How do astromers know the distance of a planet/sun/galaxy?
They use trigonometry. They figure its location in the sky, then six months later they find it again. We now the distance from Earth to Sun and to Earth again across the orbit due to lots of different types of measurements….some with spacecraft. Next, the scientists make a “triangle”…one corner is the Earth’s location six months ago…one corner is its location today, and one corner is the object that we want to measure the distance to. After this…its easy geometry. We find the angle of the line between Earth’s two locations to the line to the object from each location, giving us two of the three angles of the triangle…add together, subtract from 180, and that is the measure of the third angle of the triangle. Now we know the length of one side of the triangle and all three corners…now a little algebra will tell us the length of the other two sides, allowing us to know the distance to the object. Small errors are ok…since we measure in units of 6 trillion miles. For objects
