The North Star, known formally as Polaris, is larger, more massive, and intrinsically brighter than the Sun. The Sun is a solitary star of average proportions, providing light and warmth to our solar system. Polaris is the primary star in a triple-star system, and its physical size places it in a different category of stellar evolution. This difference means that while the Sun is a middle-aged, stable star, Polaris represents a much more luminous and evolved stage of a star’s life.
The Scale Comparison: Polaris Versus the Sun
The quantitative differences between the Sun and Polaris are significant. Polaris A, the main star in the system, has a radius estimated to be 37.5 to 46 times that of the Sun. If Polaris were placed at the center of our solar system, its outer layers would extend well past the orbit of Mercury.
The mass difference is not as extreme as the size, but Polaris is significantly heftier, containing approximately 5.4 to 6.5 times the mass of the Sun. This greater mass fuels a tremendous energy output, resulting in a luminosity that is roughly 1,260 to 2,600 times brighter than the Sun. The discrepancy between mass and size illustrates how stars swell dramatically as they age, expanding the star’s diameter without adding much material.
Stellar Classification and Life Cycle
The size difference lies in the distinct evolutionary stages and classifications of the two stars. The Sun is a G-type main sequence star, or Yellow Dwarf, currently fusing hydrogen into helium in a stable, middle-aged phase. This stage represents about 90% of a star’s lifetime, and the Sun is about 4.6 billion years into this process.
Polaris A is classified as an F7 Ib Supergiant or Bright Giant star. This indicates the star is much younger than the Sun, likely only about 55 million years old, but it began its life with much greater mass. Stars with higher initial masses burn through their nuclear fuel at a much faster rate.
Polaris has already exhausted the hydrogen fuel in its core and is expanding outward, characteristic of late stellar life. The star is currently passing through a phase of instability, classifying it as a Cepheid variable star, meaning its brightness subtly pulsates over a period of about four days. This core-hydrogen exhaustion and subsequent expansion transforms the star into a giant or supergiant.
Why Polaris Appears Small
Despite its size and brightness, Polaris appears only moderately bright in the night sky, ranking about 46th brightest overall. This paradox is explained by the star’s immense distance from Earth, located approximately 430 to 450 light-years away.
The light we see has traveled across this vast distance for over four centuries. This distance causes its apparent magnitude—how bright it looks from Earth—to be significantly diminished. If Polaris were the same distance from Earth as the Sun, it would be overwhelmingly bright, but distance transforms the supergiant into a small, steady pinprick of light.
The North Star’s Positional Significance
The fame of Polaris is due to its unique fixed position in the sky, not its size or brightness. Polaris is the current northern Pole Star because it lies nearly in a direct line with Earth’s axis of rotation. This near-perfect alignment means that as Earth spins, Polaris remains almost motionless while all other stars appear to rotate around it.
This stability made it an invaluable reference point for celestial navigation. By measuring the height of Polaris above the horizon, ancient sailors and explorers could accurately determine their latitude. Due to the slow wobble of Earth’s axis, known as precession, Polaris will eventually move away from the pole, but it will remain the Pole Star for many centuries.