Tähtien

Tähtien is the Finnish genitive plural of tähdet, meaning "of the stars." In astronomy, tähdet are self-luminous, gravitationally bound spheres of plasma whose energy comes from nuclear fusion in their cores, typically fusing hydrogen into helium. They span a wide range of masses, temperatures, and luminosities and are the primary visible components of most galaxies.

Most tähdet form in giant molecular clouds when regions collapse under gravity, forming protostars that accumulate mass until core temperatures reach the threshold for fusion. They spend most of their lifetimes on the main sequence, fusing hydrogen. Their evolution depends strongly on initial mass; low-mass stars become red giants and end as white dwarfs, while high-mass stars may explode as supernovae.

Stars are studied by observing their brightness, spectra, and parallax. Distance is measured by parallax for nearby stars; more distant measurements rely on standard candles and redshift for extragalactic objects. Spectral classification (O, B, A, F, G, K, M) correlates with temperature and color; the Sun is a G-type star. The light from stars carries information about chemical composition and motion through Doppler shifts.

Stars underpin broader astrophysical processes: they synthesize heavier elements, influence planetary systems, and, through radiation and stellar winds, shape interstellar environments. Cultural and navigational significance is notable across civilizations, with constellations and asterisms used for maritime navigation, calendars, and mythologies.