 For some things, you simply have to go there to find out how far away it is. For example, how high is the sky? It's not something you can see, so triangulation won't work. To answer this, you need to go there or send something there and report back how far away it is. In the beginning, all we could say for sure about the atmosphere was that clouds were closer to the surface of the Earth than the sun, moon, planets and stars. We knew this because clouds always covered up the surfaces of these objects, never the other way around. Our knowledge in this area didn't really begin until the late 1700s when high-flying balloons came into use. Here's a scientific balloon launch. High-altitude balloons have been used for over 70 years for atmospheric exploration. They fly at altitudes in excess of 32 kilometers above the surface of the Earth for days on end. Even until the 1900s that aircraft, rockets and spacecraft were put to use to travel high into the atmosphere and figure out just how high it went. Turns out that the atmosphere doesn't have an exact top like the lid of a jar. What happens is that the air gets thinner and thinner and eventually merges into and then becomes outer space. Here are the principal layers. The troposphere begins at the surface and extends to around 20 kilometers. This is where we get all of the weather and it is where our passenger jets fly over that weather. The stratosphere extends from the troposphere to about 50 kilometers. The balloons we discussed fly in this area. The mesosphere extends from the stratosphere to around 84 kilometers. It is the layer where most meteors burn up upon entry into the atmosphere. The thermosphere extends up to 386 kilometers and is considered outer space. The air is so rarefied that an individual molecule travels on average about 800 meters between collisions with other molecules. The International Space Station orbits in this layer. Going there is a technique we can repeat for distances throughout our solar system but it won't take us to the stars.