Distance is a common term that we relate to in our day to day lives. As such, distance is nothing but a numerical measurement of how far objects are placed from each other. The concept is studied in many instances. For example, in physics distance usually refers to a physical length or an arithmetic calculation based on some criteria whereas distance in mathematics is referred to the function or metric which is used for the generalization of the concept of physical distance. Having said that, here we will understand a bit more about the concepts and mainly look at the unit of distance.

## SI Unit of Distance

Generally, if we consider shorter distances, the SI unit of distance is a meter. Interestingly, using this as the base unit and some equations, many other derived units or quantities are formed like volume, area, acceleration and speed. Likewise, the most basic unit of distance is also centimetre (cm).

### Commonly Used Distance Units

When we talk about or when we have to measure longer distances they are other units used. Some of them include;

- The solar radius of 7 × 1010cm.
- The Astronomical Unit (AU) which is the mean distance from the Earth to the Sun, 1.496 × 1013cm, or about 93 million miles.
- A light-year (ly), the distance travelled by light in one year, or 9.46 × 1017cm. More significantly, one light-year is equal to 9,500,000,000,000 kilometers.
- The parsec (pc), the distance at which an object has a parallactic shift of 1 second of arc, or more accurately 3.1 × 1018cm. Usually, there is 3.26 ly in a pc and 206,265 AU in a pc.

Other common units include Angstroms, nanometers, microns, millimetres, miles, kilometre.

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