Hertz radians per second. Thus a disc rotating at 60 revolutions per minute (rpm) is said to be rotating at either 2 rad/s "or" 1 Hz, where the former measures the angular velocity and the latter reflects the number of "complete" revolutions per second. The conversion between a frequency "f" measured in hertz and an angular velocity "ω" measured in radians per second is The hertz is named after the German physicist Heinrich Hertz (1857–1894), who made important scientific contributions to the study of electromagnetism. The name was established by the International Electrotechnical Commission (IEC) in 1930. It was adopted by
Astronomical unit expanding outward from the Sun. This has led to calls to abandon the astronomical unit as a unit of measurement. As the speed of light has an exact defined value in SI units and the Gaussian gravitational constant "k" is fixed in the astronomical system of units, measuring the light time per unit distance is exactly equivalent to measuring the product "G" in SI units. Hence, it is possible to construct ephemerides entirely in SI units, which is increasingly becoming the norm. A 2004 analysis of radiometric measurements in the inner Solar System suggested that the secular increase in the