Please say hi to a new lib, Astro that aims to deliver easy-to-consume astronomy calculations of practical use. For now it only calculates sunrise and sunset. In testing its precision is within 1 minute of the results returns from DateAndTime.com.
It makes use of tz_world to dereference geo coordinates to a timezone and tzdata for time zone conversions.
This lib started our as a requirement to support certain solar, lunar and lunisolar calendars but it has wider applicability.
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}
Seconds are no longer truncated to zero when calculating datetimes and durations
Enhancements
Add Astro.solar_noon/2 to return the true solar noon for a location and date
Add Astro.hours_of_daylight/2 to return hours, minutes and seconds as a Time.t() representing the number of daylight hours for a give location and date
Add Astro.sun_apparent_longitude/1 to return the apparent solar longitude on a given date. The result, a number of degrees between 0 and 360, can be used to determine the seasons.
This completes the work required to support the Persian calendar which will be landing on hex.pm in the next couple of days.
Astro version 0.5.0 is now out. The release adds functions that calculate the phase of the moon which, apart from anything else, is needed to calculate the Chinese calendar. Please note that Elixir 1.11 or later is required.
Bug Fixes
Updates documentation to be clear about installation and setup requirements for tz_world
Fixes test data for São Paulo now that it no longer uses DST
Ensure :astro is started in test mode
Enhancements
This primary focus of this release is to add lunar calculations for moon phase.
Astro version 0.6.0 is now out. This version avoids requiring some dependencies which makes the footprint smaller and compilation much faster. I have been using it to support the upcoming Chinese calendar with all tests passing so I consider the basic solar and lunar algorithms to be in solid shape.
Please note that Elixir 1.11 or later is required.
Roadmap
Roadmap to version 1.0 is to add Astro.moonrise/2 and Astro.moonset/2.
Additional development proposals or suggestions are very welcome.
Bug Fixes
Fix Astro.Math.atan_r/2
Fix Astro.Earth.ephemeris/1
Breaking changes
Change Astro.Time.date_time_{from, to}_iso_days/1 to Astro.Time.date_time_{from, to}_moment/1
Enhancements
Remove dependency on ex_cldr_calendar and jason
Add Astro.sun_position_at/1 which is a public API for returning the right ascension, declination and radius (distance to the sun) at a given date/time.
Add Astro.moon_position_at/1 which is a public API for returning the right ascension, declination and radius (distance to the moon) at a given date/time.
Add Astro.illuminated_fraction_of_moon_at/1 to return the fraction of the moon that is lit at a given date/time.
I’ve released Astro 1.0 almost exactly a year after the last published version. This indicates API stability for existing functions (stable in most cases for at least 3 years). There is only one new function in this release:
Enhancements
Release 1.0. This library was started four years ago and the public API has been stable for at least three of those years.
Adds Astro.sun_azimuth_altitude/2. Thanks to @kimlai for the suggestion. Closes #3.
I’ve published Astro version 1.0.2. The primary fix is to calculate astronomical, nautical and civil sunrise/sunset correctly. The changelog entry is:
Bug Fixes
Fix sunrise/sunset calculations when the solar elevation isn’t 90 degrees. Thanks to @cloud8421 for the issue. Closes #5.
Elixir 1.17 support
Astro compiles and runs without warnings on Elixir 1.17.
The difference between dawn and sunrise
There are four main daily milestones in the progress from darkness to light each day.
Astronomical twilight is calculated when the geometric centre of the sun is 18 degrees below the horizon. This is the solar elevation where stars start to disappear agains the sky’s background. Therefore typically the time at which optical observation will stop.
Nautical twilight is calculated when the geometric centre of the sun is 12 degrees below the horizon. This is the time at which the horizon can be observed by eye although it is not generally considered light enough for outdoor activity. The important of seeing the horizon is understandable for mariners.
Civil twilight is what is generally considered to be dawn and is calculated when the geometric centre of the sun is 6 degrees below the horizon. This is the point at which outdoor activity is possible due to light from the sun below the horizon refracting in the atmosphere.
Sunrise is calculated when the upper edge of the sun breaks the horizon, adapted to account for refraction of the suns rays.
Each of these - and indeed any arbitrary solar elevation - can be calculated in Astro by:
I’ve just published Astro 1.1.0 with the following changelog entry. Please note the breaking change to configuration (there are no breaking changes to application code).
Breaking Change
:tz_world is no longer a required dependency - it is now an optional dependency. This library is used to resolve a time zone name from a given latitude and longitude. When configured, it becomes the default method of resolving time zone names from a location. However it is no possible to provide alternative implementations for this resolution using the :time_zone_resolver option.
To retain the previous behaviour, applications should add {:tz_world, "~> 1.0"} to their dependencies.
Enhancements
Adds an option :time_zone_resolver to Astro.sunrise/3 and Astro.sunset/3 that is a 1-arity function that is invoked to resolve the time zone name from a given latitude and longitude. The default is to use TzWorld.timezone_at/1 if TzWorld is configured, otherwise an error is returned.
The default time zone database is now detected in the following order:
Application.get_env(:elixir, :time_zone_database)
TzData.TimeZoneDatabase if TzData is configured
Tz.TimeZoneDatabase if Tz is configured
Thanks to @cloud8421 for the motivation and encouragement to get this done.
Is it possible to use it with 
