Circles of Nature

In nature we see a lot of perfect circles. From the really big...

... like the Sun (here seen through the clouds, which acted as filter, with Sun spots visible):

to those smaller like ... the Moon (not a great picture though):

An finally the really small, like the carpel of a common poppy seen from above:

I know there are spheres and circles which are much bigger and smaller than these but these are just a few of those I took pictures of.