MARITIME – CELETIAL NAVIGATION CALCULATOR
Celestial Altitude
A precise tool.
What is the Celestial Altitude & How does it work?
Celestial altitude is the angle measured between a celestial body and the visible horizon. In maritime navigation it provides a direct link between the observer’s position on Earth and the known coordinates of stars, the Sun, or planets, allowing a navigator to determine latitude and, when combined with time, longitude. The raw measurement taken with a sextant is called the observed altitude (Ho). Because the instrument, the observer’s eye height, and atmospheric refraction all introduce systematic errors, the observed altitude must be corrected before it can be used in the sight reduction tables. The corrected altitude (Hc) is obtained by applying a series of small adjustments: the instrument correction (IC) derived from the index error, the dip correction (D) for the height of eye above sea level, and the refraction correction (R). The relationship is expressed by a simple linear formula.
H_c = H_o + I_C – D – R
H_c = corrected altitude; H_o = observed altitude; I_C = instrument correction (‑index error); D = dip; R = refraction
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Frequently Asked Questions
What is celestial altitude in maritime navigation?
Celestial altitude is the angle between a celestial body and the horizon, used to determine latitude and longitude.
How do I measure observed altitude with a sextant?
Align the sextant’s horizon mirror with the celestial body and read the angle from the scale.
Why is eye height important in celestial navigation?
Eye height corrects for the observer’s position above sea level, affecting the apparent altitude of celestial bodies.
How does atmospheric refraction affect celestial measurements?
Atmospheric refraction bends light rays, causing celestial bodies to appear higher in the sky than they actually are.
Can I use this calculator for any celestial body?
Yes, you can calculate the altitude for stars, the Sun, or planets using this tool.
What is the difference between observed and true altitude?
Observed altitude is the raw measurement taken with a sextant, while true altitude accounts for corrections like eye height and refraction.
How do I use this calculator to find my latitude?
Input the observed altitude, eye height, and atmospheric correction factor to calculate your latitude.
Results are for informational purposes only and do not constitute professional advice.