# Sight Reduction

This page allows you to compute sight reductions. The inputs are entered into the gray entry areas in rows 1 to 3. The E or W suffix after LHA is set depending whether the body is East or West of the observer. If W, Zn = 360 - Z else Zn = Z for a north elevated pole. (For South Lats, someone please check Z and Zn calculations.) Try

1. LHA 8 ° 18.1 ´ E,
2. Lat 39 ° 50.6 ´ N,
3. Dec 23 ° 8.4 ´ N,

which gives Hc = 71 ° 52.8 ´    Zn = 154 ° 43.7 ´ which rounds to 155 °.

The answer for Hc is in 5. The first degree column contains the decimal degrees while the next two columns give the answer in degrees and minutes.

Zn is in 8. Note that 8 is generally rounded to the nearest degree. Row 7. Contains Z and the decimal value in the first column may be useful.

 1 Enter the Hour Angle of the body (LHA or t) ° ´ E W = ° 2 Enter your Latitude (L) ° ´ N S = ° 3 Enter the Declination of the body (D) ° ´ N S = °
4. Zenith Distance (z) ° =  ° ´
5. Calculated Altitude Hc ( = 90-z ) ° =  ° ´
6. P Polar Distance (co-D) of body ° =  ° ´
7. Z azimuth (interior) angle of body ° =  ° ´
8. Zn azimuth angle of body (from true north) ° =  ° ´