Charles Francis Richter an instrument generally consisting of a constantly unwinding roll of paper, anchored to a fixed place, and a pendulum or magnet suspended with a marking device above the roll, to record actual earth motion during an earthquake. The scale takes into account the instrument's distance from the epicenter, or the point on the ground that is directly above the earthquake's origin. Richter chose to use the term "magnitude" to describe an earthquake's strength because of his early interest in astronomy; stargazers use the word to describe the brightness of stars. Gutenberg suggested that the scale be logarithmic so an earthquake
Magnitude (astronomy) by astronomers are: The difference between these concepts can be seen by comparing two stars. Betelgeuse (apparent magnitude 0.5, absolute magnitude −5.8) appears slightly dimmer in the sky than Alpha Centauri (apparent magnitude 0.0, absolute magnitude 4.4) even though it emits thousands of times more light, because Betelgeuse is much farther away. Under the modern logarithmic magnitude scale, two objects, one of which is used as a reference or baseline, whose intensities (brightnesses) measured from Earth in units of power per unit area (such as watts per square metre, W m) are and , will have magnitudes and related by