What is that rising sun at the bottom of the fingernail bed?

What is the purpose/function/origin of the lighter colored semi-circle at the bottom of the fingernail bed that looks like a rising sun? It is at the root of the fingernail? Also why such a sharp demarcation between that part and the darker part. I would think that it would be more gradual.What is that rising sun at the bottom of the fingernail bed?
What you are referring to is the lunula of the nail. It is the defining part of the distal edge of the ';free nail.'; What that means is it is the bottom part of the finger nail that is actually showing and above the skin. It is the first part to be seen by the growing nail. This is not the root of the finger nail. The root actually lies under the skin. The part responsible for nail grow is the nail matrix which is actually hidden under the skin and more distal in the finger. The lunula is seen as early as 14 weeks of gestation (when the nails first start to appear). The nail itself is practically colorless. The reason the nail looks pink is because of the tissue and blood underneath. As a medical provider, I look for changes in circulation and perfusion here. This area will be the first to turn purple/blue (cyanotic) due to a decrease in oxygen. You can also see signs of chronic hypoxia and liver disease by examining the nail bed (lunula). Also, its color is a measure of perfusion (of blood) to the distal tips of the fingers. Hope this helps!What is that rising sun at the bottom of the fingernail bed?
its called a lunula...the name came from the idea that this part of the nail looks like a half moon. not all nails have a lunula, but most thumbs do. the lunula is not actually part of the hard part of your nail, it is something on the skin below the nail that is visible through the fingernail. i think it has a role in keratinization, producing the keratin that makes up our nails.
Good question. I only get the rising sun on my thumbs. Once in a while I get little clouds on my fingernails too.