The diagram above shows you where Alpha Centauri is, with respect to other nearby stars. It’s like that in the Nearest Stars section of the Astronomical Companion, but from a viewpoint that has moved closer and to a different angle so as to get a better look at Alpha Centauri. Included are stars within 12 light-years from the sun. The glows of light representing the stars are millions of times larger than the stars themselves, which would be microscopically small on this scale.

The grid serves to show the equatorial plane, and also the scale, the lines being 4 light-years apart. The slightly thicker line is the vernal equinox direction (the Earth-sun direction at March 20).

Imaginary stalks from the plane to the stars show how far north or south they are. I’ve cropped the picture so that some of the stars are off the top or bottom, but they are obscure stars you may not have heard of, with designations such as Lalande 21185, Luyten 726-8, DX Cancri. Most stars, including most of those near to us, are smaller than our sun – red dwarfs.

The exceptions near to us are Sirius, Procyon, and Alpha Centauri.

Alpha Centauri is the third-brightest star (that is, as seen from our place in space, and not counting the sun). Like the first- and second-brightest – Sirius and Canopus – it is a southern star. Indeed it’s much farther south than either of those, which is why it has no traditional name in our culture (except a rather faux-traditional one, Rigilkent).

The space diagram shows it at a steep southward angle from the sun. This angle (its declination -61°) means it doesn’t peep above the horizon till you go down to the latitude of northern Florida; to see it properly you might go south of Earth’s equator.

Then you would see in your telescope that it is a double star – one of the widest and easiest to “split.” Here is part of my diagram of the pair with which I used to fill a space in Astronomical Calendar 2016:

Because of Proxima Centauri's proximity to Earth, its angular diameter can be measured directly. The star is about one-seventh the actual diameter of the Sun. It has a mass about an eighth of the Sun's mass , and its average density is about 33 times that of the Sun. Although it has a very low average luminosity, Proxima is a flare star that undergoes random dramatic increases in brightness because of magnetic activity. The star's magnetic field is created by convection throughout the stellar body, and the resulting flare activity generates a total X-ray emission similar to that produced by the Sun. The mixing of the fuel at Proxima Centauri's core through convection and its relatively low energy-production rate mean that it will be a main-sequence star for another four trillion years, or nearly 300 times the current age of the universe. 

In 2016, the European Southern Observatory announced the discovery of Proxima b, a planet orbiting the star at a distance of roughly 0.05 AU (7.5 million km) with an orbital period of approximately 11.2 Earth days. Its estimated mass is at least 1.3 times that of the Earth. The equilibrium temperature of Proxima b is estimated to be within the range of where water could exist as liquid on its surface, thus placing it within the habitable zone of Proxima Centauri, although because Proxima Centauri is a red dwarf and a flare star, whether it could support life is disputed. Previous searches for orbiting companions had ruled out the presence of brown dwarfs and supermassive planets. 

That's a daunting distance. But an initiative announced this year aims to send superfast miniature probes to Proxima Centauri, on a journey that would take about 20 years. With the discovery of Proxima b, the founders of that initiative are even more eager to get going.

 

In 2015, NASA's New Horizon probe completed its 3-billion-mile (4.8 billion km) journey to Pluto after traveling for about 9.5 years. The spacecraft traveled at speeds topping 52,000 mph (84,000 km/h). At that rate, it would take New Horizons about 54,400 years to reach Proxima Centauri.

Last month, NASAS Juno probe reached speeds of about 165,000 mph (265,000 km/h) as it entered into orbit around Jupiter. At that rate, a probe could reach Proxima Centauri in about 17,157 years. (It should also be noted that there is currently no feasible way to accelerate a craft large enough to carry humans to those speeds.)

In other words, sending a probe to the nearest star system would not be easy.

The founders of the Breakthrough Starshot initiative want to send wafer-thin probes to Proxima Centauri at very high speeds. The plan calls for equipping these probes with thin sails, which would capture the energy imparted by a powerful Earth-based laser.

This laser would accelerate the probes to 20 percent the speed of light (about 134.12 million mph, or 215.85 million km/h), according to the program scientists. At that rate, the probes could reach Proxima Centauri in 20 to 25 years.

But first, scientists and engineers have to build the apparatus that will launch the tiny probes on their journey. In a news conference today (Aug. 24), Pete Worden, chairman of the Breakthrough Prize Foundation, said that a group of experts had convened earlier this week and discussed plans to build a prototype of the Starshot system. However, he added that the full-scale apparatus is at least 20 years off.

"We certainly hope that, within a generation, we can launch these nanoprobes," Worden said. "And so perhaps 20, 25 years from now, we could begin to launch them, and then they would travel for 25 years to get there."

He added that building the full-scale apparatus would likely cost about the same as building the Large Hadron Collider, the largest particle accelerator in the world; that project is estimated to have cost about $10 billion.

"Over the next decade, we will work with experts here at ESO [the European Southern Observatory] and elsewhere to get as much information as possible about the Proxima Centauri planet … even including whether it might bear life, prior to launching mankind's first probe towards the star," Worden said.

Worden said the Breakthrough Prize Foundation also hopes to "obtain similar data about the other nearby stars, Alpha Centauri A and B." (The two Alpha Centauri stars lie about 4.37 light-years from Earth; some astronomers think Proxima Centauri and the Alpha Centauri stars are part of the same system).

Because of Proxima Centauri's proximity to Earth, its angular diameter can be measured directly. The star is about one-seventh the actual diameter of the Sun. It has a mass about an eighth of the Sun's mass, and its average density is about 33 times that of the Sun. Although it has a very low average luminosity, Proxima is a flare star that undergoes random dramatic increases in brightness because of magnetic activity. The star's magnetic field is created by convection throughout the stellar body, and the resulting flare activity generates a total X-ray emission similar to that produced by the Sun. The mixing of the fuel at Proxima Centauri's core through convection and its relatively low energy-production rate mean that it will be a main-sequence star for another four trillion years,or nearly 300 times the current age of the universe.

 Proxima centauri  might have the right conditions to support life, but it's 4.3 lightyears away and the trip would take conventional rockets thousands of years. 

 Proxima Centauri is a very small red dwarf with a radius of around 60,000 miles (97,000 km), which is around 14% the size of our sun.

 Red dwarfs emit far less energy than larger stars, its luminosity is less than one percent of that of our sun.