defmodule Astro do
@moduledoc """
Functions for basic astronomical observations such
as sunrise, sunset, solstice, equinox, moonrise,
moonset and moon phase.
"""
alias Astro.{Solar, Lunar, Location, Time, Math, Guards}
import Astro.Math, only: [
sin: 1,
cos: 1,
atan_r: 2,
tan: 1,
mod: 2,
to_degrees: 1
]
import Astro.Solar, only: [
obliquity_correction: 1
]
@type longitude :: float()
@type latitude :: float()
@type altitude :: float()
@type degrees :: float()
@type angle() :: number()
@type meters() :: number()
@type phase() :: angle()
@type location :: {longitude, latitude} | Geo.Point.t() | Geo.PointZ.t()
@type date :: Calendar.date() | Calendar.datetime()
@type options :: keyword()
defguard is_lunar_phase(phase) when phase >= 0.0 and phase <= 360.0
@doc """
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)
"""
# Use https://midcdmz.nrel.gov/solpos/spa.html for validation
# current implementation is approx 1 degree at variance with
# that calculator.
@doc since: "0.11.0"
@spec sun_azimuth_elevation(location(), Calendar.datetime()) :: {azimuth :: float, altitude :: float}
def sun_azimuth_elevation(location, unquote(Guards.datetime()) = date_time) do
_ = calendar
%Geo.PointZ{coordinates: {right_ascension, declination, _distance}} =
sun_position_at(date_time)
%Geo.PointZ{coordinates: {_longitude, latitude, _altitude}} =
Location.normalize_location(location)
local_sidereal_time =
Time.local_sidereal_time(location, date_time)
hour_angle =
mod(local_sidereal_time - right_ascension, 360.0)
altitude =
:math.asin(sin(declination) * sin(latitude) + cos(declination) * cos(latitude) * cos(hour_angle))
|> to_degrees
a =
:math.acos((sin(declination) - sin(altitude) * sin(latitude)) / (cos(altitude) * cos(latitude)))
|> to_degrees()
azimuth =
if sin(hour_angle) < 0.0, do: a, else: 360.0 - a
{azimuth, altitude}
end
@doc """
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
}
"""
@doc since: "0.6.0"
@spec sun_position_at(date()) :: Geo.PointZ.t()
def sun_position_at(unquote(Guards.datetime()) = date_time) do
_ = calendar
date_time
|> Time.date_time_to_moment()
|> Solar.solar_position()
|> convert_distance_to_m()
|> Location.normalize_location()
|> Map.put(:properties, %{reference: :celestial, object: :sun})
end
def sun_position_at(unquote(Guards.date()) = date) do
_ = calendar
date
|> Date.to_gregorian_days()
|> Solar.solar_position()
|> convert_distance_to_m()
|> Location.normalize_location()
|> Map.put(:properties, %{reference: :celestial, object: :sun})
end
defp convert_distance_to_m({lng, lat, alt}) do
{lng, lat, Math.au_to_m(alt)}
end
@doc """
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
}
"""
@doc since: "0.6.0"
@spec moon_position_at(date()) :: Geo.PointZ.t()
def moon_position_at(unquote(Guards.datetime()) = date_time) do
_ = calendar
date_time
|> Time.date_time_to_moment()
|> Lunar.lunar_position()
|> convert_distance_to_m()
|> Location.normalize_location()
|> Map.put(:properties, %{reference: :celestial, object: :moon})
end
def moon_position_at(unquote(Guards.date()) = date) do
_ = calendar
date
|> Date.to_gregorian_days()
|> Lunar.lunar_position()
|> convert_distance_to_m()
|> Location.normalize_location()
|> Map.put(:properties, %{reference: :celestial, object: :moon})
end
@doc """
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
"""
@doc since: "0.6.0"
@spec illuminated_fraction_of_moon_at(date()) :: number()
def illuminated_fraction_of_moon_at(unquote(Guards.datetime()) = date_time) do
_ = calendar
date_time
|> Time.date_time_to_moment()
|> Lunar.illuminated_fraction_of_moon()
end
def illuminated_fraction_of_moon_at(unquote(Guards.date()) = date) do
_ = calendar
date
