An isophote is a contour of equal surface brightness in an astronomical image. Deviations from fitted ellipses encode additional information about a galaxy's projected stellar structure.
Writing an isophote's radial residual about its fitted ellipse as , positive extends the major and minor axes and gives a pointed, disky shape; negative extends diagonal directions and gives a boxy shape. The sign stated here is for radial residuals, not an unconverted brightness residual. Massive slowly rotating elliptical galaxies commonly have boxy isophotes, while embedded rotating disks commonly make lower-mass elliptical galaxies disky.
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An isophote is a line or contour on a diagram or image that connects points of equal brightness or intensity. In the context of astronomical imaging and other fields such as photography and remote sensing, isophotes are used to represent the distribution of light intensity across a surface, like that of a galaxy, star, or other celestial objects. In astronomy, isophotes can help in studying the spatial distribution of stars within galaxies, the morphology of galaxies, and the characteristics of nebulae.