Windsock

A windsock or wind cone is a conical textile tube designed to indicate wind direction and relative wind speed.

Wind direction is the opposite of the direction in which the windsock is pointing (note that wind directions are conventionally specified as being the compass point from which the wind originates; so a windsock pointing due north indicates a southerly wind). Windspeed is indicated by the windsock's angle relative to the mounting pole; in low winds, the windsock droops; in high winds it flies horizontally.

Per FAA standards referenced below, a 15 knot (17mph) wind will fully extend the windsock. A 3 knot (3.5mph) breeze will cause the windsock to orient itself according to the wind.

At many airports windsocks are lighted at night, either by flood lights on top surrounding it or with one mounted on the pole shining inside it.



Quoted from Wikipedia