Magnitude

From South Dublin Astronomical Society

Apparent Magnitude is the term astronomers use to indicate the brightness of objects as seen from Earth.

The faintest star that can bee seen with the naked eye is about 6.0 from a dark sky. Brighter stars have a lower number, and very bright objects such as bright planets often have a magnitude below 0.

The scale used is logarithmic, so a star of magnitude 2 is about 2.5 times dimmer than a star of magnitude 1.

Apparent magnitude is taken as being all the light from an object when focussed on a point, however for diffuse objects such as galaxies the magnitude is spread out over an area, causing the object to appear dimmer than the magnitude in a star map may indicate.

The other magnitude scale used by Astronomers is Absolute Magnitude. Un like Apparent Magnitude, which is the brightness we see, Absolute magnitude is a measure of how bright the object actually is. It is defined as the Magnitude the star would have at a distance of 10 parsecs (32.62 light years).