Primäärisarja

Primäärisarja refers to the main sequence phase of a star's life, a period where it fuses hydrogen into helium in its core. This is the longest and most stable phase for most stars, including our Sun. The position of a star on the main sequence is primarily determined by its mass, which dictates its luminosity, temperature, and spectral type. More massive stars are hotter, brighter, and have shorter main-sequence lifetimes compared to less massive stars.

During the main sequence, a star is in hydrostatic equilibrium, with the outward pressure from nuclear fusion balancing the inward pull of gravity. This balance allows the star to maintain a consistent size and energy output for millions or billions of years. The star's color ranges from red for cooler, less massive stars to blue for hotter, more massive stars. The Sun, a G-type main-sequence star, is yellow and has an estimated main-sequence lifetime of about 10 billion years.

When a star exhausts the hydrogen in its core, it leaves the main sequence and begins to evolve into other stages, such as a red giant or supergiant, depending on its initial mass. The study of the main sequence is fundamental to understanding stellar evolution and the Hertzsprung-Russell diagram, which plots stars based on their luminosity and spectral type.