Calculation: The conversion from sextant apparent altitude (Ha) to observed altitude (Ho) requires correction for atmospheric refraction and compensation for the varying diameters and distances of both the Sun and the Earth throughout the year.
Moreover, these adjustments collectively result in the final observed height, measured from the center of the Earth to the center of the Sun. (Altitude = Height)
Firstly, we examine the method for calculating the observed height of the sun.
Also, if you’ve been following the course, you’re already familiar with the underlying principles of observed height theory.
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 apparent to observed altitude: example calculation apparent altitude to observed altitude (Ha to Ho)
sextant apparent to observed altitude:
Three entries:
1)Ha = 32°14′,5 (Apparent altitude.)
In fact, this apparent height was obtained in the blue section (Hs to Ha)
2) Date: Observation somewhere in JULY
3) lower limb of the sun
Altitude correction table from The nautical almanac
The star and planet corrections, as well as the lower limb correction, appear on this page in the Nautical Almanac.
In fact, App altitude is about 32°, the observation between april and september and we took the lower limb → correction = 14′,5
Sextant apparent to observed altitude: solution example
Hs …………………. = _ _° _ _’, _
index error…….. = _ _° _ _’, _
Dip………………… = _ _° _ _’, _
_________________________ +
Ha………………….. = 32° 14′, 5
sun correct LL …= 00° 14′, 5
__________________________ +
Ho…………………….= 32° 29′, 0
Observed height = 32° 29′,0
