How far away is Alpha Centauri A from Earth?

Saturday, December 19, 2009

Another post related to Avatar today. The journey to Pandora was shown as taking six or seven years, which assumes a ship travelling at somewhere close to light speed (maybe 0.8 c) because don't forget there is also the acceleration when first starting and deceleration before arrival that needs to happen as well. But to truly know just how far away even the closest star to us is we'll have to use the only scale we can imagine: the planets in our Solar System and the farthest we have ever sent a probe. Let's use that to visualize the distance to our nearest stellar companion. Well, companions (there are three stars in the system). But Avatar is based on the largest star, Alpha Centauri A.

First we have an image showing 250 AU. The first dot there (none of these dots are to scale of course) is the Sun, then Mercury, Venus, Earth, Mars, Ceres, Jupiter (in red there, the first one away from the crowd), Saturn, Oranos (my preferred English name for Uranus), Neptune, then Pluto in yellow, and after that there is Haumea, Makemake, and Eris way out on its own. The grey line is the location of Voyager 2, which is thus far the farthest we've ever been able to send a craft out into space.

And now the journey to Alpha Centauri A begins. Don't use the scroll bar on the right! To fully appreciate the distance you have to keep scrolling down with the mouse.

And we are there!

Just joking, we're 8th of the way there. If we're lucky then the recently launched WISE will discover a brown dwarf at about twice or three times this distance. If not, then we'll have to go eight times this distance to reach our first interstellar object. Well, the red dwarf Proxima Centauri is about 0.17 light years closer, which is 10 750 AU or 43 times the first image. But in cosmic terms it's pretty much the same distance.

The good news is that Voyager wasn't sent out to be particularly fast, so it isn't a representative of what we are truly capable of. That is, we're not really trying because there's precious little to see beyond the Solar System. A craft using VASIMR (VASIMR isn't quite flight ready but in a few years it should be) would be able to achieve a velocity of over 100 km/s, which is about 17 days per AU. At that rate it would surpass Voyager 2 in about 4.5 years, not bad since it's taken Voyager 2 a total of 32 years so far to reach its current distance. But at that velocity it would still take 12,900 years or so to reach Alpha Centauri. Voyager 2 would take 72,000 years.


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