Astrophotography: Diffraction Spikes

Diffraction Spikes – the long sharp lines radiating from bright stars in some astrophotographs – are an artifact caused by the vanes suspending the secondary mirror in a Newtonian reflector telescope. They are so common that many people think stars are “supposed” to look that way. Children drawing stars in art works even tend to draw diffraction spikes on their stars.

Pretty or not, they are not supposed to be there. In an optically correct system, stars are points of light, not crosses.

Image cropped from Wikipedia.

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