säteilykulmaa

Säteilykulma, often translated as angular width or angular size, is a fundamental concept in astronomy and physics. It refers to the apparent angle that an object subtends in the sky as seen from an observer's perspective. This angle is not a measure of the object's actual physical size but rather its perceived size. For example, while the Sun is vastly larger than the Moon, they appear to have similar säteilykulma from Earth due to their different distances.

The säteilykulma is typically measured in degrees, arcminutes, or arcseconds. One degree is equal to 60 arcminutes, and one arcminute is equal to 60 arcseconds. The formula to calculate säteilykulma (θ) is given by θ = 2 * arctan(r/d), where 'r' is the physical radius of the object and 'd' is its distance from the observer. For small angles, this can be approximated by θ ≈ (2r)/d, where θ is in radians.

Understanding säteilykulma is crucial for various astronomical observations and calculations. It is used to determine the resolution required for telescopes, to estimate the physical sizes of celestial bodies when their distances are known, and to study phenomena like eclipses and transits. For instance, the apparent size of galaxies can vary significantly, impacting how they are observed and classified. Astronomers often refer to the angular diameter of celestial objects, which is twice the säteilykulma.