What is a key feature of visual binaries in astronomy?

Visual binaries are a type of binary star system where both stars can be individually resolved through telescopes. This resolution allows astronomers to directly observe the two stars orbiting around a common center of mass. The key feature here is that the separation between the two stars can be measured directly as they move in their orbits, providing valuable information about their characteristics, such as mass and distance.

In contrast to other types of binary star systems, such as eclipsing binaries, where stars are not always visible simultaneously, or spectroscopic binaries, which require the analysis of spectral lines to infer the presence of two stars, visual binaries allow for direct visual observation of the components. This makes it possible to obtain precise angular measurements, leading to a better understanding of their orbits and physical properties.