Small Angle Formula
- If angular and linear diameters known => distance
- orbit of Moon around Earth is an ellipse
- axis of ellipse points to point on celestial sphere
- axis of ellipse precesses -- giving 18 y Saros cycle of eclipses
We automatically use this formula
- car at night
- headlights ~ 4 ft. apart (linear diameter)
- if angular diameter > 2o
- car closer than 100 ft.
- don’t cross that road
- really also need speed of car
- If it’s travelling 6 mph = 9 fps, it is safe to cross
- brain actually knows differential calculus as well as small angle formula to decide if it’s safe to cross the road (deer don’t)
- This method used to measure the distance of Hyades (120 ly)