Identify a heavenly body whose azimuth you want to take. Ensure that the altitude is not too high or too low (preferably between 20o and 60o Take the compass bearing of the body and at the same time note the corrected GMT, and your DR (dead reckoning) position
Procedure for calculating actual azimuth (ABC tables/ calculator)
Use of ABC tables Obtain the declination of the body and the LHA (local hour angle) of the body at that time from the nautical almanac. With LHA and DR latitude as arguments, obtain value of “A” from ABC tables. ‘A’ is named opposite to latitude, except when hour angle is between 90 degrees and 270 degrees. With LHA and declination as arguments, obtain value of “B”. ‘B’ is always named same as declination. Calculate “C” which is the algebraic sum of “A” and “B”.
If ‘A’ and ‘B’ are same names then add and retain the name
If ‘A’ and ‘B’ are contrary names then subtract and retain name of the larger one Now enter table “C” with DR latitude and value of “C” obtained as above to get the azimuth. Naming of azimuth is as follows:
The prefix ‘N’ or ‘S’ of value ‘C’ above is retained.
For finding the suffix whether ‘E’ or ‘W’ – If LHA is between 000o & 180o, the body lies to the West and if it is between 180o and 360o the body lies to the East.
The method of naming (N or S, E or W) and signs (+ve or -ve) of the values of ‘A’, ‘B’ & ‘C’ obtained from the ABC tables are given in the tables itself.
Use of calculator
A = Tan Lat/ Tan P
B = Tan dec / Sin P
Tan Az = 1 / C x Cos Lat
Rules for naming A, B, C and Azimuth are as explained above (given in the nautical tables)
If LHA between 000o and 180o, P = LHA
If LHA between 180o and 360o, P = 360 – LHA
If LHA is 360o or 180o then azimuth will be 000o or 180o (Body on the observer’s meridian or inferior meridian)
