allowing for much lower supersaturation rates as compared to ice clouds), the relaxation times will be very low (seconds to minutes). In ice clouds the concentrations are lower (just a few per liter) and the temperatures are colder (very high supersaturation rates) and so the relaxation times can be as long as several hours. Relaxation time is given as where: D = diffusion coefficient [m2/s] N = concentration (of ice crystals or water droplets) [m−3] R = mean radius of particles [m] K = capacitance [unitless]. In astronomy In astronomy, relaxation time relates to clusters of gravitationally interacting bodies, for instance, stars in a galaxy. The relaxation time is a measure of the time it takes for one object in the system (the "test star") to be significantly perturbed by other objects in the system (the "field stars"). It is most commonly defined as the time for the test star's velocity to change by of order itself. Suppose that the test star has velocity v. As the star moves along its orbit, its motion will be randomly perturbed by the gravitational field of nearby stars. The relaxation time can be shown to be where ρ is the mean density, m is the test-star mass, σ is the 1d velocity dispersion of the field stars, and is the Coulomb logarithm. Various events occur on timescales relating to the relaxation time, including core collapse, energy equipartition, and formation of a Bahcall-Wolf cusp around a supermassive black hole. See also Relaxation oscillator Time constant References Time in physics Time in astronomy Celestial mechanics fr:Constante de temps