A digital sextant

Sextants are wonderfully analog optical devices. A sextant user from the 1850s would have little problem using a modern sextant. Now a company in South Korea has begun offering something it calls the Korea Digital Sextant (KDS) that digitalizes…

BioBase by C-MAP Launches New Subscription Model

Egersund, Norway – C-MAP®, a leader in digital marine cartography and cloud-based mapping, announced today it has opened its BioBase™ EcoSound™ platform to include free subscriptions to qualifying organizations. Owned by Navico and operated through C-MAP, BioBase is a platform for aquatic…

Celestial navigation series, part 12

In this installment, we’ll discover moon sights and how they add a useful celestial body to your arsenal. We will also look at how to use celestial navigation techniques to determine your vessel’s compass deviation.

Celestial navigation series, part 10

In this installment, we’ll cover how to reduce a planet sight; we’ll include a step-by-step breakdown of how to reduce star and planet sights, and we will also include a star sight problem to solve as a way to review what you learned in the last installment.

The wandering magnetic pole

The Earth’s Magnetic North Pole, where the lines of magnetic force enter the Earth perpendicular to the globe’s surface, is actually a wandering location.

Celestial navigation series, part four

In this installment, we’ll cover Local Hour Angle (LHA), and determining assumed longitude and assumed latitude. We’ll also look at the spherical trigonometric process for doing sight reduction.

Celestial navigation series, part three

In this installment, we’ll discuss the navigational astronomy of the sun, the celestial sphere, the coordinate system used on the celestial sphere and also the navigational triangle.

Celestial navigation series, part two

In this installment, we’ll discuss how to make our own chart for plotting our celestial navigation data at sea, and we’ll review dead reckoning, plotting, current vectors and compensating for current.

Celestial navigation series, part one

We’re revisiting this series on navigating by the sun, moon, stars and planets in the age of GPS because celestial nav is not only a viable backup to satellite navigation, but it is also a skill that ocean voyagers should have in their toolkit.

More than zoom levels

Aboard our Dufour ketch Terrapin, we use Navionics on our Raymarine chartplotter and also have two Android tablets with the Navionics app as well as OpenCPN with Google Earth charts.

Lunitidal interval

In the small village where I live, I have spread my reputation as someone who knows a thing or two about celestial navigation.


According to my well-thumbed and trusty 2016 Nautical Almanac, the declination of the sun was at its northernmost point at 1400 hours on June 20 when it climbed to 23° 26.1’, and it stayed there — as if resting on a rock after a long climb, catching its breath admiring the view — until June 21, when between 0700 and 0800 it roused itself, shook off the cobwebs and moved south 0.1’.