The apparent magnitude (m) of a celestial object is a number that measures its brightness as seen by an observer on Earth. The brighter an object appears, the lower its magnitude value (i.e. inverse relation). The Sun, at apparent magnitude of −27, is the brightest object in the sky.
Magnitude is a logarithmic measure. It is measured in a specific wavelength or passband, usually in optical or near-infrared wavelengths. A full moon is −13 magnitude and the brightest planet Venus measures −5. The brightest man-made objects, Iridium flares, are ranked at −9 and the International Space Station measures −6.