# Magnitude

Also called: apparent magnitude, mag, brightness.

The brightness of a sky object on a reversed scale: smaller numbers are brighter, and each step is 2.5× fainter.

The scale goes back to ancient Greece, where the brightest stars were “first magnitude” and the faintest “sixth”. Today it's exact: 5 magnitudes are a factor of 100, so each magnitude is 2.512× fainter. Very bright objects go negative — Sirius is −1.5, Venus up to −4.7, the full Moon −12.7.

Under a dark sky the eye reaches about magnitude 6.5; binoculars about 9.5; an 8-inch telescope about 14. For extended objects, the total magnitude can mislead — see [surface brightness](https://astropilot.space/glossary/surface-brightness).

**In AstroPilot:** Magnitudes appear on every object page and in the sky chart, whose star sizes follow them.

**Related:** [Limiting magnitude](https://astropilot.space/glossary/limiting-magnitude.md), [Surface brightness](https://astropilot.space/glossary/surface-brightness.md), [Light grasp](https://astropilot.space/glossary/light-grasp.md), [Extinction](https://astropilot.space/glossary/extinction.md)

From the AstroPilot astronomy glossary: https://astropilot.space/glossary/magnitude