WTF

Forgot to turn on anti-aliasing, or drawn the star with the Pencil tool instead of the line mode?

Maybe i forgot about AA. Or i just don't like tha way it goes you know. Sharp st8 lines. Next time i'll check if there's button for AA.
And can you please explain how to make it smooth(AA). Talk about that.

Given the pointy ends, assuming the star has been rendered by stroking a path (Edit>Stroke path). If the option is not checked you get the top line, when it is checked, you get the bottom line.



The most obvious aliasing in your picture comes from the slight tilt of the star. If it where upright the top of the branches would have been perfectly horizontal and would not lead to antialiasing. Using guides makes it somewhat easier.

Thank you