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on Nov 02, 2012

# How long would it take to get to Alpha Centauri?

 Alpha Centauri is the nearest star system to our sun. But, at 4.3 light-years away, getting there would be extremely difficult.

Alpha Centauri is the nearest star system to our sun. But, at 4.3 light-years away, getting there would be extremely difficult. The Alpha Centauri system is much farther away from us than the sun. There’s a lot of empty space between us and this nearest star. If you imagine Earth as a grain of sand, then Alpha Centauri would be over 10 kilometers – or about 6 miles – away.

How far is a light-year?

Of course, in actual fact, Alpha Centauri is trillions of miles away from Earth. Its distance of 4.3 light-years equals 25.6 trillion miles away – nearly 300,000 times the distance from the Earth to the sun.

The Alpha Centauri system. It’s at least a double system, maybe a triple system, but we see it with the eye as just one star. In this image – via MSX/IPAC/NASA – you can almost make out the double nature of Alpha Centauri.

So how could we get to Alpha Centauri? Would a conventional rocket work? Consider the Space Shuttle, which traveled only a few hundred kilometers into space. If Earth were the size of a sand grain, this would be about the width of a hair in contrast to the 10 kilometers to Alpha Centauri. You’d need about 10,000 shuttle main engines in sequence just to build up a decent speed (say, 1/100th light speed). The Space Shuttles weren’t starships. At a maximum speed of about 17,600 mph (about 28,300 kph), it would have taken a Space Shuttle about 165,000 years to reach Alpha Centauri.

The Voyagers’ paths out of the solar system via Wikimedia Commons. Click here to expand image

How about the Voyager spacecraft? These two unmanned space probes – Voyager 1 and Voyager 2 – were launched in 1977. They’re now heading out of the solar system. The Voyagers aren’t aimed toward Alpha Centauri, but if they were, they’d take tens of thousands of years to get there. On the other hand, eventually, the Voyagers will pass other stars. In about 40,000 years, Voyager 1 will drift within 1.6 light-years (9.3 trillion miles) of AC+79 3888, a star in the constellation of Camelopardalis. In some 296,000 years, Voyager 2 will pass 4.3 light-years from Sirius, the brightest star in the sky. Hmm, 4.3 light-years. That’s the distance between us and Alpha Centauri.

The problem with conventional rockets is that, if you’re carrying fuel, you need more fuel in order to carry your fuel to accomplish star-to-star travel.

Other propulsion methods have been discussed, for example, antimatter engines. They work on the principle that, when antimatter and matter meet, they annihilate each other, releasing vast amounts of energy. Scientists have observed bits of antimatter in particle accelerators. But no one knows how to create enough antimatter, or how to store it, for a trip to the stars.

Artist’s concept of a light-sail starship via BBC

How about light sails? This very romantic notion for travel among the stars would rely on thin, lightweight reflective sails, powered by the sun, other stars, or even lasers fired from Earth. You start slow, but accelerate up to light speeds. However, no one imagines a light sail could enable us to travel to Alpha Centauri within a human lifetime.

But all of those propulsion issues are really trivial. Here is the real problem with traveling to Alpha Centauri. Suppose we chose a method of travel, and set out for a trip among the stars. Suppose that, generations from now, our descendants arrived at a planet in the Alpha Centauri system. They might be greeted by brass bands and crowds of earthlings – who left later, but traveled via a more efficient process – and so made the trip in a shorter time.

Starship, via SpaceRip.com

Bottom line: At 4.3 light-years away, the Alpha Centauri system is the nearest star system to our Earth and sun. But getting there would be extremely difficult.

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