I was talking to my wife about the diffraction spikes visible on the stars in the new James Webb images. She pointed out that stars have always been depicted as being spikey and I realized I'd never questioned why that was.
Why did the ancients depict stars such as the Star of David as spikey? Any why did medieval artists do the same? They had such dark skies back then, that they'd have been intimately familiar with the night's sky compared to people of today, but that view would have been with the naked eye and to the naked eye, stars look like point sources and give the impression of being circular.
So why did they depict something like diffraction spikes before they had telescopes?
I would also be curious to see examples of ancient texts describing the appearances of stars, but humans actually do see points of light with diffraction spikes of our own. So, kind of an r/askscience style answer (though it is over 20 years old!) It was theorized this was due to structures in the eyeball, and in 1997 Rafael Navarro and M. Angeles Losada published a paper titled "Shape of stars and optical quality of the human eye," with evidence. They showed a bright point light source in a dark room to test subjects and asked them to draw what they saw, then had a way of photographing the way light spread inside the subjects' eyes, and lastly did some simulations of how suture lines within the eye could diffract light, and found that there were good similarities between all of these. So, humans seeing stars do actually perceive rays extending out from them, as a result of physical properties in the eye, not something imagined.
From their abstract:
These objectively recorded images displayed the distinctive radiating patterns of star images, which were compared with subjective patterns sketched out by the same observers. A strikingly close match was found between the objective and the subjective patterns of the same eyes. In addition, we computed the diffraction patterns produced by a simple schematic model of the suture lines of the anterior lens surface, also obtaining star-shaped images. These results support the commonly accepted hypothesis of a purely optical origin of subjective star images.
The results look to favor a more amorphous, many-pointed star, more like the medieval examples you linked than something as regularly geometric as the Star of David, so, still lots of room to expand on answers for how those stars became commonly accepted. Also would be interested to know if artists thought of stars in the sky as genuinely being pointed, or if they recognized that the rays/twinkling were just an effect you see sometimes.
