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He used trigonometry to calculate the radius of the Earth using measurements of the height of a hill and measurement of the dip in the horizon from the top of that hill. His calculated radius for the Earth of 3928.77 miles was 2% higher than the actual mean radius of 3847.80 miles. [19]
According to a study in France, executives and professionals are 2.6 centimetres (1.0 in) taller, and university students are 2.55 centimetres (1.0 in) taller than the national average. [ 7] As this case shows, data taken from a particular social group may not represent a total population in some countries.
Around 830 AD, Caliph Al-Ma'mun commissioned a group of Muslim astronomers and Muslim geographers to perform an arc measurement from Tadmur to Raqqa, in modern Syria.They found the cities to be separated by one degree of latitude and the corresponding meridian arc distance to be 66⅔ Arabic miles and thus calculated the Earth's circumference to be 24,000 miles (39,000 km).
Pressure as a function of the height above the sea level. The human body can perform best at sea level, [7] where the atmospheric pressure is 101,325 Pa or 1013.25 millibars (or 1 atm, by definition). The concentration of oxygen (O 2) in sea-level air is 20.9%, so the partial pressure of O 2 (pO 2) is 21.136 kilopascals (158.53 mmHg).
Altitude is a distance measurement, usually in the vertical or "up" direction, between a reference datum and a point or object. The exact definition and reference datum varies according to the context (e.g., aviation, geometry, geographical survey, sport, or atmospheric pressure). Although the term altitude is commonly used to mean the height ...
An alternative is to base height measurements on a reference ellipsoid approximating the entire Earth, which is what systems such as GPS do. In aviation, the reference ellipsoid known as WGS84 is increasingly used to define heights; however, differences up to 100 metres (328 feet) exist between this ellipsoid height and local mean sea level. [ 5 ]
The North Tower was 417 m (1,368 ft) and the South Tower 415 m (1,362 ft) tall. It surpassed the height of the Empire State Building by 36 m (118 ft). Two years later the Sears Tower was built in Chicago, standing at 442 m (1,450 ft) with 110 floors, surpassing the height of the World Trade Center by 25 m (82 ft).
Height above mean sea level is a measure of a location's vertical distance (height, elevation or altitude) in reference to a vertical datum based on a historic mean sea level. In geodesy, it is formalized as orthometric height. The zero level varies in different countries due to different reference points and historic measurement periods.