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Solid angle
- Used to measure FOV
- Unit: steridians
\(\Omega = \frac{A}{r^2}\)
- Solid angle from a person's view to the moon is about the same as that of the sun, which is evident during a solar eclipse
- Solid angle of a sphere measured from any point in its interior is \(4\pi\) steridians.
- Solid angle subtended by a face of a cube to its centre is 1/6th of that, or \(\frac{2\pi}{3}\) steridians.
- Solid angle can also be measured in square degrees
1 sr = \((\frac{180}{\pi})^2\) square degrees
- It can also be measured in square minutes, square seconds or fractions of sphere (\(\frac{1}{4\pi}\)) sr, also known as spat
1 sp = \(4\pi\) sr
- In spherical coordinates,
\(d\Omega = sin(\theta)d\theta d\phi\), where
\(\theta\) is the colatitude (angle from the North Pole) and
\(\phi\) is the longitude