Tähtiasemia

Tähtiasemia is a Finnish term that translates to "star positions" or "stellar positions." In astronomy, it refers to the precise locations of stars in the sky at a given moment. These positions are typically expressed using celestial coordinates, most commonly the equatorial coordinate system, which uses right ascension and declination. Right ascension is analogous to longitude on Earth, while declination is analogous to latitude.

The positions of stars are not fixed due to various astronomical phenomena. Stars move through space, and their apparent positions can also be affected by Earth's rotation and orbital motion. Therefore, astronomical observations and calculations often need to account for these changes to determine accurate stellar positions for specific times. Catalogs of stars, such as the Hipparcos catalog or the Gaia catalog, provide extensive lists of tähtiasemia for millions of stars, along with their proper motions, which describe their movement across the celestial sphere over time.

Precise tähtiasemia are crucial for many astronomical applications. They are essential for navigation, both historically using sextants and modern-day through star trackers on spacecraft. They are also fundamental for creating star charts, understanding stellar evolution, and detecting exoplanets. The study of how stellar positions change over time also contributes to our understanding of galactic dynamics and the structure of the Milky Way.