A 'Star Sapphire' ring. A type of gemstone that exhibits a star-like phenomenon when a bright point source of light is pointed at it - known as an 'asterism' - there you go, two 'astronomy' links! A new one on me, photographed plenty of Moonstone rings, but not one of these before...

https://en.wikipedia.org/wiki/Sapphire#Star_sapphire

So, let's add a Moonstone ring into the mix...

https://en.wikipedia.org/wiki/Moonstone_(gemstone)