|> Date.to_gregorian_days()
|> Lunar.illuminated_fraction_of_moon()
end
@doc """
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]}
"""
@doc since: "0.5.0"
@spec date_time_new_moon_before(date()) ::
{:ok, Calendar.datetime()}, {:error, {module(), String.t}}
def date_time_new_moon_before(unquote(Guards.datetime()) = date_time) do
_ = calendar
date_time
|> Time.date_time_to_moment()
|> Lunar.date_time_new_moon_before()
|> Time.date_time_from_moment()
end
def date_time_new_moon_before(unquote(Guards.date()) = date) do
_ = calendar
date
|> Date.to_gregorian_days()
|> Lunar.date_time_new_moon_before()
|> Time.date_time_from_moment()
end
@doc """
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]}
"""
@doc since: "0.5.0"
@spec date_time_new_moon_at_or_after(date) ::
{:ok, Calendar.datetime()}, {:error, {module(), String.t}}
def date_time_new_moon_at_or_after(unquote(Guards.datetime()) = datetime) do
_ = calendar
datetime
|> Time.date_time_to_moment()
|> Lunar.date_time_new_moon_at_or_after()
|> Time.date_time_from_moment()
end
def date_time_new_moon_at_or_after(unquote(Guards.date()) = date) do
_ = calendar
date
|> Date.to_gregorian_days()
|> Lunar.date_time_new_moon_at_or_after()
|> Time.date_time_from_moment()
end
@doc """
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
"""
@doc since: "0.5.0"
@spec lunar_phase_at(date()) :: phase()
def lunar_phase_at(unquote(Guards.datetime()) = date_time) do
_ = calendar
date_time
|> Time.date_time_to_moment()
|> Lunar.lunar_phase_at()
end
def lunar_phase_at(unquote(Guards.date()) = date) do
_ = calendar
date
|> Date.to_gregorian_days()
|> Lunar.lunar_phase_at()
end
@doc """
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](https://unicode-table.com/en/sets/moon/).
### 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()
"🌕"
"""
@emoji_base 0x1f310
@emoji_phase_count 8
@emoji_phase (360.0 / @emoji_phase_count)
@spec lunar_phase_emoji(phase()) :: String.t()
def lunar_phase_emoji(360) do
lunar_phase_emoji(0)
end
def lunar_phase_emoji(phase) when is_lunar_phase(phase) do
offset = ceil(phase / @emoji_phase + 0.5)
:unicode.characters_to_binary([offset + @emoji_base])
end
@doc """
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]}
"""
@doc since: "0.5.0"
@spec date_time_lunar_phase_at_or_before(date(), Astro.phase()) ::
{:ok, Calendar.datetime()}, {:error, {module(), String.t}}
def date_time_lunar_phase_at_or_before(unquote(Guards.datetime()) = date_time, phase) do
_ = calendar
date_time
|> Time.date_time_to_moment()
|> Lunar.date_time_lunar_phase_at_or_before(phase)
|> Time.date_time_from_moment()
end
def date_time_lunar_phase_at_or_before(unquote(Guards.date()) = date, phase) do
_ = calendar
date
|> Date.to_gregorian_days()
|> Lunar.date_time_lunar_phase_at_or_before(phase)
|> Time.date_time_from_moment()
end
@doc """
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]}
"""
@doc since: "0.5.0"
@spec date_time_lunar_phase_at_or_after(date(), Astro.phase()) ::
{:ok, Calendar.datetime()}, {:error, {module(), String.t}}
def date_time_lunar_phase_at_or_after(unquote(Guards.datetime()) = date_time, phase) do
_ = calendar
date_time
|> Time.date_time_to_moment()
|> Lunar.date_time_lunar_phase_at_or_after(phase)
|> Time.date_time_from_moment()
end
def date_time_lunar_phase_at_or_after(unquote(Guards.date()) = date, phase) do
_ = calendar
date
|> Date.to_gregorian_days()
|> Lunar.date_time_lunar_phase_at_or_after(phase)
|> Time.date_time_from_moment()
end
@doc """
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 `t:Geo.Point.t/0` struct to represent a location without elevation
* a `t:Geo.PointZ.t/0` 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.
