Milky Way Galaxy

Figure 1. The center of the Milky Way Galaxy.

future space travelers

Figure 2. Humans may eventually explore Earth-like worlds around other stars.

With your eyes alone, away from the glare of street lights, you can see about 2,000 stars on a clear night. Binoculars or a small telescope will show you many more. In fact, our sun belongs to a huge, spiral-shaped star city, or galaxy, of about 200 billion stars. What is more, astronomers estimate that there may be about 100 billion galaxies. That makes a grand total, for the whole universe, of about 10 billion trillion stars – enough to keep even the most ambitious space explorers busy for a long time to come. But of that great mass of stars, which ones will the people of Earth choose to visit?


In Search of Alien Worlds

Stars come in an immense variety. There are giants and dwarfs, hot stars and cool stars, and stars along or with companions. Stars also differ greatly in the amount of light they give off. In fact, the brightest stars you can see in the sky may not be the closest. For example, the nearest star to the Sun, Proxima Centauri, is a very dim kind of star called a red dwarf. You would need a powerful telescope to be able to see it. On the other hand, the brilliant orange star Betelgeuse, in the constellation, or star pattern, of Orion, is more than 300 light-year away. It is a supergiant, so large that if it were put in place of the Sun, it would cover the orbits of Mercury, Venus, Earth, and Mars.


Other bright stars are among our neighbors. Sirius, for example, the brightest star in the sky, is slightly more than eight light-years away from Earth. Although it is really much fainter than Betelgeuse, it appears to be brighter because it is so much closer to us. Alpha Centauri, another brilliant star, can be seen only from the Southern Hemisphere. It belongs to the same star system as Proxima Centauri, and lies at roughly the same distance.


The first stars to be visited, either by robot probes or astronauts aboard starships, will be the ones that are fairly nearby. But even within 20 light-years of the Sun, there is quite a selection of stars to choose from. A number of red dwarfs, or two Sun-like stars, and Sirius are among the possible choices.


Decisions about future missions to the stars will also be based on whether or not a star has planets. In addition to providing a place for spacecraft to land, some planets of other stars may support alien forms of life. At the very least, there may be worlds that would be suitable for human beings to colonize or explore.


Astronomers have already discovered several hundred planets going around other stars and many more are likely to be detected in years to come. Future space travelers may especially choose to visit a star that closely resembles the Sun. A planet circling such a star at about the distance of Earth from the Sun might be an ideal place for humans to land on and build colonies. Nearby Sun-like stars include Alpha Centauri (4.3 light-years away), Epsilon Eridani (10.8 light-years away), and Tau Ceti (11.6 light-years away).


Why Fly to the Stars?

However it is achieved, crossing trillions and trillions of miles of space to reach other stars will involve a huge effort. It will be risky, time-consuming, and expensive. So, why should we bother? Wouldn't it make more sense to stay here on Earth where conditions are just right for us, and we have everything we need?


Many arguments have been put forward in support of space travel. Mining raw materials on other worlds, relieving the world's population problem, learning more about the universe – these are just some of the reasons people have suggested. But the most important reason of all has no practical value. It is simply that human beings like to explore (see Figure 2).


If there is somewhere that no one has ever seen or traveled to, sooner or later men and women will choose to go there. It is the same urge that has driven explorers to face great dangers in their quest to reach the frozen poles, penetrate the steamy, tropical jungles, or climb the highest mountains. Now we are running out of new frontiers to explore on Earth. We have begun to look, first to the other worlds of our solar system, and then to the distant worlds of other stars.


No one can say when the first robot probe will leave on its journey to Barnard's Star, or Alpha Centauri, or another stellar neighbor of the Sun. But it will happen. And, in time, humans will follow and cross the vast interstellar spaces themselves.


To begin with, they may simply stop for a while to explore the strange, new worlds of other stars. But later, they will build bases and, eventually, great cities on some of those alien planets. Over many years, the human race will spread from star to star, moving ever more deeply into the uncharted reaches of the Galaxy. We may even encounter other races of beings, perhaps more advanced than ourselves. If we can solve the difficult problems we face on our planet today, we have a tremendous future ahead of us in the great, unexplored universe.


Could you, then, ever travel to the stars? We have seen that the answer is definitely yes. Daedalus-like probes could probably be constructed and launched by late in the twenty-first century. Faster, human-carrying starships, such as the interstellar ramjet, may not be built until much later. Today, it is too early to tell if we will ever be able to hop from star to star, or from galaxy to galaxy, with the help of black hole "subways." But the fact that we can already talk about such an incredible way to travel is encouraging.


The stars challenge us every night with their beauty and mystery. Someday we shall accept that challenge.