practical-astronomy 0.0.2

Algorithms from Practical Astronomy, implemented in Python

practical-astronomy-python

Algorithms from "Practical Astronomy with your Calculator or Spreadsheet" by Peter Duffett-Smith, implemented in Python 3. API documentation is published here.

If you're interested in this topic, please buy the book! It provides far more detail and context.

CLI

Work is started on a command-line interface, but only the date/time functions are implemented, so far. Results are formatted as JSON.

Invoke as ./pa-cli.py -h to see all of the options:

$ ./pa-cli.py -h

usage: pa-cli.py [-h] [--cd CD] [--ct CT] [--dh DH] [--gd GD] [--gl GL] [--gst GST] [--lst LST] [--jd JD] [--ut UT] [--year YEAR] [--dst] [--st] [--zc ZC] [--doe] [--cd_to_dn] [--gd_to_jd] [--jd_to_gd] [--ct_to_dh] [--dh_to_ct] [--lct_to_ut] [--ut_to_lct] [--ut_to_gst] [--gst_to_ut] [--gst_to_lst] [--lst_to_gst]

Practical Astronomy CLI.

optional arguments:
  -h, --help    show this help message and exit

Actions:
  --doe         Calculate date of Easter, for a given year.
  --cd_to_dn    Convert civil date to day number.
  --gd_to_jd    Convert Greenwich date to Julian date.
  --jd_to_gd    Convert Julian date to Greenwich date.
  --ct_to_dh    Convert civil time to decimal hours.
  --dh_to_ct    Convert decimal hours to civil time.
  --lct_to_ut   Convert local civil time to universal time.
  --ut_to_lct   Convert universal time to local civil time.
  --ut_to_gst   Convert universal time to Greenwich sidereal time.
  --gst_to_ut   Convert Greenwich sidereal time to universal time.
  --gst_to_lst  Convert Greenwich sidereal time to local sidereal time.
  --lst_to_gst  Convert local sidereal time to Greenwich sidereal time.

Inputs (used by Actions):
  --cd CD       Civil date. Input format: 'mm/dd/yyyy'
  --ct CT       Civil time. Input format: 'hh:mm:ss'
  --dh DH       Decimal hours. Input format: floating point number, e.g., 18.52416667
  --gd GD       Greenwich date. Input format: 'mm/dd/yyyy'. Fractional day is allowed, e.g., '6/19.75/2009'
  --gl GL       Geographical longitude. Input format: (+/-)##.##, e.g., -64.00
  --gst GST     Greenwich sidereal time. Input format: 'hh:mm:ss'
  --lst LST     Local sidereal time. Input format: 'hh:mm:ss'
  --jd JD       Julian date. Input format: floating point number, e.g., 2455002.25
  --ut UT       Universal time. Input format: 'hh:mm:ss'
  --year YEAR   Calendar year, e.g. 2019.

Inputs (time zone management):
  --dst         Observe daylight savings time.
  --st          Observe standard time (default)
  --zc ZC       Offset, in hours, for time zone correction.

Example

Convert universal time to Greenwich sidereal time:

$./pa-cli.py --ut_to_gst --ut "14:36:51.67" --gd "4/22/1980"

{"greenwichSiderealTimeHours": 4, "greenwichSiderealTimeMinutes": 40, "greenwichSiderealTimeSeconds": 5.23}

Unit Tests

Unit test run can be invoked via the Make utility:

make all

Library Functions

Date/Time

Type	Description
Calculate	Date of Easter
Convert	Civil Date to Day Number
Convert	Greenwich Date <-> Julian Date
Convert	Julian Date to Day-of-Week
Extract	Day, Month, and Year parts of Julian Date
Convert	Civil Time <-> Decimal Hours
Extract	Hour, Minutes, and Seconds parts of Decimal Hours
Convert	Local Civil Time <-> Universal Time
Convert	Universal Time <-> Greenwich Sidereal Time
Convert	Greenwich Sidereal Time <-> Local Sidereal Time

Coordinates

Type	Description
Convert	Angle <-> Decimal Degrees
Convert	Right Ascension <-> Hour Angle
Convert	Equatorial Coordinates <-> Horizon Coordinates
Calculate	Obliquity of the Ecliptic
Convert	Ecliptic Coordinates <-> Equatorial Coordinates
Convert	Equatorial Coordinates <-> Galactic Coordinates
Calculate	Angle between two objects
Calculate	Rising and Setting times for an object
Calculate	Precession (corrected coordinates between two epochs)
Calculate	Nutation (in ecliptic longitude and obliquity) for a Greenwich date
Calculate	Effects of aberration for ecliptic coordinates
Calculate	RA and Declination values, corrected for atmospheric refraction and geocentric parallax
Calculate	Heliographic coordinates
Calculate	Carrington rotation number
Calculate	Selenographic (lunar) coordinates (sub-Earth and sub-Solar)

The Sun

Type	Description
Calculate	Approximate and precise positions of the Sun
Calculate	Sun's distance and angular size
Calculate	Local sunrise and sunset
Calculate	Morning and evening twilight
Calculate	Equation of time
Calculate	Solar elongation

Planets

Type	Description
Calculate	Approximate and precise position of planet
Calculate	Visual aspects of planet (distance, angular diameter, phase, light time, position angle of bright limb, and apparent magnitude)
Calculate	Position of comet (elliptical and parabolic)
Calculate	Binary star orbit data

The Moon

Type	Description
Calculate	Approximate and precise position of Moon
Calculate	Moon phase and position angle of bright limb
Calculate	Times of new Moon and full Moon
Calculate	Moon's distance, angular diameter, and horizontal parallax
Calculate	Local moonrise and moonset

Eclipses

Type	Description
Calculate	Lunar eclipse occurrence and circumstances
Calculate	Solar eclipse occurrence and circumstances