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Proxima Centauri

Proxima Centauri is a astronomy topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Proxima Centauri rather than just read about it. In short: Proxima Centauri is the nearest star to Earth after the Sun, located 4.25 light-years (1.3 parsecs) away in the southern constellation of Centaurus. Discovered in 1915 by Robert Innes, it is a small, low-mass star, too faint to be seen with the naked eye, with an apparent magnitude of 11.13.

Proxima Centauri — main illustration
Proxima Centauri — illustration

Key takeaways

  • Proxima Centauri belongs to astronomy; place it in that map before memorising details.
  • Learn the definition first, then one example that makes the definition concrete.
  • Connect Proxima Centauri to a quantity you can measure, compute or draw — that is where exam questions come from.
  • Reproduce the core statement of Proxima Centauri from memory before moving on to harder problems.

Reference excerpt

Proxima Centauri is the nearest star to Earth after the Sun, located 4.25 light-years (1.3 parsecs) away in the southern constellation of Centaurus. Discovered in 1915 by Robert Innes, it is a small, low-mass star, too faint to be seen with the naked eye, with an apparent magnitude of 11.13. Proxima Centauri is a member of the Alpha Centauri star system, being identified as component Alpha Centauri C, and is 2.18° southwest of the Alpha Centauri AB pair. It is currently 12,950 AU (0.2 ly) from AB, which it orbits with a period of about 550,000 years. Its Latin name means the 'nearest [star] of Centaurus'. Proxima Centauri is a red dwarf star with a mass about 12.5% of the Sun's mass (M☉), and average density about 33 times that of the Sun. Because of Proxima Centauri's proximity to Earth, its angular diameter can be measured directly. Its actual diameter is about one-seventh (14%) the diameter of the Sun. Although it has a very low average luminosity, Proxima Centauri is a flare star that randomly undergoes 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 internal mixing of its fuel by convection through its core and Proxima's relatively low energy-production rate, mean that it will be a main-sequence star for another four trillion years. Proxima Centauri has two known exoplanets and one candidate exoplanet: Proxima Centauri b, Proxima Centauri d and the disputed Proxima Centauri c. Proxima Centauri b orbits 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 1.06 times that of Earth. Proxima b orbits within Proxima Centauri's habitable zone—the range where temperatures are right for liquid water to exist on its surface—but, because Proxima Centauri is a red dwarf and a flare star, the planet's habitability is highly uncertain. A sub-Earth, Proxima Centauri d, roughly 0.028 AU (4.2 million km) away, orbits it every 5.1 days. A candidate sub-Neptune, Proxima Centauri c, roughly 1.5 AU (220 million km) away from Proxima Centauri, orbits it every 1,900 d (5.2 yr).

General characteristics

Proxima Centauri is a red dwarf, because it belongs to the main sequence on the Hertzsprung–Russell diagram and is of spectral class M5.5. The M5.5 class means that it falls in the low-mass end of M-type dwarf stars, with its hue shifted toward red-yellow by an effective temperature of ~3,000 K. Its absolute visual magnitude, or its visual magnitude as viewed from a distance of 10 parsecs (33 ly), is 15.5. Its total luminosity over all wavelengths is only 0.16% that of the Sun, although when observed in the wavelengths of visible light to which the eye is most sensitive, it is only 0.0056% as luminous as the Sun. More than 85% of its radiated power is at infrared wavelengths. In 2002, optical interferometry with the Very Large Telescope (VLTI) found that the angular diameter of Proxima Centauri is 1.02±0.08 mas. Because its distance is known, the actual diameter of Proxima Centauri can be calculated to be about 1/7 that of the Sun, or 1.5 times that of Jupiter. The star's mass, estimated from stellar theory, is 12.2% M☉, or 129 Jupiter masses (MJ). The mass has been calculated directly, although with less precision, from observations of microlensing events to be 0.150+0.062−0.051 M☉. Lower mass main-sequence stars have higher mean density than higher mass ones, and Proxima Centauri is no exception: it has a mean density of 47.1×103 kg/m3 (47.1 g/cm3), compared with the Sun's mean density of 1.411×103 kg/m3 (1.411 g/cm3). The measured surface gravity of Proxima Centauri, given as the base-10 logarithm of the acceleration in units of cgs, is 5.20. This is 162 times the surface gravity on Earth. A 1998 study of photometric variations indicated that Proxima Centauri completes a full rotation once every 83.5 days. A subsequent time series analysis of chromospheric indicators in 2002 suggested a longer rotation period of 116.6±0.7 days. Later observations of the star's magnetic field subsequently revealed that the star rotates with a period of 89.8±4 days, consistent with a measurement of 92.1+4.2−3.5 days from radial velocity observations; the most recent estimate as of 2026 is 84.9±0.6 days. It is thought to rotate at an inclination of 47°±7° to the line of sight.

