Red line is the speed of light. 300,000 km/s if I remember correctly. Slope is 0 (or 0 degrees). Green line is no movement. Don't know what the slope would be (it's made up in my diagram, for all I know it could be the blue line). Does that sorta clear things up? "x" is speed, f(x) is the slope or angle of the line. We would be somewhere between the green line and the red line because we are moving, but no where near the speed of light. I'm not taking gravity into consideration though, which is a factor, so if needed just assume gravity is the same in all cases.