Why are Stars Star-Shaped?
Why Physics Stack Exchange recommends it
Physics Stack Exchange users link it when answering or asking about starbursts, beams or spikes around distant lights, since it ties the pattern to diffraction in the eye.
Recommended by 2 people across 2 different months, 2014 to 2022.
What it is
A short MinutePhysics explainer by Henry Reich on why point-like lights such as stars look spiky to the human eye. It attributes the effect to diffraction caused by imperfections in the eye's lens, specifically the Y-shaped suture lines, and cites a paper on optical quality of the eye.
What people said
Recommends Tho Re · 2018-01 · Physics Stack Exchange · on “Why do I see three 'beams' when I look to a distant light source at dark?”
Thanks to agweber's comment which pointed me this Youtube video [this video] , I found the right solution: The cause of this effect are the so called suture lines . A sketch of the lens and these lines can be found here [LINK] . Another image plus an additional video is on this webpage [LINK] (Better watch it only if you can stand medical pictures / videos) There one can really see the Y-shaped suture lines. On that site, they also state that: ... sutures form because of how the lens epithelial cells proliferate during formation. So, the effect is absolutely normal, and no deseases or abnormal defects are responsible for it.
Recommends RC_23 · 2022-09 · Physics Stack Exchange · on “Can anyone explain this peculiar optical phenomina?”
That is caused by your windshield having some type of obstacle or distortion on it perpendicular to the lines of light. If you have light diffract around an obstacle (rather than be blocked by it), it will spread out in the shape of the spatial Fourier transform of the obstacle. This happens most strongly with point light sources. For example, you'll see professional photos using a 6-sided aperature show spotlights with 6 pointed stars. This video covers it with visual examples: [this video]
Cites fibonatic · 2014-12 · Physics Stack Exchange · on “Squinting at street lights”
This [this video] is an informative video, which also relates to the by you mentioned phenomena. However I think it is only/mainly due to the diffraction of the eyelids, since the diffraction pattern would have to be perpendicular to opening.
Cites Sujal Koirala · 2018-09 · Physics Stack Exchange · on “Why does the Sun appear more round while distant stars can appear more pointed?”
In a minute physics video [this video] about the shapes of stars, it mentions that stars in the night sky appear star-shaped due to imperfections in our eyes known as suture lines which cause diffraction. Then why does the Sun looks round? In a source it is written its because the Sun is too close to Earth. But why does the Sun's closeness to Earth matter?