Light trip

      The light propagates at a speed about 3.10^6 m/s, beside the time. So, all that travels in this speed isn't affected by the time.

      There is a popular unit of measurement in astronomic metier, called light-years, this unit is about the distance which the light travel for one year. The name makes feel like it measure time, but it really measure distance. The fact of the light has a supreme velocity and the universe elements are arranged so far apart from each other makes any phenomena wich feels like weird at first time.

      Initially, suppose that our sun explode, we only will know after about 8 minutes, because the light takes 8 minutes to travel from the Sun till here, awesome, no?

      The same thing is possible to be observed in a larger scale: suppose that there is a planet arranged at 80 millions light-years to Earth, the light will delay 80 millions years to arrive over there. So, the light that the planet is "seeing" now is the image of Earth had 80 millions years before. And if a dweller of this planet looks by a telescope he will watch the Earth like it was 80 millions years ago, he would see dinosaurs.

      Knowing all this, we can think that maybe this is the reason to the Earth hadn't be visited by aliens, already then planets most nearby are so far then just a short information of Earth come for they, can delay to they see a civilization in progress and so the same is intersting to visit, and even this really happen the aliens would have  to travel in the same velocity of the light and have their life expectancy too larger, to survive  to this travels.

      Many speculations can be created on this thinking line...  Will we travel to explore other planets on day? Or they will travel to explore us first? Nobody knows.