Make a weather vane

Follow these instructions to make your own weather vane and learn why it's useful to know which direction the wind is blowing.

• 7 May 2007 | Updated 14 October 2011

• What you need
• What to do
• What’s happening
• Did you know

The weather vane or wind vane is one of the oldest tools for monitoring the weather. Wind direction tells you what the wind will be like. For example, in the southern hemisphere, a south wind is cold and a north wind is warm. (A north wind blows from the north.)

The part of the vane that turns into the wind is often shaped like an arrow. The blunt end is made wide so it will move in the gentlest breeze. Here's how you can make your own weather vane.

Note: this wind vane works best in a light wind. If you intend to use the wind vane in a very light breeze, then thin cardboard is best. For stronger winds, use stronger cardboard, or you can use a light wood such as plywood.

What you need

To make a cardboard weather vane you will need:

• cardboard (an old cardboard box will do)
• ruler and pencil
• scissors
• pin
• five- or ten-cent coin
• sticky tape
• cotton thread (about 30 centimetres long).

What to do

1. Using the diagram below, mark out an arrow on your cardboard, then cut it out.
2. Tape the coin to the head of the arrow near the tip.
3. Hold the arrow lightly by its top edge. The tip of the arrow will probably dip down or move up. Hold the arrow at different points along its length until the arrow stays straight (parallel to the floor). This is a rough estimate of the arrow’s balance point. The balance point will be closer to the tip of the arrow than to the blunt end.
4. Stick the pin into the card at the balance point, about 0.5 centimetres in from the edge. If the arrow dips at either end when you hold the pin, you are not quite on the balance point. Move the pin until it balances parallel to the floor.
5. Make the pinhole a little bigger, thread the cotton through the hole and tie the end to the arrow.

Now you can take the vane outside and either hold it away from your body, or hang it in a tree and watch what happens.

Cut your weather vane out of cardboard according to these measurements.

What’s happening

Weather vanes are usually placed high on buildings because the wind blows more steadily out of the way of buildings and trees. Down near the ground the wind can become turbulent and blow every which way. So if the wind is blowing unsteadily, your weather vane will twist and shift as the wind moves.

The arrow always points to the direction the wind is coming from. This occurs because the balance point of the arrow is towards the front (at the pointy end). You shifted the balance point to this end by sticking the coin to it. This leaves a large surface area at the back of the arrow for the wind to push against. The wind pushes against the back of the arrow until it catches both sides equally. At this time, the arrow will be relatively still and the arrow will be pointing directly into the wind.

Did you know

The word 'vane' comes from the Anglo-Saxon word ‘fane’, which means flag.

English weather vanes probably developed from flags or banners, which flew from medieval towers to show archers the wind direction, so they could shoot more accurately.

By Philippa Rowlands

For more hands-on activities, join CSIRO's Double Helix Science Club.