As the earth revolves around the sun, distant objects can be seen from different locations. This idea can be used to measure the distance between earth and nearby stars and is called stellar parallax. To see how this process works, consider the simplified scenario below.
A distance object is observed on earth from location 1 and again six months later at location 2. The angle at both location 1 and 2 is 89.9 degrees. How many astronomical units is the distant object from location 1?