Pistetähteä

Pistetähteä is a Finnish term that translates to "spotted star" and refers to a celestial phenomenon. It describes the appearance of a star that exhibits noticeable variations in its brightness over a regular period. This variability is not due to external factors like obscuration by interstellar dust, but rather inherent changes within the star itself.

The cause of this spottedness is often attributed to large sunspot-like regions on the star's surface. These regions are cooler and therefore less luminous than the surrounding photosphere, leading to a decrease in the star's overall apparent brightness as these spots rotate into view. As the star continues its rotation, these cooler spots move out of view, and the star's brightness returns to its maximum.

The period of this brightness variation, known as the rotation period, can be used to infer the star's rotational speed. Stars exhibiting pistetähteä are often young, active stars that are still developing their magnetic fields, which are responsible for the formation of these starspots. Studying pistetähteä helps astronomers understand stellar activity, magnetic field evolution, and the internal dynamics of stars. While the term originates from Finnish, the phenomenon itself is observed across various types of stars, particularly those similar to our own Sun but with more pronounced magnetic activity.