the.com/steradian
the way math measures how much sky a thing devours from your eyeball
means A steradian is the SI unit of solid angle, measuring the area a cone subtends on the surface of a sphere — specifically, the angle that cuts off an area equal to the square of the radius.
from A 19th-century scientific coinage stitching together the Greek 'stereos' (solid, three-dimensional — the same root behind 'stereo' sound and 'stereoscope') with 'radian,' the flat-angle unit. So it literally reads as 'solid radian': the radian's idea pushed off the page and into three dimensions, measuring not a slice of a circle but a patch of a sphere.
- full sphere
- a complete sphere holds about 12.57 steradians
- the area
- one cuts surface equal to radius squared
- si oddball
- officially dimensionless, yet bossy enough to need a name
- sun's bite
- the sun claims roughly 0.00006 steradians of sky
- radian's cousin
- it's the radian dragged into a second dimension