During the daytime, a shadow cast by an opaque object illuminated by sunlight has a bluish tinge. This happens because of Rayleigh scattering, the same property that causes the sky to appear blue. The opaque object is able to block the light of the sun, but not the ambient light of the sky which is blue as the atmosphere molecules scatter blue light more effectively. As a result, the shadow appears bluish.
I have a little shadow that goes in and out with me,
And what can be the use of him is more than I can see.
He is very, very like me from the heels up to the head;
And I see him jump before me, when I jump into my bed.
The funniest thing about him is the way he likes to grow-
Not at all like proper children, which is always very slow;
For he sometimes shoots up taller like an india-rubber ball,
And he sometimes gets so little that there’s none of him at all.
He hasn’t got a notion of how children ought to play,
And can only make a fool of me in every sort of way.
He stays so close beside me, he’s a coward, you can see;
I’d think shame to stick to nursie as that shadow sticks to me!
One morning, very early, before the sun was up,
I rose and found the shining dew on every buttercup;
But my lazy little shadow, like an arrant sleepy-head,
Had stayed at home behind me and was fast asleep in bed.
-- Robert Louis StevensonPosted by gerardvanderleun at February 4, 2014 5:29 PM