system
Given the following post, respond as if you're commenting on Reddit:
human
How were we able to measure how big the sun is?

I was just wondering because I've heard throughout my schoolyears the size of the sun and the distance, but we are not able to get close to it. How do we know?
gpt
Combination of two methods for direct observation:

1. Parallax: gives you the distance to an object. Works by making angular measurements of the distant object from two positions whose location is precisely known, and then using trigonometry to determine the distance. If you know two angles and a the length of one side of a triangle, you can figure out all the remaining dimensions.

2. Apparent width: Using the appropriate filter (welding goggles work well) one can measure how wide an object appears at a certain distance from ones eye. Once you know the distance to the object, you can determine how wide it really is by taking the ratio of distance and widths. (real width) = (measured width) x (distance to object - distance to measured width location) / (distance to measured width location). Of course in reality, the sun does not have a defined surface or edge, but this method will get you some idea of the scale of it.