flight was achieved in 1964. New materials such as glass fiber and carbon fiber, advances in wing shapes and airfoils, electronic instruments, the Global Positioning System and improved weather forecasting have since allowed many pilots to make flights that were once extraordinary. Today over 550 pilots have made flights over . Although there is no Olympic competition, there are the World Gliding Championships. The first event was held at the Samedan in 1948. Since World War II it has been held every two years. There are now six classes open to both sexes, plus three classes for women and two junior classes. The latest worldwide statistics for 2011 indicate that Germany, the sport's birthplace, is still a center of the gliding world: it accounted for 27 percent of the world's glider pilots, and the three major glider manufacturers are still based there. However the meteorological conditions that allow soaring are common and the sport has been taken up in many countries. At the last count, there were over 111,000 active civilian glider pilots and 32,920 gliders, plus an unknown number of military cadets and aircraft. Clubs actively seek new members by giving trial flights, which are also a useful source of revenue for the clubs. Soaring Glider pilots can stay airborne for hours by flying through air that is ascending as fast or faster than the glider itself is descending, thus gaining potential energy. The most commonly used sources of rising air are thermals (updrafts of warm air); ridge lift (found where the wind blows against the face of a hill and is forced to rise); and wave lift (standing waves in the atmosphere, analogous to the ripples on the surface of a stream). Ridge lift rarely allows pilots to climb much higher than about above the terrain; thermals, depending on the climate and terrain, can allow climbs in excess of in flat country and much higher above mountains; wave lift has allowed a glider to reach an altitude of . In a few countries such as the UK, gliders may continue to climb into the clouds in uncontrolled airspace, but in many European countries the pilot must stop climbing before reaching the cloud base (see Visual Flight Rules). Thermals Thermals begin as bubbles of rising air that are formed on the ground through the warming of the surface by sunlight. If the air contains enough moisture, the water will