The didgeridoo, developed by the Australian Aborigines, is perhaps the world’s oldest wind instrument. Though the exact age of the didgeridoo is unknown, studies of rock art in northern Australia suggest that the Aboriginal people have been using it for approximately 1,500 years. Didgeridoos measure about 4 ft (1.5 m) in length and are made from branches that have been hollowed out by termites. A 2005 study found that practicing the didgeridoo can help reduce what sleep-related conditions? Discuss
Source: The Free Dictionary
Distinguished by its size and rising succession of domes, the Hagia Sophia is the supreme masterpiece of Byzantine architecture. First a church, later a mosque, and now a museum, it was designed under Justinian I by Anthemius of Tralles and Isidorus of Miletus and completed in less than six years. Its combination of a longitudinal basilica with a main building was wholly original in the sixth century, as was its use of pendentives. The Hagia Sophia stands on the site of what earlier structure? 
American conservationist 
Dietrich was a German actress and singer. Abandoning an early ambition to be a violinist, she turned to acting and gained international attention as a femme fatale in The Blue Angel (1930). She then moved to Hollywood, where she starred in a series of films that established her glamorous and sophisticated persona. Resisting Nazi pressure to return to Germany, she became a US citizen in 1939. During WWII, she regularly entertained Allied troops, appearing before them how many times? 
High-speed photography allows fast moving phenomena to be recorded with precision and clarity. While in 1948 high-speed photography was defined as a set of at least 3 photographs taken by a camera capable of recording a minimum of 128 frames per second, today’s equipment can shoot as many as 1 million frames per second. High-speed photography was first put to practical use in 1878 to investigate whether or not a trotting horse ever has all 4 feet off the ground at once. What did the images show? 
Why is it that when you awake to the world of realities you nearly always feel, sometimes very vividly, that the vanished dream has carried with it some enigma which you have failed to solve?