In science we use very big and very small numbers. Scientists have developed units of measurement which make the numbers easier to manage. For example, instead of saying that the Sun is 93 million miles from the Earth, it is easier to say the Sun is one from the Earth. In science that is the unit of measure for the distance from the Sun to the Earth.

Astronomical Unit

Explanation:

The astronomical unit is a unit of length, roughly the distance from Earth to the Sun and equal to about 150 million kilometres (93 million miles). However, that distance varies as Earth orbits the Sun, from a maximum (aphelion) to a minimum (perihelion) and back again once a year.

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figureit out

explanation:

because scientists need to know the stars so they understand space