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Many mechanical aids to calculation and measurement were constructed for astronomical and navigation use. The planisphere was a star chart invented by Abu Rayhan al-Biruni in the early 11th century. The astrolabe was invented in the Hellenistic world in either the 1st or 2nd centuries BC and is often attributed to Hipparchus. A combination of the planisphere and dioptra, the astrolabe was effectively an analog computer capable of working out several different kinds of problems in spherical astronomy. An astrolabe incorporating a mechanical calendar computer and gear-wheels was invented by Abi Bakr of Isfahan, Persia in 1235. Abu Rayhan al-Biruni invented the first mechanical geared lunisolar calendar astrolabe, an early fixed-wired knowledge processing machine with a gear train and gear-wheels, circa 1000 AD.

Who is thought to have invented the astrolabe in history?
Answer: Hipparchus
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Nanjing, with a total land area of 6,598 square kilometres (2,548 sq mi), is situated in the heartland of drainage area of lower reaches of Yangtze River, and in Yangtze River Delta, one of the largest economic zones of China. The Yangtze River flows past the west side and then north side of Nanjing City, while the Ningzheng Ridge surrounds the north, east and south side of the city. The city is 300 kilometres (190 mi) west-northwest of Shanghai, 1,200 kilometres (750 mi) south-southeast of Beijing, and 1,400 kilometres (870 mi) east-northeast of Chongqing. The downstream Yangtze River flows from Jiujiang, Jiangxi, through Anhui and Jiangsu to East Sea, north to drainage basin of downstream Yangtze is Huai River basin and south to it is Zhe River basin, and they are connected by the Grand Canal east to Nanjing. The area around Nanjing is called Hsiajiang (, Downstream River) region, with Jianghuai () stressing northern part and Jiangzhe () stressing southern part. The region is also known as Dongnan (, South East, the Southeast) and Jiangnan (, River South, south of Yangtze).

What is the name of the area of land around Nanjing?
Answer: Hsiajiang (, Downstream River) region
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Sahih al-Bukhari narrates Muhammad describing the revelations as, "Sometimes it is (revealed) like the ringing of a bell" and Aisha reported, "I saw the Prophet being inspired Divinely on a very cold day and noticed the sweat dropping from his forehead (as the Inspiration was over)." Muhammad's first revelation, according to the Quran, was accompanied with a vision. The agent of revelation is mentioned as the "one mighty in power", the one who "grew clear to view when he was on the uppermost horizon. Then he drew nigh and came down till he was (distant) two bows' length or even nearer." The Islamic studies scholar Welch states in the Encyclopaedia of Islam that he believes the graphic descriptions of Muhammad's condition at these moments may be regarded as genuine, because he was severely disturbed after these revelations. According to Welch, these seizures would have been seen by those around him as convincing evidence for the superhuman origin of Muhammad's inspirations. However, Muhammad's critics accused him of being a possessed man, a soothsayer or a magician since his experiences were similar to those claimed by such figures well known in ancient Arabia. Welch additionally states that it remains uncertain whether these experiences occurred before or after Muhammad's initial claim of prophethood.

What measure of distance described the nearness of the Angel's approach to Mohammad?
Answer:
two bows' length