Astronoby

Ruby library that provides a useful API for computing astronomical calculations.

Some algorithms are based on the following astrometry books:

• Astronomical Algorithms by Jean Meeus
• Celestial Calculations by J. L. Lawrence
• Practical Astronomy with your Calculator or Spreadsheet by Peter Duffet-Smith and Jonathan Zwart

Solar System bodies' positions are computed based on ephemerides from the IMCCE or NASA/JPL.

Content

• Installation
• Usage Documentation
• Precision
• Development
• Contributing
• License
• Code of Conduct

Installation

Install the gem and add to the application's Gemfile by executing:

$ bundle add astronoby

If Bundler is not being used to manage dependencies, install the gem by executing:

$ gem install astronoby

Usage Documentation

Since version 0.7.0, the usage documentation resides in docs/. For previous versions, you can access the documentation in the README for each release.

See also

• Quick Start Guide - for getting started examples
• Celestial Bodies - for understanding planets and objects
• Reference Frames - for coordinate systems
• Observer Setup - for location configuration
• Glossary - for astronomical and technical terms

Expected breaking changes notice

This library is still in heavy development. The public API is not stable, so please be aware that new minor versions will probably lead to breaking changes until a major one is released.

Changes are documented in the CHANGELOG and adapting to breaking changes is described in the UPGRADING document.

Precision

The current precision for the major Solar System bodies' locations in the sky as seen from an observer on Earth is below 10 arc seconds. This corresponds to half the size of Saturn when it is closest to Earth.

While the precision is not enough for spacecraft navigation, it is enough for automated guiding of amateur telescopes.

The sources used for comparison are: IMCCE, JPL Horizons, Stellarium, and the Skyfield library.

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and the created tag, and push the .gem file to rubygems.org.

Performance

The library is designed to be fast, but there is always room for improvement. When comparing the performance of two implementations, please use the performance benchmark in the console before and after your implementation.

$ bin/console

require_relative "benchmarks/performance"

PerformanceBenchmark.new.run

For fast feedback, you can customise the parameters:

PerformanceBenchmark
  .new(warmup_runs: 1, measure_runs: 3, iterations_per_run: 5)
  .run

Performance is not absolute, which is why the results are not documented here. What is important is to compare the relative performance of two implementations and make sure new features do not degrade performance.

Contributing

Please see CONTRIBUTING.md.

License

The gem is available as open source under the terms of the MIT License.

Code of Conduct

Everyone interacting in the Astronoby project's codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.