Category:Astronomy

Books

• Practical Astronomy With Your Calculator by Peter Duffett-Smith, Third Edition, Cambridge University Press, 1988. ISBN 0-5213-5699-7
• Astronomical Formulae for Calculators by Jean Meeus, Third Edition, Willmann-Bell, 1985. ISBN 0-9433-9609-3
• Planetary Programs and Tables from -4000 to +2800 by Pierre Bretagnon and Jean-Louis Simon, Willmann-Bell, 1986.
• Celestial BASIC: Astronomy on Your Computer by Eric Burgess, Revised Edition, Sybex, 1985. ISBN 0-8958-8087-3

Programs, algorithms, and code

• Astro::Sunrise
• Astro::MoonPhase
• Astro::Coord
• Geo::Distance

Equations

Geo::Distance

Note: The d at the end of each of the following equations means "distance".

• hsin: Haversine Formula

 dlon = lon2 - lon1
 dlat = lat2 - lat1
 a = (sin(dlat/2))^2 + cos(lat1) * cos(lat2) * (sin(dlon/2))^2
 c = 2 * atan2( sqrt(a), sqrt(1-a) )
 d = R * c

Note: The hsin formula has improved accuracy over the cos formula.

• polar: Polar Coordinate Flat-Earth Formula

 a = pi/2 - lat1
 b = pi/2 - lat2
 c = sqrt( a^2 + b^2 - 2 * a * b * cos(lon2 - lon1) )
 d = R * c 

• cos: Law of Cosines for Spherical Trigonometry

 a = sin(lat1) * sin(lat2)
 b = cos(lat1) * cos(lat2) * cos(lon2 - lon1)
 c = arccos(a + b)
 d = R * c

Note: Although this formula is mathematically exact, it is unreliable for small distances because the inverse cosine is ill-conditioned.

• gcd: Great Circle Distance.

 c = 2 * asin( sqrt(
   ( sin(( lat1 - lat2 )/2) )^2 + 
   cos( lat1 ) * cos( lat2 ) * 
   ( sin(( lon1 - lon2 )/2) )^2
 ) )

• mt: Math::Trig great_circle_distance

 lat0 = 90 degrees - phi0
 lat1 = 90 degrees - phi1
 d = R * arccos(cos(lat0) * cos(lat1) * cos(lon1 - lon01) + sin(lat0) * sin(lat1))

External links

• Wiki Sky