(1) UFO stands for “Unidentified Flying Object”. (2) It is any object flying in the sky which cannot be identified by the person who sees it. (3) Sometimes the object is investigated. (4) If people can still not figure out what the object is after an investigation, itis called a UFO. (5) Most scientists think that UFOs are things like meteors, satellites burning up, the planet Venus, flocks of birds, aircraft, car lights, weather balloons, reflections, or tricks. (6) One of the tricks is to make fake photos of flying objects. (7) Another trick is to put balloons with candles in little crates beneath them. (8) The closest star to Earth (other than the Sun) is Alpha Centauri. (9) It’s about 4 lightyears away. (10) Traveling at the speed of light is easy for a photon, but our fastest spacecraft, Voyager, travels at about 40,000 miles an hour. (11) To get there in twenty-five years would require traveling at more than 100 million miles an hour for the entire trip. (12) If you could travel at 100 million miles an hour you could make it to the Sun and back in about an hour and 45 minutes. (13) The spacecraft would have to be built of some mighty fine stuff to endure such speeds for such a length of time. (14) And there would be no repair shops on the way. (15) But the main problem for travel between stars is the fuel, the energy needed to get there. (16) To travel to a star 4 light-years away, we would need 100 times as much energy as our entire planet would use for a year. (17) We couldn’t do it with nuclear fission because our spacecraft would have to carry thousands or millions of nuclear power plants on its wings. (18) Despite the problems that we would face traveling to other star systems or galaxies, it is not impossible. (19) Perhaps there are beings that can travel at very fast speeds and have the technology and the raw materials to build vessels that can travel here from other solar systems. (20) And many people believe that the universe is too big for us to be the only ones out there and the only ones to travel in space. (21) However, it can be said that, when we think about the size and age of the visible universe, the chances of them picking our star and our planet seems pretty slim.