Finding north and south
with nothing but the sky.

For most of history, people found their way at night by reading the sky. You probably will not need to navigate a ship by the stars, but knowing which way is north or south is surprisingly useful. It helps you orient a star chart, predict where the Moon and planets will rise, and know which part of the horizon to watch for a space station pass. It is also deeply satisfying to look up and know where you are facing.

This field note covers the classic methods for both hemispheres. None needs any equipment.

Why the sky turns around two points

As Earth rotates, the whole sky appears to turn once a day around two points directly above Earth's poles: the north and south celestial poles. Stars near those points trace small circles and never set. Stars further away rise in the east and set in the west. If you can find the point the sky turns around, you have found north or south.

How high that point sits above your horizon depends on your latitude. The Open University notes that from southern England, the north celestial pole is about 52 degrees above the horizon, matching the latitude of about 52 degrees north. At the equator, both poles lie on the horizon. This also means that from the southern hemisphere you cannot see the north celestial pole at all, and vice versa.

Northern hemisphere: find Polaris with the Big Dipper

In the northern sky, a moderately bright star called Polaris, the North Star, sits very close to the north celestial pole. It is not the brightest star in the sky, so the trick is to find it with a familiar pattern.

The Big Dipper, also called the Plough, is a group of seven bright stars in the constellation Ursa Major. Four stars form a bowl and three form a handle.

1. Find the two stars at the end of the bowl, furthest from the handle. They are called Dubhe and Merak, or simply the pointers.
2. Draw an imaginary line from Merak, at the bottom of the bowl, through Dubhe, at the top.
3. Extend that line about five times the distance between the two stars.
4. The first reasonably bright star you reach is Polaris.

Now drop an imaginary line straight down from Polaris to the horizon. That point on the horizon is north. With north in front of you, east is to your right and west to your left.

The Big Dipper turns around Polaris through the night and through the year, so it may be upright, upside down or on its side. The pointers always point to Polaris whatever the orientation. Space.com notes that the Big Dipper is only fully visible from north of about 25 degrees south, so it is low or absent for much of the southern hemisphere.

Southern hemisphere: find south with the Southern Cross

There is no bright star at the south celestial pole. The nearest naked-eye star, Sigma Octantis, is so faint that the Astronomical Society of Southern Africa describes it as on the threshold of visibility even under dark skies. Instead, southern observers use Crux, the Southern Cross, and two bright stars beside it.

Crux is the smallest of the 88 constellations, but its four main stars make a compact kite shape. Next to it are two very bright stars in Centaurus, Alpha and Beta Centauri, often called the pointers. They help confirm you have the real Southern Cross and not the larger "False Cross" made of stars in Vela and Carina.

Method 1: follow the long axis

1. Find the long axis of the cross, from Gacrux at the top to Acrux at the foot.
2. Extend that line beyond Acrux by about four and a half times the length of the cross.
3. That point in the sky is close to the south celestial pole.
4. Drop a line straight down to the horizon. That is approximately south.

Method 2: use the pointers as a check

Draw a line between Alpha and Beta Centauri, find its midpoint, and draw a second line at right angles from that midpoint, away from the cross. Where this line crosses the extended line from the Southern Cross is close to the south celestial pole. The ASSA recommends using both methods and checking that they agree, because neither is perfect.

From South Africa and much of Australia, the Southern Cross is visible for most of the year. South of about 34 degrees south it never sets, though it may sit low over the southern horizon on autumn and spring evenings.

Anywhere: use Orion's belt for east and west

Orion is one of the few constellations that is easy to recognize from both hemispheres. It is best seen in the evening from about December to March. The three bright stars of its belt lie very close to the celestial equator, the line in the sky above Earth's equator.

This gives a simple rule. Stars on the celestial equator rise almost exactly due east and set almost exactly due west, wherever you are on Earth. So when Orion's belt is low on the horizon, rising or setting, it marks east or west. The westernmost belt star, Mintaka, is the closest to the celestial equator and gives the best line.

Practical tips

• Learn the patterns at home. Spend a few evenings identifying the Big Dipper or the Southern Cross before you need them. The darkness planner shows when your sky is dark enough.
• Check against a known landmark. Compare your star-based direction with a street that you know runs north to south. This builds confidence.
• Remember it is approximate. These methods will get you within a few degrees. That is plenty for orienting a star chart or picking a viewing spot, but serious navigation needs a map and compass as well.
• Watch for clouds and terrain. A single cloud can hide the cross or the pointers. Knowing more than one method lets you work around gaps.

If you are new to stargazing, our dark sky field note explains how to let your eyes adapt, and the planet guide helps when a bright point does not match any constellation you know.