Easy astrophysics equations

The focal ratio or f/stop is considered as the “speed” of the optics in any telescope or device which uses a lens mechanism.
This measurement is computed by dividing the focal length by the lens’ aperture.
You have a telescope whose lens aperture is 102 millimeters and focal length of 1000 millimeters.

But a more general and generally applicable equation of state is often that of an adiabatic equation of state.
As you might have encountered before in a physics class
An adiabatic process is one that occurs in a system without any exchange of heat with its environment.