If the angular momentum of a planet of mass m moving around the Sun in a circular orbit is L about the center of the Sun, its areal velocity is:

The areal velocity is defined as the rate at which the radius vector sweeps out area. For a planet in a circular orbit, the areal velocity is given by:
Areal velocity = (1/2) * r * v
where r is the radius of the orbit and v is the orbital speed.
The angular momentum L of the planet is given by:
L = mrv
Solving for v:
v = L/(mr)
Substituting this into the areal velocity equation:
Areal velocity = (1/2) * r * (L/(mr)) = L/(2m)
Therefore, the areal velocity is L/(2m).