The star figure 
composed of three equilateral
triangles rotated at angles 
, 
, and 
. It has been called the star of Goliath by analogy
with the star of David (i.e., hexagram).
Nonagram
See also
Hexagram, Nonagon, Polygram, Star Figure, Trigonometry Angles--Pi/9Explore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Nonagram." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/Nonagram.html