* `:astronomical` representing 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 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. `:utc` can be specified or 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 the configured Elixir time zone database or
one of `Tzdata.TimeZoneDatabase` or `Tz.TimeZoneDatabase`
depending upon which dependency is configured.
* `:time_zone_resolver` is a 1-arity function that resolves the
time zone name for a given location. The function will receive
a `%Geo.Point{cordinates: {lng, lat}}` struct and is expected to
return either `{:ok, time_zone_name}` or `{:error, :time_zone_not_found}`.
The default is `TzWorld.timezone_at/1` if `:tz_world` is
configured.
### Returns
* a `t:DateTime.t/0` representing the time of sunrise in the
requested timzone at the requested location.
* `{:error, :time_zone_not_found}` if the requested
time zone is unknown.
* `{:error, :time_zone_not_resolved}` if it is not possible
to resolve a time zone name from the location. This can happen
if `:tz_world` is not configured as a dependency and no
`:time_zone_resolver` option is specified.
* `{:error, :no_time}` if for the requested date
and location there is no sunrise. This can occur at
very high and very low latitudes during summer and winter.
### Notes
* If the resolved UTC date time is ambiguous because of a daylight savings
transition, the second of the two possibilities is applied. See
the `DateTime.from_naive/3` for more information.
### 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 sunrise(location, date, options) ::
{:ok, DateTime.t()} | {:error, :time_zone_not_found | :time_zone_not_resolved | :no_time}
def sunrise(location, date, options \\ default_options()) when is_list(options) do
options = Keyword.put(options, :rise_or_set, :rise)
Solar.sun_rise_or_set(location, date, options)
end
@doc """
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.
* `:astronomical`representing 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 in which the sunset
is requested. The default is `:default` in which
the sunrise time is reported in the time zone of
the requested location. `:utc` can be specified or 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 the configured Elixir time zone database or
one of `Tzdata.TimeZoneDatabase` or `Tz.TimeZoneDatabase`
depending upon which dependency is configured.
* `:time_zone_resolver` is a 1-arity function that resolves the
time zone name for a given location. The function will receive
a `%Geo.Point{cordinates: {lng, lat}}` struct and is expected to
return either `{:ok, time_zone_name}` or `{:error, :time_zone_not_found}`.
The default is `TzWorld.timezone_at/1` if `:tz_world` is
configured.
### Returns
* a `t:DateTime.t/0` representing the time of sunset in the
requested time zone at the requested location.
* `{:error, :time_zone_not_found}` if the requested
time zone is unknown.
* `{:error, :time_zone_not_resolved}` if it is not possible
to resolve a time zone name from the location. This can happen
if `:tz_world` is not configured as a dependency and no
`:time_zone_resolver` option is specified.
* `{:error, :no_time}` if for the requested date
and location there is no sunset. This can occur at
very high and very low latitudes during summer and winter.
### Notes
* If the resolved UTC date time is ambiguous because of a daylight savings
transition, the second of the two possibilities is applied. See
the `DateTime.from_naive/3` for more information.
