README.md

AstroPC

Library of core routines for practical astronomy.

• AstroPC
  • Features
  • Getting started
  • Usage
    • Running examples
  • Unit tests
  • Additional information
    • Civil vs. Astronomical year
    • Zero day
    • Gregorian calendar
  • Sources
  • How to contribute
  • Footnotes

Features

• Converts between Civil and Julian dates.
• Calculates difference between Universial Coordinated and Terrestrial Dynamic time (Delta-T).
• Calculates Sidereal (Stellar) time.
• Calculates Nutation and Obliquity of the ecliptic.
• Transforming between various types of celestial coordinates.
• Miscallenous mathematical routines usefull for practical astronomy.
• Accurate positions of Sun, Moon and the planets, including Pluto.
• Time of solstices, equinoxes and lunations.

Getting started

Add to pubspec.yaml of your project

dependencies:
  ...
  astropc:
    git:
      url: https://github.com/ilbagatto/astropc.git
      ref: master
  ...

Then run:

$ dart pub update

Usage

See tests/ and examples/ for usage examples.

Running examples

$ dart .\example\julian.dart 
$ dart .\example\julian.dart --help

You may also compile the examples to platform-specific binary, e.g.:

> dart compile exe .\example\julian.dart
> example\julian.exe

Unit tests

$ dart test ./test

Additional information

Civil vs. Astronomical year

There is disagreement between astronomers and historians about how to count the years preceding the year 1. Astronomers generally use zero-based system. The year before the year +1, is the year zero, and the year preceding the latter is the year -1. The year which the historians call 585 B.C. is actually the year -584.

Zero day

Zero day is a special case of date: it indicates 12h UT of previous calendar date. For instance, 1900 January 0.5 is often used instead of 1899 December 31.5 to designate start of the astronomical epoch.

Gregorian calendar

Civil calendar in most cases means proleptic Gregorian calendar. it is assumed that Gregorian calendar started at Oct. 4, 1582, when it was first adopted in several European countries. Many other countries still used the older Julian calendar. In Soviet Russia, for instance, Gregorian system was accepted on Jan 26, 1918. See Wiki article.

Sources

The formulae were adopted from the following sources:

• Peter Duffett-Smith, "Astronomy With Your Personal Computer", Cambridge University Press, 1997
• Jean Meeus, "Astronomical Algorithms", 2d edition, Willmann-Bell, 1998
• J.L.Lawrence, "Celestial Calculations", The MIT Press, 2018

How to contribute

You may contribute to the project by many different ways, starting from refining and correcting its documentation, especially if you are a native English speaker, and ending with improving the code base. Any kind of testing and suggestions are welcome.

You may follow the standard Github procedures or, in case you are not comfortable with them, just send your suggestions to the author by other means.

Footnotes