sextant altitude to apparent altitude

Calculation: sextant altitude Hs to apparent altitude Ha to correct the sextant’s inherent errors and the error induced by the height of the eye (Dip) above the horizon. (Altitude = Height)

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.

sextant altitude to apparent altitude, sextant inherent errors and due to height of the eye above the sea level

Lake Michigan at Newport State Park, Door County, Wisconsin. Unknown author

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.

sextant altitude to apparent altitude: On this page

Calculating Hs to Ha:

(The Dip error is always negative !)


Hambantota District in southern Sri Lanka. Author image: Sara Weerarathne

sextant altitude to apparent altitude:

Example: How to calculate apparent height (Ha)

The entries:

sextant altitude

sextant altitude to apparent altitude lecture sextant altitude image
sextant altitude (Hs) = 74°06′

Hs = 74° 06′


Index error

sextant altitude to apparent altitude: image sextant index error
error = +7′

Index error = + 0° 07′


Non adjustable error

sextant altitude to apparent altitude image inspection certificate

Hs = 74°06 is about 75° so the error is +1′

Non adjustable error = + 0° 01′


non adjustable error + index error = + 8′


eye height (Dip error)

sextant altitude to apparent altitude image eye height
eye height = 2 m

DIP = – 0°02′,5 = – 2′,5 (eye height = 2 meters)

DIP of the horizon: see altitude correction table

ALTITUDE CORRECTION TABLE:

sextant altitude to apparent altitude image correction table
apparent altitude and DIP correction table (FOR SUN ONLY) nautical almanac style

sextant altitude to apparent altitude: solution of the example

sextant height (Hs) to apparent height (Ha)

Hs …………………..= 74° 06′, 0

index error……… = 00° 08′, 0 (index + non adj. error)

Dip………………… = – 00° 02′, 5

 _________________________ +

Ha…………………. = 74° 11′, 5

sun correct LL ….= _ _° _ _’, _ 

__________________________ +

Ho…………………….= _ _° _ _’, _

 the Boukana beach of the Nador region in Morocco. Author image: Sapha Bouamara