when was it introduced?
1960
International System of Units
The International System of Units, the SI, is a decimal and metric system of units established in 1960 and periodically updated since then.
characteristics of stars based on the characteristics of the sun A star with mass greater than 0.4 times the Sun's will expand to become a red giant when the hydrogen fuel in its core is exhausted. have these been observed since ancient times? UNANSWERABLE how are they measured? It is often most convenient to express mass, luminosity, and radii in solar units could you please explain the second term? It is an absolute measure of radiated electromagnetic power, the radiant power emitted by a light-emitting object. howe is it measured? In SI units, luminosity is measured in joules per second, or watts and in astronomy, in the terms of the luminosity of the Sun, L how is it measured for a star? By its size in terms of solar radii, R, and effective temperature in kelvins what is this last unit that you mentioned? It is the base unit of temperature in the International System of Units (SI) why was it redefined? So that Boltzmann constant takes the exact value by whom was this unit formulated? William Thomson, later ennobled as Lord Kelvin you mentioned about an international system earlier, what is it? It is the modern form of the metric system; only system of measurement with an official status in nearly every country in the world.
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International System of Units [SEP] Introduction
The International System of Units, the SI, is a decimal and metric system of units established in 1960 and periodically updated since then. The SI has an official status in most countries, including the United States and the United Kingdom, with these two countries being amongst a handful of nations that, to various degrees, continue to resist widespread internal adoption of the SI system. As a consequence, the SI system “has been used around the world as the preferred system of units, the basic language for science, technology, industry and trade.” The only other types of measurement system that still have widespread use across the world are the Imperial and US customary measurement systems, and they are legally defined in terms of the SI system.