Euler line

In any triangle, the orthocenter $H$, the centroid $G$ and the circumcenter $O$ are collinear, and $OG/GH=1/2$. The line passing by these points is known as the Euler line of the triangle.

This line also passes by the center of the nine-point circle (or Feuerbach circle) $N$, and $N$ is the midpoint of $OH$.