Feet
Kilometers
It would be millimetres.
A kilometre is quite a long unit of measurement. For this reason you would use it to measure large things on earth. For example:The distance between citiesThe length of a coastlineHow far a train journey is
To measure the distance of stars you have to measure by light years.
Kilometres or miles.
Light year is used to measure the stellar distances whereas miles and km is used to measure distance on Earth.
Kilometers
No. A light year measures such large distances that it would be highly impractical to measure anything on Earth. The light year is used to measure distance in space beyond the solar system.
Distances on the road, or very large parcels of land. Probably the distance from the earth to the moon.
I would use million miles to measure the distance from the Earth to the Sun. The average distance is about 93 million miles.
Light year is used to measure the stellar distances whereas miles and km is used to measure distance on Earth.
It would be feet
Because of the unwieldy large numbers that would otherwise be required.A Parsec is the distance from the Sun to Earth, and a light year is the distance that light would travel in a year.
An AU is much larger than any distance on Earth. Earth's equatorial circumference is about 0.00027 . So measuring distances on Earth in AU would be like measuring the sizes of small animals in miles.
Astronomers measure the parallax angle of a planet or star to determine its distance from Earth. By observing the apparent shift in position of the object against the background stars as the Earth orbits the Sun, astronomers can calculate the angle and use it to estimate the object's distance.
You would measure the distance of the door with meters because liters measure volume not length.
Light years aren't the best, since it is only about 0.000624 light years away. Saying that the distance is 39 AU would be better. On the other hand, it's a much better unit than saying the distance is 3,229,510,630,000 fathoms.