Isophote

ellipsoid with isophotes (red)

In geometry, an isophote is a curve on an illuminated surface that connects points of equal brightness. One supposes that the illumination is done by parallel light and the brightness b is measured by the following scalar product:

where is the unit normal vector of the surface at point P and the unit vector of the light's direction. If b(P) = 0, i.e. the light is perpendicular to the surface normal, then point P is a point of the surface silhouette observed in direction Brightness 1 means that the light vector is perpendicular to the surface. A plane has no isophotes, because every point has the same brightness.

In astronomy, an isophote is a curve on a photo connecting points of equal brightness. [1]

  1. ^ J. Binney, M. Merrifield: Galactic Astronomy, Princeton University Press, 1998, ISBN 0-691-00402-1, p. 178.