Navigation Using The Night Sky

By Ed Jones

Ever wondered how people found their way at night before GPS? Before we had satellites and google maps to guide our way, humans had to rely on more natural sources for directions, namely, the stars. Using the night sky for navigation is a very handy tool to have. Here are several ways to find directions using the night sky.

Finding South

If you visit the Perth Observatory, we will show you how to find South using the southern cross, there are two basic methods:

1. Imagine a line joining the two stars at the “head” and “foot” of the cross. Extend the line out another 4 lengths from the foot of the cross and this will be the position of the South Celestial Pole (SCP).

Look straight down from the SCP to the horizon, you’ve found south!!

2. Another slightly trickier, but more accurate way to find south is to use the Southern Cross and the two pointer stars from the nearby constellation of Centaurus.

Draw a line through the two stars at the head and foot of the cross in the same way as described above (1). Then join the two pointers with a line (2) and draw a perpendicular line (3) towards line 1 and where they intersect is the SCP. Look straight down from the SCP to the horizon, you’ve found south

1. With the moon – quick fix

Imagine a line that connects the horns of a crescent moon and extend this line down to the horizon. In southern latitudes, this will give an approximation of North and works best when the moon is not near the horizon.

2. With the moon – quick fix

Imagine a line that connects the horns of a crescent moon and extend this line down to the horizon. In southern latitudes, this will give an approximation of North and works best when the moon is not near the horizon. With the moon, slower but more accurate method. All celestial objects stars, planets, sun and moon, arc across the northern sky when viewed from southern latitudes.

They all reach their highest point in the sky when they are directly north of you. Provided the object is bright enough to cast a shadow (does not have to be a full moon), place a stake in the ground and mark where the end shadow cast by the tip of the stake is for a period of line. The points will make a curved line and when the shadow is shortest this will be when the object is perfectly due north of you.

3. Using the Constellation of Orion.

Identify Orion’s “belt” and then Orion’s “sword”. (Remember in the Southern Hemisphere the swords “hangs” upwards) Imagine the sword is the shaft of an arrow.

Imagine the “head” of the arrow is the belt and some of the fainter stars. Extend a line from the “arrow” to the horizon and this will be North. As Orion moves across the night shy the “arrow” will continue to point North.

Finding East or West

Orion rises in the East and Sets in the West. Orion’s belt has three stars that form an almost straight line in the night sky. These stars rise very close to due East and set very close to due West.

But – if you want to be really accurate, then the first star to rise (and the last to set) is called Mintaka and will always rise and set within one degree of true east and west wherever you are in the world.

1. Make a fist out of your hand, hold your arm outstretched towards the horizon. Select a bright star at least one fist above the horizon and take two stakes and drive them into the ground about 1 metre apart, lined up on your selected star.

2.

3. Create an imaginary line that connects the stakes’ tops and your star.

Check on your target after a while, the target will have apparently moved (due to the Earth’s rotation), note the direction of movement.

If the star descended, you are looking West.

If the star ascended, you are looking East.

If the star moved to the right, you are looking south.

 If the star moved to the left, you are looking north.

Try these out next time you are somewhere where there is a dark sky.

The big advantages of using the sky over GPS – no batteries to go flat and it works even when you can’t get a signal!!!