Base unit (measurement) aspects of the world, such as time, distance, velocity, mass, temperature, energy, and weight, and "units" are used to describe their magnitude or quantity. Many of these quantities are related to each other by various physical laws, and as a result the units of a quantities can be generally be expressed as a product of powers of other units; for example, momentum is mass multiplied by velocity, while velocity is measured in distance divided by time. These relationships are discussed in dimensional analysis. Those that can be expressed in this fashion in terms of the base units are called .
Earth mass value) in the Schiehallion experiment in the 1770s, and within 1% of the modern value in the Cavendish experiment of 1798. The mass of Earth is estimated to be: which can be expressed in terms of solar mass as: The ratio of Earth mass to lunar mass has been measured to great accuracy. The current best estimate is: The "G" product for the Earth is called the geocentric gravitational constant and equals It is determined using laser ranging data from Earth-orbiting satellites, such as LAGEOS-1. The "G" product can also be calculated by observing the motion of the Moon or