MALE PROFESSOR: That's two stars that rise at the same time, or set at the same time, and navigators could use these pairs of stars as reference points, because they rise or set together only at specific latitudes.

Para27

MALE PROFESSOR: So navigators might see one star pair setting together and, uh, would know how far north or south of the equator they were.

Para28

MALE PROFESSOR: And if they kept on going, and the next night they saw the pairs of stars setting separately, then they would know that they were at a different degree of latitude.

请问老师，这里的how far north的用法是什么？或者说省略了哪些内容？这句话的陈述句应该是什么样的？

 我的猜测： 补全后的句子：How far it is from north or south of the equator they were to thethe equator

陈述句 From north or south of the equator to the equator  is 2000 miles (假设一个数字）