Natural disasters in Japan shaking we call an earthquake. Earthquakes can cause shaking that could last seconds or minutes. Besides that, there may be several earthquakes over a period ranging from hours to weeks called aftershocks, and the magnitude of the following tremors will decrease with time. It is important to know the earthquake magnitude because it can be the clue if there will be any aftershocks. Because of that, magnitude can be measured on the Richter scale, invented by Charles F. Richter in 1934. The Richter magnitude is calculated from the amplitude of the largest seismic wave recorded for the earthquake. In the
Absolute magnitude corresponds to absolute bolometric magnitude 4.74. Placing a radiation source (e.g. star) at the standard distance of 10 parsecs, it follows that the zero point of the apparent bolometric magnitude scale corresponds to irradiance . Using the IAU 2015 scale, the nominal total solar irradiance ("solar constant") measured at 1 astronomical unit () corresponds to an apparent bolometric magnitude of the Sun of −26.832. Following Resolution B2, the relation between a star's absolute bolometric magnitude and its luminosity is no longer directly tied to the Sun's (variable) luminosity: where The new IAU absolute magnitude scale permanently disconnects the scale from