As usual, wiki has the answer: https://en.wikipedia.org/wiki/Diffraction_spike https://en.wikipedia.org/wiki/Diffraction_spike >"...four spider vanes supporti

As usual, wiki has the answer: https://en.wikipedia.org/wiki/Diffraction_spike https://en.wikipedia.org/wiki/Diffraction_spike >"...four spider vanes supporting the secondary mirror. These cause the four spike diffraction pattern commonly seen in astronomical images."