What do the words "isophotal" and "photometric" mean? I can't find any definitions.
Isophotal refers to the equal brightness contours or lines on a two-dimensional image, while photometric refers to the measurement of the light intensity or brightness of an object.
The main difference is that isophotal measurements are qualitative, representing the perceived brightness of an object, while photometric measurements are quantitative and can be used to determine the exact brightness of an object.
Isophotal and photometric measurements are used to study the brightness and distribution of light from celestial objects, such as stars and galaxies. This information can provide insights into the physical properties and evolution of these objects.
Isophotal measurements can be affected by factors such as atmospheric conditions, while photometric measurements can be affected by factors such as the distance of the object, its color, and any intervening dust or gas that may absorb or scatter light.
Some common techniques include aperture photometry, which involves measuring the light within a specific area around the object, and isophotal fitting, which involves fitting a mathematical model to the isophotal contours of an object to determine its brightness profile.