In the Effects tab of the Environment and Effects dialog, scroll up to the Lens Effects Parameters rollout. Choose Star from the effects list and move it to the list on the right. A Star effect appears over the Main Sun in the Effects Preview window.
Scroll down to the Star Element rollout, and set the following:
Set Qty (the number of points in the star) to 8.
Set Intensity to 50.0
Set Sharp to 5.0.
Turn on Glow Behind.
Experiment with Width and Taper before setting them to 1.0 and 0.1, respectively.
Improve the star effect by adjusting occlusion settings:
In the Camera viewport, move the Sun omni light so it’s just on the edge of the planet.
Because Interactive is turned on, the rendered frame window updates automatically.
Go to the Lens Effects Parameters rollout and select main sun from the right-hand window.
Scroll down to the Glow Element rollout and set Occlusion to 0.0.
Return to the Lens Effects Parameters rollout and select Ring from the effects list in the right-hand window.
Scroll down to the Ring Elements rollout and set Occlusion to 0.0.