Thermal duration is the traditional method of soaring. In this method a model that is optimized for staying aloft is launched to a height of 600 feet and then set off in search of thermal lift. Thermal lift forms on the ground due to the sun´s energy, it gradually releases from the ground in the form of bubbles or columns of rising air. Thermal duration pilots try to aim their plane to and fly in this lift with the intent to stay aloft as long as possible. On ideal days, staying aloft over an hour is possible. Climbing in lift requires practice. Thermals move around and they change in size. Generally a plane is circled by the pilot to stay centered in the core of the lift, much like a soaring bird. Strong thermals will allow a model to gain well over 100 feet in altitude per minute.