How big is Distance from Proxima Centauri to Alpha Centauri A?

Proxima Centauri, a small red star, is about 1.8 trillion kilometers from Alpha Centauri A, the brighter of the two stars it orbits. That is about 12,000 astronomical units, where one astronomical unit is the average distance from Earth to the Sun. It is also about 0.19 light-years, where a light-year is the distance light travels in a year, about 9.46 trillion kilometers. It is the distance between the stars today, which changes very slowly as Proxima moves along its orbit.

Distance

Alpha Centauri A and B are a pair of stars much like the Sun that circle each other every 80 years. They stay between about 11 and 35 astronomical units apart, far closer to each other than to Proxima. Proxima is a red dwarf, a star much smaller and cooler than the Sun. It is almost exactly as far from A as from B.

The distance is worked out from where each star appears in the sky and how far each is from the Sun. Proxima appears about 2.2 degrees from Alpha Centauri, about four times the width of the full Moon. The Gaia space telescope measured Proxima's distance as about 4.25 light-years, and a 2021 study measured Alpha Centauri's as 4.34 light-years. Combining these places Proxima about 12,000 astronomical units from Alpha Centauri A.

The result depends on the small difference between the two distances, so it is less certain than either one. A 2017 study used an older, slightly larger distance for Alpha Centauri and found about 13,000 astronomical units, about 1.9 trillion kilometers. The 2021 measurement placed Alpha Centauri a little closer to us, which brings the two stars closer together.

Size comparisons

The distance is about 12,000 times the average distance from Earth to the Sun.
It is about 13 times the farthest distance of the icy world Sedna from the Sun, which is 937 astronomical units.
Light takes about 70 days to cross it, so it is about 70 light-days, or about one-fifth of a light-year.
If the Sun were shrunk to the size of a basketball, Earth would orbit it about 26 meters (85 feet) away. At that scale, Proxima would be about 310 kilometers (190 miles) from Alpha Centauri A, and both would be about 7,000 kilometers (4,300 miles) from the basketball Sun.
A car driving nonstop at 100 kilometers per hour (62 miles per hour) would take about 2 million years to cover the distance.

Proxima's orbit

Proxima is held by the gravity of Alpha Centauri A and B, so the three stars form a single system. A 2017 study showed this by comparing how fast the stars move through space, and a 2021 study confirmed it with more precise measurements. By the 2021 figures, Proxima takes about 511,000 years to circle the pair once.

Its orbit is a stretched oval. At its closest, Proxima comes within about 4,100 astronomical units of the pair, about a third of its distance today. It is now near the far end of its orbit, which reaches about 12,300 astronomical units. It will next pass closest in about 280,000 years.

A triple star system

The three stars of Alpha Centauri form the nearest star system to the Sun. Alpha Centauri A is a little larger and heavier than the Sun, and B is a little smaller and cooler. Proxima has only about one-eighth of the Sun's mass and is far fainter than the other two. It was discovered in 1915, and astronomers soon noticed that it moves across the sky with Alpha Centauri, at almost the same distance from us.

In 2016, astronomers announced a planet about the mass of Earth orbiting Proxima. It lies in the star's habitable zone, the range of distances from a star where liquid water could exist on a planet's surface.