Geometric albedo is a measure of the reflective properties of a non-transparent surface, such as a planet or moon. It is the ratio of the amount of light reflected by an object at zero phase angle (directly facing the light source) to the amount of light that would be reflected by a perfectly diffusing disk with the same size and distance from the light source.
Bond albedo is a measure of the total amount of light reflected by an object, taking into account both direct and diffuse reflection. Geometric albedo only considers direct reflection at zero phase angle, while Bond albedo considers all angles of incidence. Therefore, geometric albedo is typically lower than Bond albedo for a given object.
The geometric albedo of an object is affected by its composition, surface texture, and the wavelength of light being reflected. Objects with smooth, highly reflective surfaces tend to have higher geometric albedos, while objects with rough or dark surfaces have lower albedos. Additionally, objects with a higher proportion of light-colored materials, such as ice or snow, will have a higher geometric albedo.
Phase angle is the angle between the observer, the object, and the light source. As the phase angle increases, the amount of direct light reflected by an object decreases, leading to a decrease in geometric albedo. This is because at higher phase angles, more of the object's surface is in shadow, leading to a lower overall amount of light being reflected towards the observer.
Geometric albedo is an important property to measure in planetary science because it can provide information about the composition and surface properties of objects in our solar system. By comparing the geometric albedos of different objects, scientists can gain insights into their surface materials and processes, as well as their overall evolution. Additionally, geometric albedo can be used to calculate the energy balance of planets and moons, which is crucial for understanding their climates and potential habitability.