Parallax Moon

MARITIME – CELETIAL NAVIGATION CALCULATOR Parallax Moon A precise tool.
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What is the Parallax Moon & How does it work?

In celestial navigation the Moon is close enough to Earth that its observed altitude is affected by parallax – the apparent shift caused by the observer’s position on the rotating globe. The amount of shift depends on the Moon’s horizontal parallax (HP), the observer’s latitude (Ο†) and the azimuth of the Moon at the moment of the sight.

The parallax correction is added to the raw observed altitude (Ho) to obtain a parallax‑free altitude that can be used with the sight reduction tables. Because the Moon moves quickly, this correction is usually the largest of any celestial body.

The correction formula is derived from spherical trigonometry and can be expressed as:

\Delta P = HP cdot cos(phi) cdot sin(Az)
Delta P = parallax correction in altitude (Β°)
HP = horizontal parallax of the Moon (Β°)
phi = observer latitude (Β°)
Az = azimuth of the Moon (Β°)
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Frequently Asked Questions
What is parallax correction in celestial navigation?
Parallax correction adjusts the observed altitude of the Moon to account for the observer’s position on Earth, providing a more accurate altitude for navigation.
How does the Moon’s horizontal parallax affect observations?
The Moon’s horizontal parallax causes an apparent shift in its position when viewed from different locations on Earth, which needs to be corrected for precise navigation.
What factors are considered in calculating parallax correction?
Parallax correction takes into account the Moon’s horizontal parallax, the observer’s latitude, and the azimuth of the Moon at the time of observation.
Why is it important to correct for parallax when observing the Moon?
Correcting for parallax ensures accurate altitude measurements, which are crucial for celestial navigation and determining a ship’s position.
How do I use this calculator to get the parallax correction?
Enter the Moon’s horizontal parallax, your latitude, and the azimuth of the Moon into the calculator. It will then provide you with the necessary parallax correction.

Results are for informational purposes only and do not constitute professional advice.