They are all units of measure of length
Explanation:
Length is a scalar quantity representing a distance between two points, and it can be expressed in different units.
The SI units of the length is the metre (m), which is defined as the length of the path travelled by light in vacuum during a time interval of 1/299,792,458 of a second.
A unit which is common used is a multiple of the meter, the kilometre (km) which corresponds to 1000 metres:
1 km = 1000 m
Another unit used in the UK system is the mile (mi), where the conversion factor between miles and metres is
1 mi = 1609.34 m
Finally, these units are not suitable to be used to measure astronomical distances - such as those between stars and galaxies. For this, another unit is used, which is the light-year (ly), which corresponds to the distance travelled by the light in a vacuum in one year, and its conversion factor to the metre is:
Learn more about distance here:
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