A weather vane is an instrument for showing the direction of the wind. They are typically used as an architectural ornament to the highest point of a building.
Although partly functional, weather vanes are generally decorative, often featuring the traditional cockerel design with letters indicating the points of the compass. Other common motifs include ships, arrows and horses. Not all weather vanes have pointers.
The word 'vane' comes from the Anglo-Saxon word 'fane' meaning 'flag'.
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The design of a wind vane is such that the weight is evenly distributed on each side of the surface, but the surface area is unequally divided, so that the pointer can move freely on its axis. The side with the larger surface area is blown away from the wind direction, so that the smaller side, with the pointer, is pivoted to face the wind direction. Most wind vanes have directional markers beneath the arrow, aligned with the geographic directions.
Wind vanes, especially those with fanciful shapes, do not always show the real direction of a very gentle wind. This is because the figures do not achieve the necessary design balance: an unequal surface area but balanced in weight.
To obtain an accurate reading, the wind vane must be located well above the ground and away from buildings, trees, and other objects which interfere with the true wind direction. Changing wind direction can be meaningful when coordinated with other apparent sky conditions, enabling the user to make simple short range forecasts. From the street level the size of many weathercocks is deceptive.[1]
The Tower of the Winds on the ancient Roman agora in Athens once bore on its roof a wind vane in the form of a bronze Triton holding a rod in his outstretched hand, rotating as the wind changed direction. Below, the frieze was adorned with the eight wind deities. The eight metre high structure also featured sundials, and a water clock inside dates from around 50 BC.[2]
In the 9th century the Pope issued an edict that all churches must show the symbol of a cock on its dome or steeple, as a symbol of Jesus' prophecy of Peter's betrayal (Luke 22:34), that Peter would deny him three times before the rooster crowed on the morning following the Last Supper. Many churches started using this symbol on its weathervanes.
The Bayeux Tapestry of 1070s depicts a scene, with a man installing a weather vane with a cock on Westminster Abbey, while the dead King Edward is carried inside.
Early weather vanes had very ornamental pointers, but modern wind vanes are usually simple arrows that dispense with the directionals because the instrument is connected to a remote reading station. An early example of this was installed in the Royal Navy's Admiralty building in London - the vane on the roof was mechanically linked to a large dial in the boardroom so senior officers were always aware of the wind direction when they met.
Modern aerovanes combine the directional vane with an anemometer (a device for measuring wind speed). Co-locating both instruments allows them to use the same axis (a vertical rod) and provides a coordinated readout.
Another wind direction device is the windsock used at airports to show wind direction and strength. The wind fills the sock and makes it blow away from the prevailing wind. Strong winds make the sock point almost horizontally, while light airs allow the sock to hang limply. Because of its size, the windsock can often be seen from the air as well as the ground. Even the most technologically-advanced airports still use windsocks.
According to the Guinness World Records, the world's largest weather vane is a Tío Pepe sherry advertisement located in Jerez, Spain. The city of Montague, Michigan also claims to have the largest standard-design weather vane, being a ship and arrow which measures 48 feet tall, with an arrow 26 feet long.[3]
A challenger for the title of world's largest weather vane is located in Whitehorse, Yukon. The weather vane is a retired Douglas DC-3 CF-CPY atop a swiveling support. Located at the Yukon Transportation Museum [1] beside Whitehorse International Airport, the weather vane is used by pilots to determine wind direction, used as a landmark by tourists and enjoyed by locals. The weather vane only requires a 5 knot wind to rotate.[4]
The term "weathervane" is also a slang word for a politician who has frequent changes of opinion. The National Assembly of Quebec has banned use of this slang term as a slur after its use by members of the legislature.[5]
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