Magnitude refers to the size or extent of something, and there are several uses of the term in different scientific fields. In physics, it refers to the quantity of a measurement, whereas it refers to the brightness of stars in astronomy. In geology, magnitude indicates the strength of an earthquake.
Magnitude is often used in physics and mathematics in reference to vectors. Vectors are figures that have both quantity and direction. The quantity portion of a vector is called its magnitude. For example, a car traveling 50 mph east has a magnitude of 50 and a direction of east.
In astronomy, magnitude refers to the relative brightness of a celestial object as seen from a specific point. Objects with higher magnitudes are dimmer and harder to see. The sun has a magnitude of -26 as seen from Earth.
Magnitude in geology refers specifically to the amount of movement produced by an earthquake. Magnitude scales for earthquakes are logarithmic, meaning that each point on the scale is 10 times larger than the one below it.