Polaris: a true-north mark in the sky
1The lesson in plain words
Polaris lies about 0.6° from the north celestial pole. At mid-latitudes its bearing stays close to north; use the almanac for its true azimuth.
Why Polaris
Polaris, the Pole Star, is the bright star almost exactly above the Earth's North Pole. Its distance from the celestial pole, its polar distance, is about 0.62° in 2026, roughly 37′, and still shrinking slowly until about 2100. As the Earth turns, Polaris circles the pole in that tiny circle once a day. At mid-latitudes, its true azimuth, or true bearing, stays close to 000°.
How far from north
The azimuth's largest swing depends on your latitude: sin (largest azimuth) = sin (polar distance) ÷ cos (latitude). In 2026 that is about 0.6° at the equator, 0.8° at 40°N, 1.0° at 50°N and 1.2° at 60°N. So taking Polaris as exactly north can give an error of up to about a degree at Spanish latitudes; fine for a rough check, not for a deviation card.
Finding it
Polaris is a medium-bright star, not the brightest in the sky. Find the Plough (Big Dipper), a seven-star ladle shape. Follow the bowl's outer edge from its base through its rim, then continue about five star-separations to Polaris. These two stars are the pointers. Its altitude (angle above the horizon) is almost your northern latitude: about 40° off Valencia, low near the equator. Polaris is normally unavailable for navigation south of the equator.
The exact azimuth
The Nautical Almanac gives Polaris's true azimuth using your latitude and LHA Aries, the local hour angle of Aries. Aries is a reference point on the celestial equator. GHA Aries, its Greenwich hour angle, measures its angle west from Greenwich; LHA measures it west from your meridian. Take GHA Aries for the bearing's UT (Universal Time). Add east longitude or subtract west longitude. Add or subtract 360° if needed to keep LHA from 000° up to, but not including, 360°.
Latitude, in one line
The same tables also correct Polaris's altitude, measured with a sextant, into your latitude; the celestial units explain the method.
2Key data
- Polar distance (2026)
- About 0.62°, roughly 37′
- Largest azimuth swing
- sin Z = sin p ÷ cos lat: about 0.8° at 40°N
- Altitude
- Almost equal to your latitude
- LHA Aries
- GHA Aries + east longitude − west longitude; wrap to 000°–<360°
- Almanac table
- Polaris azimuth by LHA Aries and latitude
- Spanish terms
- Estrella Polar, azimut verdadero, horario de Aries
3Key points
- 1
Polaris is about 0.6° from the celestial pole; its azimuth is close to 000° at mid-latitudes.
- 2
The swing grows with latitude: about 0.8° at 40°N, 1.2° at 60°N.
- 3
Its altitude is almost your northern latitude; it is normally unavailable for navigation south of the equator.
- 4
For an exact true azimuth, enter the almanac's Polaris table with LHA Aries and latitude.
4Frequent mistakes
Wrong: Polaris is exactly at true north.
Right: It circles the pole at about 0.6°. Its azimuth swings up to about a degree either side at mid-latitudes.
Wrong: Polaris is the brightest star in the sky.
Right: It is only medium-bright. Find it from the Plough's pointers or from Cassiopeia.
Wrong: Enter the Polaris table with your longitude.
Right: Enter it with the LHA of Aries, worked out from the almanac's GHA Aries and your longitude, and with your latitude.
5Practice case & exam keys
Off the coast at 41°N, a crew member suggests checking the steering compass by taking Polaris as due north, 000°T. How large an error could that cause, and how do you avoid it?
Show the answer
At 41°N Polaris's azimuth can be up to about 0.8° either side of north, depending on the time. Taking it as 000° could put that much error into your compass check. Note the UT of the bearing, find LHA Aries from the almanac and your longitude, and read the true azimuth from the Polaris table.
Exam keys
- Polaris: polar distance about 0.6° (37′ in 2026); azimuth near 000° at mid-latitudes.
- Largest azimuth ≈ polar distance ÷ cos latitude.
- True azimuth from the almanac's Polaris table, by LHA Aries and latitude.
- LHA Aries = GHA Aries ± longitude (east +, west −); wrap to 000°–<360°.
Finish this unit
When you've read it, match the terms, then answer three questions. Get them all right to finish the unit; opening the page alone doesn't count.
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