On this page, a practical calculation is shown from the sextant altitude (Hs) to the apparent altitude (Ha), taking into account the sextant’s inherent errors and the error caused by the observer’s eye height (Dip) above the horizon.
This page contributes to the primary objective of offering guidance and interactivity on the calculation and understanding of the Line of Position (LOP) using only a sextant and the sun, and then tracing this line on a plotting sheet. See recommendations.
On this page, we will learn how to calculate the apparent height of the sun. However, I recommend first reading the theory of apparent sextant height.
Calculating Hs to Ha:
(The Dip error is always negative !)
sextant altitude to apparent altitude: example
How to calculate apparent height (Ha)
The entries:
sextant altitude
Hs = 74° 06′
Index error
Index error = + 0° 07′
Non-adjustable error
Hs = 74°06 is about 75° so the error is +1′
Non-adjustable error = + 0° 01′
ε = non-adjustable error + index error = + 8′
eye height (Dip error)
DIP = – 0°02′.5 = – 2′.5 (eye height = 2 meters)
DIP of the horizon: see altitude correction table
ALTITUDE CORRECTION TABLE:
All the data above has been calculated by the author and owner of www.easysextant.com / ladroitedehauteur.com.
Tables for eye height up to 12 meters and measurement of the Sun’s lower limb only.
sextant altitude to apparent altitude: solution of the example
sextant height (Hs) to apparent height (Ha)
Hs …………………..= 74° 06′, 0
ε ………………….. = + 00° 08′, 0
Dip………………… = – 00° 02′, 5
_________________________ +
Ha…………………. = 74° 11′, 5
