# Astro
[](https://hex.pm/packages/astro)
[](https://hex.pm/packages/astro)
[](https://hex.pm/packages/astro)
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
```elixir
# 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{}` struct
* a `Geo.PointZ{}` struct
## Status
Sunrise and sunset calculations are tested to be within 1 minute of
## Solar functions
* [X] Sunrise
* [X] Sunset
* [ ] Solstice
* [ ] Equinox
## Lunar functions
* [ ] Moon phase
* [ ] Moon rise
* [ ] Moon set
## References
* Thanks to @pinnymz for the [ruby-zmanim](https://github.com/pinnymz/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](https://www.amazon.com/Astronomical-Algorithms-Jean-Meeus/dp/0943396352)
* For the intersection of calendars and astronomy, [Calendrical Calculations](https://www.amazon.com/Calendrical-Calculations-Ultimate-Edward-Reingold/dp/1107683165) by Nachum Dershowitz and Edward M. Reingold remains the standard reference.
* On the web, [timeanddate.com](https://www.timeanddate.com/astronomy/) is a great reference. The sunrise/sunset calculations in this library are tested to return times within 1 minute of timeanddate.com results.
## Installation
Astro can be installed by adding `astro` to your list of dependencies in `mix.exs`:
```elixir
def deps do
[
{:astro, "~> 0.1.0"}
]
end
```
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 [https://hexdocs.pm/astro](https://hexdocs.pm/astro).
