Seismic magnitude scales indirectly and incompletely reflect the force of an earthquake, involve other factors, and are generally limited in some respect of magnitude, focal depth, or distance. The "moment magnitude scale" – Mw or M – developed by and , is based on an earthquake's "seismic moment", M, a measure of how much work an earthquake does in sliding one patch of rock past another patch of rock. Seismic moment is measured in Newton-meters (Nm or Nm) in the SI system of measurement, or dyne-centimeters (dyn-cm) in the older CGS system. In the simplest case the moment can be calculated knowing only
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