The closest star to the Earth is the Sun, a yellow dwarf star with a mean distance of 93 million miles from Earth. That being said, what I think most people really mean from this question is what is the closest star to the Earth outside of the Solar System. The quick answer to that is Proxima Centauri, one of the three stars of the Alpha Centauri star system and the closest one to Earth by a small margin. Let’s take a look at this in more detail.
Alpha Centauri is the closest star system to Earth, 4.37 light years away, and of course contains the closest star(besides the Sun) to Earth, Proxima Centauri, also known as Alpha Centauri C, which is about 4.24 light years away.
Alpha Centauri is a triple star system consisting of Alpha Centauri A, also known as Rigil Kentaurus, Alpha Centauri B, also known as Toliman, and Alpha Centauri C, with the official name of Proxima Centauri. To the naked eye, the Alpha Centauri star system appears in the night sky as a single star with an apparent magnitude of -.27, which makes it the 3rd brightest star visible in the night sky behind only Sirius and Canopus – Sirius is the brightest star overall and Canopus is the brightest star in the southern hemisphere(2nd brightest overall).
Rigil Kentaurus(Alpha Centauri A) and Toliman(Alpha Centauri B) are both yellow dwarf stars which are very similar to the Sun. Rigil Kentaurus has a mass of about 1.1 times that of the Sun and a luminosity(total emission of electromagnetic radiation) about 1.5 times as much. Toliman is slightly smaller with .91 times the mass and only .45 times the luminosity of the Sun. These two stars orbit each other around a common center of gravity making a complete revolution approximately every 79.9 years. Their elliptical orbit is highly eccentric which means that the distance between the two can vary from roughly 3.31 billion miles to 1.04 billion miles.
As mentioned before, Proxima Centauri is the closest star to Earth besides our Sun, Rigil Kentaurus is the second closest, and Toliman is the third closest.
Proxima Centauri is a low mass red dwarf star about 4.24 light years from Earth and can be seen in the constellation Centaurus in the southern hemisphere or in very low latitudes(20 degrees or less) in the northern hemisphere. In other words, most countries in the northern hemisphere will not be able to see the Alpha Centauri star system, you need to be fairly close to the equator, 20 degrees or less to see it since it is mainly seen in the southern hemisphere.
Robert Thorburn Ayton Innes, a Scottish astronomer, discovered Proxima Centauri in 1915. For many years, because of it’s greater distance from Alpha Centauri A and B, it was thought that Proxima Centauri might not actually be a part of the Alpha Centauri system, but rather a nearby star to Alpha Centauri A and B outside their gravitational pull. Eventually, after intense observations and more in-depth
Proxima Centauri is the third star in the Alpha Centauri system with a separation from Alpha Centauri A and B of about 1.205 trillion miles, about 12950 astronomical units(an astronomical unit is equal to the mean distance of the Earth from the Sun, about 93 million miles). Unlike Alpha Centauri A and B, Proxima Centauri is much to faint to be seen with the naked eye since it has an apparent magnitude of 11.13; it can, however, be seen with a reasonably good telescope.
As previously mentioned, Proxima Centauri is a low-mass star, with a mass only about one-eighth(12.3 percent) that of the Sun and a diameter one-seventh that of the Sun(one and one-half times that of Jupiter), thus it’s volumetric mass density(mass per unit volume) is about 33 times that of our Sun. Although having a very low average luminosity, only about .17 percent that of the Sun, Proxima Centauri is considered to be what is known as a flare star – this is a star which has significant variability in brightness meaning that there can be somewhat dramatic increases in brightness for short periods of time. In the case of Proxima Centauri, this is believed to be caused by flares similar to the solar flares that we see on the Sun, which are in turn caused by magnetic activity generated by convection currents occurring throughout the body of the star. The somewhat low energy production of Proxima Centauri means that it may be able to maintain it’s luminosity for another 3 or 4 trillion years, hundreds of times the current estimated age of the universe!
Proxima Centauri B
Proxima Centauri B, also known as Proxima B, is an exoplanet orbiting in the habitable zone of the red dwarf star Proxima Centauri about 4.24 light years from Earth, making it the closest known exoplanet. It was discovered in 2016 by the European Southern Observatory and has been determined to be orbiting Proxima Centauri at a mean distance of 4.66 million miles about every 11.2 Earth days(the year of Proxima Centauri B is only 11.2 days compared to 365 days for the Earth!) with a mass roughly 1.3 times that of Earth. Since Proxima Centauri has a much lower energy production and luminosity than the Sun, it’s habitable zone is much closer to the star compared to the Earth from our Sun – 4.66 million miles versus 93 million miles.
Proxima Centauri B is believed to have a temperature range in this habitable zone such that water could exist in a liquid state on its surface. The presence of liquid water enhances the possibility of life, although this is disputed because of the fact that Proxima Centauri B is a flare star which could conceivably cause too much variability in temperatures – this could be detrimental to the development of life, although it is not really known at this time. There is certainly a possibility of some type of alien life on Proxima Centauri B!
Proxima Centauri – Future Exploration
There has been much speculation about traveling to the stars and how it might be done. Since Proxima Centauri is the closest star to our Solar System, it has already been proposed as a destination for interstellar travel.
With current conventional(chemical) propulsion technology it could take tens of thousands of years for a space probe to reach Proxima Centauri. An example of this we can see right now is the Voyager 1 space probe, the furthest from Earth, which is now traveling at slightly over 38000 miles per hour. At this velocity if it were traveling in the direction of Proxima Centauri(which it is not) it would reach the star in approximately 73800 years. By then who knows if there would even be any humans around to see it. Clearly, a superior method of propulsion must be developed.
Some type of nuclear propulsion system could cut the travel time down to a century or two. One interesting project which is in the very earliest planning stages right now is called Breakthrough Starshot, which has as its goal reaching the Alpha Centauri system by the year 2050. This would be done by using micro space probes, miniature light sailing ships called StarChips, which would be propelled by Earth-based lasers reaching about 20 percent of the speed of light. These micro space probes would reach the Alpha Centauri system in a little over 20 years, making a flyby of Proxima Centauri and exploring it’s exoplanet Proxima Centauri B in detail. Photos would be taken and its atmosphere would be analyzed in detail. This data would then be transmitted back to Earth and would be received in about 4.24 years because of the light speed barrier.
And perhaps one day humans will make their first interstellar journey to Proxima Centauri, maybe using propulsion technologies that we can scarcely imagine today. Who knows, maybe we’ll even have warp drive or something similar by then!