Finding direction by the stars: North Star and Southern Cross

Because the Earth rotates, all the stars seem to travel in circles around two points in the sky: the north and south celestial poles. These points lie straight above the Earth's poles, extended into space. The North Star sits very close to the north celestial pole. That is why it barely changes position during the night while the other stars turn around it.

The North Star's height above the horizon roughly equals your latitude. In central Europe it therefore stands about halfway up the sky, near the equator it hangs just above the horizon, and south of the equator it cannot be seen at all. There is no bright star at the south celestial pole. There you estimate the position of the pole using the Southern Cross, which is somewhat less precise.

A common misconception is that the North Star is the brightest star in the sky. It is not: it is only moderately bright and stands out mainly because it sits fairly alone in its part of the sky. If you simply pick the brightest point in the sky, you often end up with a planet or a completely different star.

In the northern hemisphere the Big Dipper (also called the Plough) is the key. It consists of four stars forming a bowl and three stars forming a handle. The two stars on the outer side of the bowl, opposite the handle, point like an arrow to the North Star; you extend the line between them about five times their separation. If the Big Dipper is low or behind trees, the 'W' of Cassiopeia, which lies on the other side of the North Star, helps.

In the southern hemisphere you must tell the real Southern Cross from the larger 'False Cross'. The real cross is smaller and has two bright companion stars next to it, the 'pointer stars'. You extend the cross's long axis about four and a half times its length and look straight down from that point to the horizon: that is roughly south.

The direction you find is an estimate, not a measurement. In practice it is usually enough to know a rough main direction – for example 'the road lies to the south'. Mark it at once with sticks or stones on the ground. Next morning the sky is bright, and without a marker the direction is forgotten.

The stars are a makeshift when there is no compass or when you want to roughly double-check a direction. They need a clear sky and an open view upward. Under a dense forest canopy, in cloud or thick haze the method does not work. Light pollution near towns can also make fainter stars disappear.

Setting off at night just because you know a direction is usually not a good idea. Unknown terrain is much more dangerous in the dark: ditches, drops and water are seen too late. It is more sensible to find the direction at night, mark it, and set off that way in daylight – ideally towards a large handrail such as a road, a river or a coastline.

Learn the constellations at home or in the garden, not only in an emergency. Go outside on a clear evening, find the Big Dipper and follow the two pointer stars to the North Star. Check the result with a compass. If you do this on several evenings and at different times, you will notice that the Big Dipper is sometimes high, sometimes low and sometimes 'upside down' – but the North Star stays in the same place.

Star charts or astronomy apps help you get started, but the goal is to recognise the constellations without a device. If you travel to the southern hemisphere, have someone there show you the Southern Cross and the False Cross, or compare them on a star chart beforehand.

Stars rise roughly in the east and set in the west, just like the sun. If you watch a star against a fixed point for a while – say a treetop – you can derive a very rough direction from it. But this is much less precise than the North Star.

Star navigation is one of humanity's oldest methods of orientation. Seafarers long used the North Star to estimate their latitude. As a hiker you need a more modest task: finding one main direction so that next day you can head for a large, safe handrail.