Pääjakson

Pääjakson is a Finnish term that translates to "main sequence" in English and refers to a specific stage in the life cycle of stars. It is the longest and most stable phase of a star's existence. During the main sequence, stars generate energy through nuclear fusion in their cores, converting hydrogen into helium. The specific properties of a star on the main sequence, such as its luminosity, temperature, and size, are primarily determined by its initial mass.

Stars are classified on the main sequence according to their spectral type, which is related to their surface temperature. The hottest and most luminous stars are found at the upper left of the main sequence on a Hertzsprung-Russell diagram, while the coolest and least luminous stars are at the lower right. Our Sun is a main sequence star, specifically a G-type star, and has been for billions of years. The duration a star spends on the main sequence varies greatly with its mass. More massive stars burn through their hydrogen fuel much faster and have shorter main sequence lifetimes compared to less massive stars. Once a star exhausts the hydrogen in its core, it will leave the main sequence and evolve into a different stage, such as a red giant or a white dwarf.