Star Compass.

Frequently asked questions.

What is magnetic declination?

Magnetic declination is the horizontal angle between the direction a compass needle points (magnetic north) and the direction of true geographic north (the North Pole). It exists because Earth's geographic axis and magnetic axis are not the same — the magnetic pole is currently located in the Canadian Arctic, several hundred kilometres from the geographic pole, and it drifts by tens of kilometres every year. Declination varies dramatically by location: in parts of central Europe it is close to zero; in eastern Australia it is about 12° east; on the west coast of North America it ranges from 13–16° east; in eastern Canada it can be 20°+ west. This tool calculates your declination from your GPS coordinates so you always have the correct local value.

How do I find true north with a compass?

To convert a magnetic compass bearing to a true bearing, you apply your local magnetic declination. If your declination is east (positive), true north is to the right of your compass needle by that amount — so add the declination to your compass reading. If your declination is west (negative), true north is to the left — subtract the declination. For example: if your compass reads 0° (magnetic north) and your declination is +15° east, true north is at 15° on your compass dial. This Star Compass tool handles all of this automatically — the Polaris direction shown is already the true north bearing, with declination applied, so you don't need to do any arithmetic.

Why is Polaris special for navigation?

Polaris, also called the North Star or Pole Star, occupies an almost uniquely useful position in the sky: it sits within about 0.7° of Earth's celestial north pole — the point directly above Earth's geographic North Pole. Because of this, as Earth rotates over 24 hours, Polaris traces an extremely small circle (less than 1.4° in diameter) around the celestial pole while every other star traces a much larger arc. To a naked-eye observer, Polaris appears completely stationary. This makes it the only star you can always rely on for a fixed north bearing throughout the night, every night of the year. All other navigational stars rise and set or change altitude significantly as the night progresses.

How are visible stars calculated?

We use a catalogue of the 12 brightest naked-eye stars (Sirius, Canopus, Arcturus, Vega, Capella, Rigel, Procyon, Betelgeuse, Achernar, Hadar, Altair, and Acrux) and calculate each star's altitude above your local horizon using standard astronomical coordinate transformation formulas. The calculation takes your GPS latitude and longitude, the current UTC time, and the star's right ascension and declination (its fixed celestial coordinates) to produce an altitude and azimuth for your exact location right now. Stars are listed when they are above 15° altitude — below that threshold, atmospheric refraction and horizon obstructions make them difficult to observe reliably.

Navigating by the Stars — Polaris and True North

Before magnetic compasses became common, sailors and explorers navigated by the stars — and the technique still works today with nothing more than clear skies and the knowledge of where to look. The Star Compass takes that ancient skill and brings it to your browser: it shows you the direction of Polaris (the North Star), your local magnetic declination, and which of tonight's brightest stars are currently visible above your horizon.

Why Polaris points north

Earth rotates on an axis that is tilted 23.5° relative to its orbit around the sun. That axis points, very nearly, at the star Polaris in the constellation Ursa Minor (the Little Bear). As Earth spins, every star in the sky appears to trace a circle around this point — but Polaris is so close to the axis (within about 0.7°) that it barely moves. Step outside on any clear night in the Northern Hemisphere and Polaris is always in the north, at an altitude above the horizon equal to your latitude. At the North Pole (latitude 90°), Polaris is directly overhead. At the equator (latitude 0°), Polaris sits on the northern horizon.

This relationship makes Polaris unique as a fixed navigational reference. Unlike the Sun or Moon, which move across the sky throughout the day, Polaris stays put. A bearing taken toward Polaris is a true north bearing — not magnetic north, not grid north, but the actual geographic direction toward the North Pole.

Magnetic declination explained

Earth has two distinct north poles. Geographic north (true north) is the geometric North Pole — where Earth's rotation axis meets the surface at latitude 90°N. Magnetic north is where Earth's magnetic field lines converge and point vertically downward, currently located in the Canadian Arctic and slowly drifting a few dozen kilometres per year.

The angle between these two directions, measured from your current position, is your magnetic declination. In London, declination is about 0.5° west — negligible. On the west coast of the United States it can be 14–16° east, meaning a compass pointing "north" actually points toward what a map would call NNW. Ignoring declination in navigation can lead you significantly off-course over distance. The Star Compass calculates your declination from your GPS coordinates using a simplified geomagnetic model and applies it automatically so the Polaris bearing is always shown relative to true north.

Tonight's bright stars

The tool lists the brightest stars that are currently above 15° altitude from your location — high enough to be visible even with some light pollution and atmospheric haze near the horizon. Each star's name, constellation, and current altitude are displayed. The list updates based on your GPS latitude, longitude, and the current time, so it reflects exactly what you would see looking up right now.

Some of the stars you may see listed: Sirius in Canis Major is the brightest star in the night sky (magnitude −1.46) and is easy to spot as a very bright blue-white point in winter. Arcturus in Boötes is the brightest star in the Northern Hemisphere and has a distinctive warm orange colour. Vega in Lyra forms one corner of the Summer Triangle and is prominent in northern summer skies. Rigel and Betelgeuse anchor the iconic constellation Orion, visible from almost everywhere on Earth in winter months.

Using the Star Compass for navigation

The compass dial shows both the direction your device is pointing (the heading needle) and the direction to Polaris (the star ray). To face true north, rotate your body until the two needles align. To walk on a specific true bearing — say, 60° (ENE) — find Polaris direction, add 60°, and face that way. Because Polaris gives true north, any bearing you take from it is already corrected for magnetic declination with no manual arithmetic required.

On a cloudy night or before astronomical twilight ends, the star list may be shorter or empty, but the Polaris direction is still calculated from your GPS coordinates and displayed correctly using the magnetic declination offset. The compass heading remains available from the magnetometer as long as your device has one.