What are lightyears and why do scientists use them?

Light years are the distance is takes light to travel in a year. Scientist may use light years to measure the distance of how far away a star is, or other celestial objects.

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Most objects in space are so far away, that using a relatively small unit of distance, such as an astronomical unit, is not practical. Instead, astronomers measure distances to objects which are outside our solar system in light-years.

Source: coolcosmos.ipac.caltech.edu/cosmic_classroom/cosmic_reference/distance.html

a social contract.

"a social contract is an agreement between citizens and their leader where the citizens give up certain freedoms in exchange for protection. the constitution of the united states is an example of a social contract."

answer: ensure protection from communism

explanation:

the north atlantic treaty was largely dormant until the korean war initiated the establishment of nato to implement it, by means of an integrated military structure: this included the formation of supreme headquarters allied powers europe in 1951, which adopted the western union's military structures and plans.