# Astro

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Astro is a library to provide basic astromonomical functions with a focus on functions that support solar, lunar and lunisolar calendars such as the Chinese, Hebrew and Persian calendars.

## Usage

The two primary functions are `Astro.sunrise/3` and `Astro.sunset/3`.

### Examples
# Sunrise in Sydney on December 4th
iex> Astro.sunrise({151.20666584, -33.8559799094}, ~D[2019-12-04])
{:ok, #DateTime<2019-12-04 05:37:00.000000+11:00 AEDT Australia/Sydney>}

# Sunset in Sydney on December 4th
iex> 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 the town of Alert in Nunavut, Canada
# ...doesn't exist since there is no sunset in summer
iex> Astro.sunset({-62.3481, 82.5018}, ~D[2019-07-01])
{:error, :no_time}

# ...or sunrise in winter
iex> Astro.sunrise({-62.3481, 82.5018}, ~D[2019-12-04])
{:error, :no_time}
### Specifying a location
The desired location of sunrise or sunset can be specified as either:

* a tuple of longitude and latitude (note the order) such as `{-62.3481, 82.5018}`
* a tuple of longitude, latitude and elevation (note the order) such as `{-62.3481, 82.5018, 0}`. The elevation is specified in meters.
* a `Geo.Point.t` struct
* a `Geo.PointZ.t` struct

## Status

Sunrise and sunset calculations are tested to be within 1 minute of

## Solar functions

* [X] Sunrise
* [X] Sunset
* [X] Solstice
* [X] Equinox

## Lunar functions

* [ ] Moon phase
* [ ] Moon rise
* [ ] Moon set

## References

* Thanks to @pinnymz for the [ruby-zmanim]( gem which has a well structured ruby implementation of sunrise / sunset and some core astronomical algorithms.

* Eventually all roads lead to the canonical book on the subject by Jean Meeus: [Astronomical Algorithms](

* For the intersection of calendars and astronomy, [Calendrical Calculations]( by Nachum Dershowitz and Edward M. Reingold remains the standard reference.

* On the web, []( is a great reference. The sunrise/sunset calculations in this library are tested to return times within 1 minute of results.

* [Wikipedia]( for content to help describe the understanding behind some of the functions

## Installation

Astro can be installed by adding `astro` to your list of dependencies in `mix.exs`:

def deps do
    {:astro, "~> 0.1.0"}
Then get dependencies and install the data required to determine a time zone from a location which is used by the dependency `tz_world`.

mix deps.get
mix tz_world.update

Documentation can be found at [](