[music] It’s my birthday! [cheering] It’s been a year since we uploaded the very
first video to It’s Okay To Be Smart, and a lot has happened in the meantime. I got
a PhD, I met Bill Nye, I even Neil deGrasse Tyson, I uploaded 2 hours, twenty two hours
and twenty two hours of video and I made a lot of new YouTube friends in the process. I even beat Derek from Veritasium in an epic
YouTube arm-wrestling match. A lot can happen in a year, yet it can seem like no time has
passed at all. Time’s weird like that, it’s kind of like a river, the past keeps floating
away behind us, and the future keeps rushing towards us, yet we’re stuck here paddling
our little boats in the moment we call now. Except as it flows by, each of those nows
becomes a then, you can never quite grab on to them. Instead we must mark our journey with mileposts
of our own invention, seconds minutes, hours, days, weeks, months, and years. How do you measure a year? In daylights, in
sunsets, in midnights, or cups of coffee? I’ve had about 620 cups this year, and since
coffee’s a diuretic, that means I’ve made about 550 liters of urine. I’ve also left behind 325 kilograms of poop,
4 kilograms of skin cells, and 27,000 hairs, most of which I’ve replaced, hopefully. I’m
made a lot more than just YouTube videos this year too, including 3.5 centimeters of fingernails,
15 centimeters of hair, 73 trillion red blood cells, 1400 liters of sweat, 360 liters of
saliva, and 80 liters of tears. A year can also be a distance, the light from
the very first view of my very first video would have traveled 9.5 trillion kilometers
by now, if you and your brain hadn’t gotten in the way first. We’ve also come a long way,
together. Our galaxy is 9.5 billion kilometers closer to our neighboring galaxy, Andromeda,
and our solar system has traveled 7.2 trillion kilometers around the Milky Way. Closer to
home, our moon is 3.8 centimeters farther away from our revolving Earth, which has spun
me around 12.7 million kilometers from here at my latitude in Austin, TX. Earth itself
has traveled 940 million kilometers around the sun. During our trip around the sun, the position
of the stars in the sky changes from night to night. The amount of time it takes a star
or constellation to reach the same point in the sky at the same time of day is 365 days
6 hours 9 minutes 9.76 seconds, or a sidereal year. For most of human history, with people farming
their farms and churches doing their churching, seasons have been the best way to mark a year.
The word “year” actually shares a root with the Greek word “hora” which means “season”.
The tilt of the Earth is what gives us those seasons. Here’s where things get a little complicated.
As Earth spins on its axis, it wobbles a bit like a top. Right now, the north pole points
toward Polaris, but one day in the future, because of that wobble wobble, we’ll have
to pick a new North Star. Of course the universe doesn’t care what we
call winter or summer, and that wobble is out of sync with our trip around the sun.
That means if we based our calendar on sidereal years, the seasons would quickly get out of
sync, Christmas would end up in July, dogs and cats, living together, mass hysteria! Let’s try something different. if we track
the position of the sun in the sky every day, it makes this awesome shape called an analemma,
with two solstices at the top and bottom, and two equinoxes. If we measure the amount
of time between two equinoxes, it ends up being 21 minutes shorter than a sidereal year.
We call that a tropical year, and that’s what we base our calendar on, at least here in
the west. Of course, no one was around in the beginning
to plan any of this planet/solar system stuff, and even a tropical year doesn’t divide up
evenly into days, so we have to correct it with a complex system of leap years, which
CGPGrey explains really well in this video. And that’s even the only way to define a year,
you can find out more about thatin this video from minutephysics. Time is so familiar, but it’s so hard to describe.
Whether we call it a day, a year, or nothing at all, one thing’s for sure, it marches on,
and thanks to entropy, in one direction: forward. Who knows what the next year will bring, or
even tomorrow? I can’t wait to find out. Thanks everybody! Stay curious! Why don’t you take a minute, or an hour, and
take a look back at the past year before it floats too far away.