Alpha Centauri

Alpha Centauri is the closest star system to our Sun. It is actually a triple star system, with Alpha Centauri A, a G2V star much like our Sun, Alpha Centauri B, a slightly smaller and cooler K1V star, and Proxima Centauri (also Alpha Centauri C), an M6V red dwarf. Proxima Centauri is named thus, because is the closest star to our Sun.


Alpha Centauri is approximately 4.34 light years away, and as shown above, the largest of the stars is very similar to the Sun. This stellar system is important and will be the first star system humanity will ever visit when we are finally able to leave our own Solar System. Right now, it would take about 81,000 years with our fastest spacecraft technology to reach the star system.


Once we get to Alpha Centauri, we will be able to see if it has planets similar to ours and if the planetary system would be recognizable to us. We would want to see if there were any Earth-like planets and if there could be life on them. Just like the Moon should be our first logical step in colonizing the Solar System, Alpha Centauri is the first logical step in exploring our galaxy.

Parallax

How do astronomers measure distances to stars? One way is to measure what is called the parallax angle of the star which compares the position of the star to more distant, background stars. Parallax is a part of astronomy called astrometry which is the measure of stellar distances and motions.

• p is the parallax angle measured in arcseconds (1 arcsecond is 1/3600 of a degree)
• r is the distance from the Earth to the Sun (astronomical unit)
• d is the distance from the Sun to the star (in essence from the Earth to the star since r<<

In trigonometry, p is actually the arctan of r/d, but for small angles, tan(p) is approximately p. Astronomers then define a unit of measure called a parsec to make calculations easier.

• One parsec is the distance a star would have to be from the Sun to create a parallax angle of 1 arcsecond (1") as seen from Earth (r = 1 AU)

Notice that the parallax angle is only one-half of the total angle created for the star's position in January and June.

What's nice about this equation, is it works for any distance r as long as r is measured in AU. There was talk about placing a space probe near Jupiter's orbit to create a much larger baseline. Remember, that r for Jupiter is approximately 5.2 AU which means the angle p would be 5.2 times larger than at Earth. Larger angle are obviously easier to measure than small angles.

The closest star to the Sun (Earth) is Proxima Centauri. Its parallax angle is approximately 0.75" which means it is about 1.3 parsecs from Earth. All other stars have a larger distance, so they have much smaller parallax angles, which is why it would be better to measure parallax farther out in the Solar System.