Diffraction spike

Diffraction spikes are lines radiating from bright light sources, causing what is known as the starburst effect[1] or sunstars[2] in photographs and in vision.

They are artifacts caused by light diffracting around the support vanes of the secondary mirror in reflecting telescopes, or edges of non-circular camera apertures, and around eyelashes and eyelids in the eye.

Early off-axis designs such as the Herschelian and the Schiefspiegler telescopes have serious limitations such as astigmatism and long focal ratios, which make them useless for research.

Iris diaphragms with moving blades are used in most modern camera lenses to restrict the light received by the film or sensor.

[9] An improperly cleaned lens or cover glass, or one with a fingerprint may have parallel lines which diffract light similarly to support vanes.

[10] They can be distinguished from spikes due to non-circular aperture as they form a prominent smear in a single direction, and from CCD bloom by their oblique angle.

Diffraction spike in normal human vision can also be caused by some fibers in the eye lens sometimes called suture lines.

Diffraction spikes from various stars seen on an image taken by the Hubble Space Telescope
Diffraction spikes caused in James Webb Space Telescope due to its hexagonal aperture and three support struts
The optics of a Newtonian reflector telescope with four spider vanes supporting the secondary mirror. These cause the four-spike diffraction pattern commonly seen in astronomical images.
Apertures blades of camera
Streaks due to a dirty lens
Sun obscured by tree
Near the equinoxes in Chicago sunrise and sunset photography of east–west urban street canyons often features diffraction spikes. Similar Manhattanhenge happenings occur throughout the year around the world.
Effect of a triangular star filter
Use of diffraction spikes to focus a telescope with a Bahtinov mask