Lorenz-factor has remarkable influence at speeds near to light, but formula itself has no limits. So, time dilation occurs also with slow speeds. From my point of view (an observer), Venus and Mars have different speeds which means different time dilation and this means different speed of light. So, both planets are sending a ray of light towards me with different speeds. - Which is not possible. If time dilation would be an imaginary phenomenon, there wouldn't be any problems. But when two worlds with different time dilation meets each others, there is a problem. What explains this?