The Figure shows elliptical orbit of a planet m about the sum S. The shaded area SCD is twice the shaded area SAB. If t1 is the time for the planet of move from C to D and t2 is the time to move from A to B then:
t1 = 4t2
t1 = 2t2
t1 = t2
t1 > t2
As we learned in
Kepler's 2nd law -
Area of velocity =
here Angular momentum
So we have
I.e if Angular momentum is conserved then
or we can say that equal areas are swept in equal time
and this is also known as The Law of Equal Areas in Equal Time.
As
If is the time for the planet to move from C to D and
is the time to move from A to B then:
And it is given that (area of SCD) = 2*(Area of SAB)
SO