How does science define a year?

It's been a year since Joe Hanson took his fantastic science tumblr, It's Okay to be Smart, to YouTube. To celebrate, his latest episode takes a look at the ways humans experience years biologically, and how we define them astronomically.

All in all, it's a clever take on the various ways that science – and our understanding of it – can shape our perception and experience of time. Good stuff on everything from the spin of the Earth, to leap seconds, to analemmas, solstices and equinoxes.

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