The question of how much the Sun grows each day stems from curiosity about the most powerful object in our solar system. The reality is that the Sun is not currently growing in a noticeable or significant way on a human timescale. While the Sun is constantly changing, its size remains remarkably stable over short periods. The daily changes that do occur involve a net loss of mass, not a gain, which is only measurable through careful scientific observation.
The Principle of Solar Stability
The Sun maintains its current size and spherical shape due to a long-term balance of forces. This stability is described by the principle of hydrostatic equilibrium, where the outward pressure precisely counteracts the inward pull of gravity. The immense weight of the solar material constantly attempts to compress the star inward toward its center.
This inward gravitational force is matched by the outward pressure generated by nuclear reactions in the core. The core temperature reaches about 15 million degrees Celsius, allowing hydrogen atoms to fuse into helium. This energy release creates a powerful outward thermal and radiation pressure that props up the Sun against its own gravity. This self-regulating balance keeps the Sun’s radius consistent, preventing it from collapsing or expanding uncontrollably during its current life phase.
Quantifying the Sun’s Daily Mass Loss
While the Sun’s size remains stable, its mass continuously decreases every second, resulting in a net shrinking over vast periods. This mass loss occurs through two primary mechanisms: the conversion of mass into energy via nuclear fusion and the physical ejection of matter into space.
The most significant portion of mass loss comes from energy generation deep within the core. According to Einstein’s relation, \(E=mc^2\), the energy released as light and heat requires a corresponding loss of mass. The Sun converts approximately 4 million metric tons of mass into pure energy every second, accounting for the vast majority of the reduction.
The second method of mass loss is the solar wind, a continuous stream of charged particles that “boil off” the Sun’s super-hot outer atmosphere. This constant outflow ejects an additional 1.5 million metric tons of material into space every second. Combining both mechanisms, the Sun loses about 5.5 million metric tons of mass per second, or over 475 billion metric tons daily. Even at this rate, the Sun has only lost about 0.05% of its total mass over its 4.5-billion-year lifetime.
How the Sun’s Size Changes Over Billions of Years
The Sun’s current stability is characteristic of its main-sequence phase, a period that lasts for nearly 10 billion years. This phase represents only one chapter in the Sun’s stellar life cycle, and its size will change dramatically in the distant future. The gradual depletion of hydrogen fuel will eventually break the stable balance that maintains the Sun’s current size.
As the hydrogen is consumed, the core will become denser and hotter, causing the star to slowly brighten and grow slightly even before it leaves the main sequence. In approximately 5 billion years, the hydrogen fuel will be exhausted, and fusion will begin in a shell surrounding the inert helium core. This change will cause the Sun to expand dramatically into a Red Giant star.
During this Red Giant phase, the Sun’s radius will swell, potentially expanding to engulf the orbits of Mercury, Venus, and possibly Earth. This massive expansion is not a daily growth but a rapid process on a cosmic timescale. After this expansion, the Sun will eventually shed its outer layers and contract into a much smaller, dense white dwarf, about the size of Earth.