Blood!
What do we know about it?
It’s the favorite drink of the vampire bat!
And, of course, it helps keep you alive, by delivering oxygen to all your body’s cells.
Look at your arm, and you might be able to see some veins through your skin!
Veins have very thin walls, which are almost see-through.
So here’s a curious question: Why do veins sometimes look blue?
If veins are full of blood and blood is red why do veins sometimes look blue?
Well, it’s all a trick of the light.
White light is made up of many different colors.
When the light hits an object, some colors are absorbed and some are reflected back towards your eyes.
So, bananas are yellow because they reflect yellow light, and blood is red because it reflects red light.
However, the blood in your veins is covered by skin and other tissues, which block some colors of light more than others.
Red light goes deeply into the tissue, and is more likely to be absorbed.
While blue light doesn’t go as deep, so is more likely to be reflected.
So that’s why veins filled with red blood ... can sometimes look blue!
White light is made up of different colors.
We only see the colors that are reflected back to our eyes.
The tissues above our veins reflect more blue light than red light.
Got it?
Great – another curious question answered!