practical-astronomy-c

Algorithms from "Practical Astronomy with your Calculator or Spreadsheet" by Peter Duffett-Smith, implemented in C.

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

Library Functions - Status

Date/Time

• Calculate -> Date of Easter
• Convert -> Civil Date to Day Number
• 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

• 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
• Calculate -> RA and Declination values, corrected for geocentric parallax
• Calculate -> Heliographic coordinates
• Calculate -> Carrington rotation number
• Calculate -> Selenographic (lunar) coordinates (sub-Earth and sub-Solar)

The Sun

• 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

• Calculate -> Approximate position of planet
• Calculate -> Precise position of planet
• Calculate -> Visual aspects of planet (distance, angular diameter, phase, light time, position angle of bright limb, and apparent magnitude)

Comets

• Calculate -> Position of elliptical comet
• Calculate -> Position of parabolic comet

Binary Stars

• Calculate -> Binary star orbit data

The Moon

• Calculate -> Approximate position of Moon
• Calculate -> 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

• Calculate -> Lunar eclipse occurrence and circumstances
• Calculate -> Solar eclipse occurrence and circumstances