This is a list of galaxies sorted by surface brightness. Surface brightness is a measure of how bright a diffuse object like a galaxy or nebula appears over its extended surface. The brightness over the entire galaxy is called apparent magnitude.
The surface brightness is calculated via . Where is surface brightness, is total magnitude, and is the total area in square arcseconds. Area is calculated using the formula for an ellipse; , where is the semi-major axis and is the semi-minor axis. Each axis is half of the dimension, because each dimension is the entire length/height but the axis is only the length/height to the centre, this combined with the symmetry of an ellipse means that half the dimension is the axis.
Combining this with the original formula we get: , which simplifies to .