### 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}
"""
@spec sunset(location, date, options) ::
{:ok, DateTime.t()} | {:error, :time_zone_not_found | :time_zone_not_resolved | :no_time}
def sunset(location, date, options \\ default_options()) when is_list(options) do
options = Keyword.put(options, :rise_or_set, :set)
Solar.sun_rise_or_set(location, date, options)
end
@doc """
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 equinox(Calendar.year(), :march | :september) :: {:ok, DateTime.t()}
def equinox(year, event) when event in [:march, :september] and year in 1000..3000 do
Solar.equinox_and_solstice(year, event)
end
@doc """
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 solstice(Calendar.year(), :june | :december) :: {:ok, DateTime.t()}
def solstice(year, event) when event in [:june, :december] and year in 1000..3000 do
Solar.equinox_and_solstice(year, event)
end
@doc """
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 solar_noon(Astro.location(), Calendar.date()) :: {:ok, DateTime.t()}
def solar_noon(location, date) do
%Geo.PointZ{coordinates: {longitude, _, _}} = Location.normalize_location(location)
julian_day = Time.julian_day_from_date(date)
julian_centuries = Time.julian_centuries_from_julian_day(julian_day)
julian_centuries
|> Solar.solar_noon_utc(-longitude)
|> Time.datetime_from_date_and_minutes(date)
end
@doc """
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_apparent_longitude(Calendar.date()) :: degrees()
def sun_apparent_longitude(date) do
date
|> Time.julian_day_from_date()
|> Time.julian_centuries_from_julian_day()
|> Solar.sun_apparent_longitude()
end
@doc """
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 hours_of_daylight(Astro.location(), Calendar.date()) :: {:ok, Elixir.Time.t()}
def hours_of_daylight(location, date) do
with {:ok, sunrise} <- sunrise(location, date),
{:ok, sunset} <- sunset(location, date) do
seconds_of_sunlight = DateTime.diff(sunset, sunrise)
{hours, minutes, seconds} = Time.seconds_to_hms(seconds_of_sunlight)
Elixir.Time.new(hours, minutes, seconds)
else
{:error, :no_time} ->
if no_daylight_hours?(location, date) do
Elixir.Time.new(0, 0, 0)
else
Elixir.Time.new(23, 59, 59)
end
end
end
@polar_circle_latitude 66.5631
defp no_daylight_hours?(location, date) do
%Geo.PointZ{coordinates: {_longitude, latitude, _elevation}} =
Location.normalize_location(location)
cond do
(latitude >= @polar_circle_latitude and date.month in 10..12) or date.month in 1..3 -> true
latitude <= -@polar_circle_latitude and date.month in 4..9 -> true
true -> false
end
end
@doc false
# beta and lambda in degrees
@spec declination(Time.moment(), Astro.angle(), Astro.angle()) :: Astro.angle()
def declination(t, beta, lambda) do
julian_centuries = Time.julian_centuries_from_moment(t)
epsilon = obliquity_correction(julian_centuries)
:math.asin(sin(beta) * cos(epsilon) + cos(beta) * sin(epsilon) * sin(lambda))
|> Math.to_degrees
|> mod(360.0)
end
@doc false
# beta and lambda in degrees
@spec right_ascension(Time.moment(), Astro.angle(), Astro.angle()) :: Astro.angle()
def right_ascension(t, beta, lambda) do
julian_centuries = Time.julian_centuries_from_moment(t)
epsilon = obliquity_correction(julian_centuries)
# omega = (125.04 - (1_934.136 * julian_centuries))
# adjusted_epsilon = (epsilon + 0.00256 * cos(omega))
atan_r(sin(lambda) * cos(epsilon) - tan(beta) * sin(epsilon), cos(lambda))
|> Math.to_degrees()
end
@doc false
def default_options do
default_time_zone_db =
cond do
Application.get_env(:elixir, :time_zone_database) -> Application.get_env(:elixir, :time_zone_database)
Code.ensure_loaded?(Tzdata.TimeZoneDatabase) -> Tzdata.TimeZoneDatabase
Code.ensure_loaded?(Tz.TimeZoneDatabase) -> Tz.TimeZoneDatabase
end
[
solar_elevation: Solar.solar_elevation(:geometric),
time_zone: :default,
time_zone_database: default_time_zone_db
]
end
end
