Conversion from Celestial Coordinate to Horizon Coordinates

Quantities Needed:

• a = Right Ascension of the celestial object
• d = Declination of the celestial object
• f = Latitude of the observer
• L = Longitude of the observer (positive east, negative west)
• Date: Y = year, M = month of the year, D = day of the month
• Time: UT = Universal Time
  UT = Local Standard Time - Local Time Zone
  (negative west, positive east of Greenwich)
• JD = Julian Day
  

  A = int(Y/100) B = 2 - A + int(A/4) JD = int(365.25 (Y + 4716)) + int(30.6001 (M + 1) + D + B - 1524.5

• q_o = Siderial Time at Greenwich for the UT
  

  T = (JD + UT/24 - 2,451,545.0)/36525 qo = 280.46061837 + 360.985647366 29 ( JD -2,451,545.0) + 0.000387933 T2 - T3/38,710,000

• q = Local Siderial Time
  q = q_o + L
• H = Local hour angle
  H = q - a
  eg.
• A = Azimuth of the celestial object, measured westward from the south
  Note: This is different from the standard definition of the term which is measured eastward from the north
• h = altitude of the celestial object, positive above the horizon

• Time and Date --> Siderial Time at Greenwich
• Longitude, Siderial Time at Greenwich and Right ascension --> Local Hour Angle, H
• Latitude, Declination, and Local Hour Angle --> Azimuth, A and Altitude, h

• Date
• Time
• Latitude
• Longitude
• Right Ascension
• Declination

1. Obviously if you change the celestial object, the a and d change
2. If you move the observatory, Latitude and Longitude change
3. The time is changing continuously