What does barycentre mean?
A barycentre is the centre of mass of a system of bodies or particles — the single point at which the system's entire mass can be treated as concentrated, and the point about which the system balances. The term appears most often in physics and astronomy, where it describes the pivot around which orbiting objects move. Crucially, orbiting bodies do not circle each other's centres exactly; instead, they both revolve around their shared barycentre. For the Earth–Moon pair this point lies within the Earth, but for massive pairs such as Pluto and Charon, or the Sun and Jupiter, it can fall at or beyond the larger body's surface. The word is formal and scientific in register, more common in British English than American English, where 'center of mass' is the usual equivalent. Understanding the barycentre is essential to celestial mechanics, orbital prediction, and any analysis of how distributed masses behave under gravity.
nounThe centre of mass of a system of bodies or particles; the point about which the masses of a system balance. In astronomy, it often refers to the common point around which two or more orbiting bodies revolve.
- The centre of mass of a physical system of particles or bodies, the point at which the total mass may be regarded as concentrated.
- In astronomy, the common point around which two or more celestial bodies orbit, such as the Earth–Moon or Sun–Jupiter barycentre.
"The Earth and the Moon both orbit their shared barycentre, which lies just inside the Earth."
"Because Jupiter is so massive, the barycentre of the Sun–Jupiter system lies just outside the surface of the Sun."
"Engineers calculated the barycentre of the spacecraft to plan its rotation and stability in orbit."
The plural is regular and typically appears when discussing several systems, each with its own centre of mass.
"Astronomers computed the barycentres of all the binary star systems in the cluster."
The Earth doesn't sit still while the Moon circles it — both actually wobble around a point called the barycentre, which for the Earth–Moon pair still lies inside the Earth itself.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Etymology of barycentre
Barycentre derives from Greek roots: 'barys', meaning 'heavy', combined with 'kentron', meaning 'sharp point' or 'centre'. The same Greek root 'barys' gives English words such as baritone, baryon, isobar, and barometer. The term entered scientific usage through European astronomy and mechanics, and remains the standard term for centre of mass in much of continental Europe and Britain.
Related word forms
How barycentre is actually used
Barycentre is a technical term used chiefly in physics, astronomy, and mathematics, and is far more common in British usage than American usage, where 'center of mass' is preferred. It carries no emotional connotation and belongs to formal, scientific register.
Easily confused with barycentre
A centroid is the geometric centre of a shape or region considered purely as a figure, whereas a barycentre is the centre of mass of a physical system and depends on how mass is distributed.