It would take light about 4.22 years to travel from earth to Alpha Centauri, the closest neighboring star system. Human travelers in any conceivable spacecraft would take considerably longer. A light-year, the distance light travels in a year, is actually a measure of distance in the unimaginably vast universe.
Light travels about 984,000,000 feet in a second. This works out to about 5.88 trillion miles in a year. The distance to Alpha Centauri, then, is approximately 4.22 times 6 trillion. Therefore, the distance to Alpha Centauri is something like 25,000,000,000,000 miles.
This distance is inaccurate because it was arrived at by using approximations. Another reason for its imprecision is because Alpha Centauri is not a single star but a star system. It is composed of stars in motion, spread out across millions of miles of space.
Alpha Centauri is brilliant, appearing as the third-brightest star in the night sky. It hangs in the Southern Hemisphere sky, where it was invisible to star-charting Greek astronomers until their Hellenistic civilization spread as far south as Egypt. An arm of the Southern Cross constellation seems to point at Alpha Centauri, where it is part of the constellation Centaurus, the Centaur. Alpha Centauri is traditionally called Toliman or Rigel Kentaurus, the Heel of the Centaur, but it is not a star.
The Alpha Centauri star system is composed of two or three stars and perhaps of planets, as well. One star of Alpha Centauri is quite like the sun, but slightly larger. One is smaller while more orange and about half as luminous, or bright, as the sun. These two stars rotate around a common center of gravity, closely, by astronomical standards. The third star is a red dwarf, its membership in the system, uncertain.
Alpha Centauri A, the brightest star in the system, resembles the sun in several ways. Its size and color are similar to the sun, but it is about 1.5 times as bright. If this star system has rocky, earth-like planets, they could well orbit close to Alpha Centauri A or B. Alpha Centauri B is a smaller and more orange star. Alpha Centauri A and B orbit each other at a distance of about 2.3 billion miles. It takes just under 80 years for them to complete an orbit.
The other nearby star, Proxima Centauri, is a red dwarf. It may not be part of the Alpha Centauri star system. The question is whether the star is gravitationally bound to the system and truly a part of it or is only a visitor that will move on after a few million years. If it is bound, it moves in an enormous orbit, taking perhaps a million years to go all the way around.
It is a dim star, about 7,000 times dimmer than the sun, but is also a flare star, one that can experience sudden brief dramatic increases in brightness. At about 4.22 light years away, Proxima Centauri is the closest star to our sun.