What is a Weathervane and how does work?
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, weathervanes are generally decorative, often featuring the traditional cockerel design with letters indicating the points of the compass. The word 'vane' comes from the Anglo-Saxon word 'fane' meaning 'flag'.
The design of a wind vane is such that the weight is evenly distributed 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 area is blown away from the wind direction. The pointer is therefore always on the smaller side (a north wind is one that blows from the north). 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.