location, date, options \\ default_options())

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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 Date.t, NaiveDateTime.t or DateTime.t 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}
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sunset(location, date, options \\ default_options())

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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 Date.t, NaiveDateTime.t or DateTime.t 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 DateTime.t 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}