Since the magnitude of the vector is equal to the magnitude of velocity, velocity of the 2 cm vector represents a velocity of $10\times 2= 20 \: km/h$.
A nebula is gas, dust, and other things that form and form some sort of clould like thing. It also looks cool because of the colors it produces. I'm sure you could do a web search to find more about it, I don't take astronomy hahaha
