In this Wikipedia article about solar sails, I read the following:
The force on a sail and the actual acceleration of the craft vary by the inverse square of distance from the sun (unless close to the sun), and by the square of the cosine of the angle between the sail force vector and the radial from the sun
This was followed by the equations:
$F = \frac{F_0 \cos^2 \theta} {R^2}$ (perfect sail)
$F = \frac{F_0 (0.349 + 0.662 \cos{2\theta} − 0.011 \cos{4\theta}) } {R^2}$ (realistic sail)
I understand that the second equation is an expansion of the first, taking into account realistic factors that affect the performance of the sail. However I have two doubts here.
- What does "angle between the sail force vector and the radial from the sun" mean?
- What exactly are the realism factors the second equation adds to the first?
- BONUS: What's the best way to graph these equations in order to better understand them?
UPDATE: Could I also get clarification on the variables in the equations and their sources?