Hi, in the past we could just travel and see some cities around or at last from one country to the other and for further travels we might not be able to back to the first t was risky. But by developments in science and technology it is possible to travel to where we want on earth. But yet there are some unavailable places in the universe. We are here on the earth and the earth with some other planets are n the solar system. Do you know how many planets are there in the solar system? Let’s watch the video to know it.