Was looking at a photography book talking about extreme exposure with some photos of rotating starfield, star trail. After some test, I found two easy method to make star trail in photoshop.

Method 1
Painting some stars, then manually duplicate and rotate transform the layers. CTRL-SHIFT-T is the shortcut to re-apply the last transform. This method give better result, but we have to repeat the steps a lot of time to produce the star trail.

Method 2
Paint some few stars, apply radial blur. This method is easier, but result are not as good. Because it tends to produce low alpha star trail due to the blur

Painting video:
https://www.youtube.com/watch?v=m35kA0rpd3Y