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Temperature scale and the Boltzmann constant: The newest system of units is based on a compatible set of natural constants with fixed values. An example is the Boltzmann constant k which defines the thermal energy content kT. To express the base unit T, the absolute temperature in kelvin, an international agreement for the temperature scale is needed. The scale is defined using fixed points, which are temperatures of various phase transitions. Especially important has been the triple point of water at 273.1600 K. These fixed point temperatures determine the international temperature scale ITS within the Si system. Temperature measurement itself is based on physical laws and on the properties of appropriate thermometric materials selected to determine the temperature scale. For determining the Boltzmann constant, new precision techniques have been developed during the last two decades. Examples are different types of gas thermometry, which ultimately are based on the ideal gas law, and thermal noise of electric charge carriers in conductors. With these means it has become possible to fix the value of the Boltzmann constant with a relative uncertainty of < 1 ppm. As of 2019, the value of k has been agreed to be fixed at 1.380649x10^(-23) J/K. This agreement replaces the earlier definition of a Kelvin degree.
In the ancient Egypt seven goddesses, represented by seven cows, composed the celestial herd that provides the nourishment to her worshippers. This herd is observed in the sky as a group of stars, the Pleiades, close to Aldebaran, the main star in th
Indigenous peoples across the world observe the motions and positions of stars to develop seasonal calendars. Additionally, changing properties of stars, such as their brightness and colour, are also used for predicting weather. Combining archival st
Who was Ulugh Beg? A prince who governed a province in the central Asian empire built by his grandfather Tamerlane. Above all, he was a scholar who founded the Samarkand astronomical observatory, whose work predated that of the best astronomers in Europe one and a half centuries later.
A century ago, Srinivasa Ramanujan -- the great self-taught Indian genius of mathematics -- died, shortly after returning from Cambridge, UK, where he had collaborated with Godfrey Hardy. Ramanujan contributed numerous outstanding results to differen
We survey early Indian ideas on the speed of light and the size of the universe. A context is provided for Sayanas statement (14th century)that the speed is 2,202 yojanas per half nimesha (186,000 miles per second!). It is shown how this statement ma