Since the orbit of the moon is not a perfect circle, there are times when the moon is closer to our planet.

CNN: Rare supermoon eclipse comes Sunday

Here's the explanation: If the Earth made a perfect circle round the sun, the seasons would be almost exactly equal.

NPR: Not All Seasons Are Created Equal

So, I think, there's going to be - sort of actually appreciating almost a perfect circle of that kind of achievement.

NPR: Really Important Football Game Coming

The software is intuitive, so the robot can describe a perfect circle, say, if the operator shows it just a few points.

ECONOMIST: Robots: Nothing to lose but their chains | The

My friends, at every turning point in our history, we, the people, have chosen unity over division, heeding our founders' call to America's eternal mission to form a more perfect union, to widen the circle of opportunity deep in the reach of freedom and strengthen the bonds of our community.

CNN: Clinton: Time again to choose a more perfect union