how long is a piece of string?

A space elevator (also called a space bridge, or a beanstalk) is a very long, very strong cable or ribbon. One end is anchored to the Earth's surface and the other end is attached to a satellite orbiting at a height of at least 20,000 miles (36,000 kilometers).

At this height, known as geosynchronous orbit, the satellite orbits the Earth at the same rate as the earth's rotation, so it stays over the same geographical point on the ground. Communications satellites are typically found in geosynchronous orbit.

Oman wrote:

the meaning of life is 42

To measure the solar year length, one can note the interval of time
between two passages of the sun past the same star in the heavens;
(for example, the period between two of its passages past one of the stars shown in figure 20.)

This would be the period of apparent revolution of the sun in the celestial sphere,
or rather
the period of one revolution of the earth in its orbit.
This period is called the sidereal year, because it is fixed by the stars.

In ancient times
as the stars could not be seen near the sun,
-the moon was used as reference.
Before sunset, the distance between the moon and the sun was determined.
After sunset when the star appeared,
-the distance between the star and the moon was measured.
Adjusting for the motion of the moon between the two measurements,
the arc distance between the sun and the star could thus be learned from day to day.