[annalex]

The speed of light through time or space can be represented by a right triangle. One axis is the speed of light through time, the other is through space.

This part I don't understand. Let us forget about two of the three spatial dimensions. Then you have the continuum (X,T). Two axes, the observer in the center (0,0). A particle of light is at (x,t). Its speed is dx/dt, and that is constant. The triangle is (0,0) - (0,t) - (x,t). Where is speed through time and speed through space?

[annalex]

Ah, wait. I got it. dx/dt is speed through space. dt/dx (time elapsing per mile of traveled space) is speed through time. Both are constant.

So where are we going from here?