Longer video on steradian or solid angle. I’m going to fill myself to overflowing with hearing different teachers teach the same subject as:
a) Now it’s a standard.
b) It’s an Ideal, which usually I fight against.
c) I can see how radius moves to chosen angle which rotates around itself to form a cone
d) This cone does NOT automatically extend to INFINITY as it starts with a radius which means:
e) This cone STOPS at the edge of a sphere.
f) This sphere has a surface from within which the solid angle distinguishes itself.
g) The circle that forms at the surface of the sphere from within is radius squared.
h) You can turn that radius squared into a 2D square, with equal length and height.
i) This square follows the inverse square law (1 : 4 : 9 : 25 etc) as it continues as far as you need it to go.
So, What’s special?
a) Chosen angle
b) It’s in a sphere
c) A circle is made with this.
d) The circle becomes a square.
e) That square keeps moving outwards.
f) It’s standard now.