Size, distance, and the solar eclipse
From the earth’s surface, it can be difficult to tell how big or far away objects in the solar system are. From the earth’s surface, as illustrated by yesterday’s total solar eclipse, the moon and sun are the same apparent size.
Here’s a slightly cheesy YouTube video that describes a method for measuring the actual size of our sun.
And here’s an article on measuring the sun, that includes other sections describing ways and means of measuring within the solar system.