Density measurement is used to specify and describe a pure substance, but also determines concentrations of binary mixtures and therefore gives information about the composition of mixtures. It is, for example, useful during quality control or helps determine the filling volume during the bottling of a product.

Density of mass

• Density, mass per unit volume.
• Area density or surface density, mass over a (two-dimensional) area.
• Linear density, mass over a (one-dimensional) line.
• Relative density or specific gravity, a measure of density in comparison to the density of something else.

Osmium

second

The behavior of light can be seen in the behavior of waves and photons, the basic unit of light. A wavelength (which varies inversely with frequency ) manifests itself as color, while wave amplitude is perceived as luminous intensity or brightness; it is measured by the standard unit of a candela.

The lux (symbol: lx) is the SI derived unit of illuminance, measuring luminous flux per unit area. It is equal to one lumen per square metre. In photometry, this is used as a measure of the intensity, as perceived by the human eye, of light that hits or passes through a surface.

The SI unit of light year is kilometre.

63,241 astronomical units

As defined by the International Astronomical Union (IAU), a light-year is the distance that light travels in vacuum in one Julian year (365.25 days). Because it includes the word “year”, the term light-year is sometimes misinterpreted as a unit of time….

about 6 trillion miles