… excerpt ends here. Continue reading the full article.

Illustrations

Proxima Centauri illustration
Proxima Centauri: Three visual band light curves for Proxima Centauri are shown, illustrating the variability of Proxima. Plot A shows a superflare which dramatically increased the star's brightness for a few minutes. Plot B shows the relative brightness variation over the course of the star's 83 day rotation period. Plot C shows variation over a 6.8 year period, which may be the length of the star's magnetic activity period. Adapted from Howard et al. (2018)[19] and Mascareño et al. (2016)[20]
Three visual band light curves for Proxima Centauri are shown, illustrating the variability of Proxima. Plot A shows a superflare which dramatically increased the star's brightness for a few minutes. Plot B shows the relative brightness variation over the course of the star's 83 day rotation period. Plot C shows variation over a 6.8 year period, which may be the length of the star's magnetic activity period. Adapted from Howard et al. (2018)[19] and Mascareño et al. (2016)[20]
Proxima Centauri: Alpha Centauri A and B are the bright apparent star to the left, which are in a triple star system with Proxima Centauri, circled in red. The bright star system to the right is the unrelated Beta Centauri.
Alpha Centauri A and B are the bright apparent star to the left, which are in a triple star system with Proxima Centauri, circled in red. The bright star system to the right is the unrelated Beta Centauri.
Proxima Centauri: Orbital plot of Proxima Centauri around the bright apparent star Alpha Centauri AB, with position change marked (in thousands of years).
Orbital plot of Proxima Centauri around the bright apparent star Alpha Centauri AB, with position change marked (in thousands of years).
Proxima Centauri: Proxima Centauri (unlabeled) next to Alpha Centauri on a radar map of all known stellar and substellar objects within 9 light-years (ly), arranged clockwise in hours of right ascension, and marked by distance (▬) and position (◆)
Proxima Centauri (unlabeled) next to Alpha Centauri on a radar map of all known stellar and substellar objects within 9 light-years (ly), arranged clockwise in hours of right ascension, and marked by distance (▬) and position (◆)

Worked examples

Example 1 — a first encounter with Proxima Centauri

Start with the simplest possible case. Write down what Proxima Centauri claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In astronomy, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Proxima Centauri before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Proxima Centauri ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Proxima Centauri

In research
Proxima Centauri appears in astronomy research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry
Engineering practice reuses Proxima Centauri in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom
Proxima Centauri is common in secondary-school and first-year university syllabi. It links to neighbouring topics Alpha Centauri, Astronomical objects discovered in 1915, Centaurus, so understanding it makes those chapters shorter.
In everyday life
Look for Proxima Centauri outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Proxima Centauri in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what Proxima Centauri means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain Proxima Centauri out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Proxima Centauri in simple terms?

Proxima Centauri is the nearest star to Earth after the Sun, located 4.25 light-years (1.3 parsecs) away in the southern constellation of Centaurus. Discovered in 1915 by Robert Innes, it is a small, low-mass star, too faint to be seen with the naked eye, with an apparent magnitude of 11.13.

Why does Proxima Centauri matter?

Because it connects several astronomy ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Proxima Centauri?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Proxima Centauri.

Tags

  • Alpha Centauri
  • Astronomical objects discovered in 1915
  • Centaurus
  • Discoveries by Robert T. A. Innes
  • Emission-line stars
  • Flare stars
  • Gliese and GJ objects
  • Hipparcos objects
  • M-type main-sequence stars
  • Objects with variable star designations
  • Planetary systems with two confirmed planets
  • Proxima Centauri

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