Neliöasteina

Neliöasteina is a Finnish term that translates to "in square degrees" in English. It is a unit of angular measure used to quantify the area of a celestial object or a region of the sky. One square degree is the area subtended by a square with sides of one degree in arc length. This unit is particularly useful when discussing the apparent size of astronomical objects, such as stars, nebulae, or galaxies, or when mapping out portions of the celestial sphere.

The concept of square degrees is analogous to the familiar concept of square meters or square feet used for measuring areas on a flat surface, but it is applied to the curved surface of the celestial sphere. The total area of the sky is approximately 41,253 square degrees. This unit helps astronomers communicate the angular extent of phenomena without needing to refer to complex coordinate systems for every measurement. For instance, the Moon subtends an average angular diameter of about 0.5 degrees, meaning its apparent area in the sky is roughly 0.25 square degrees. The full Moon covers approximately 0.2% of the entire sky's area.