How Earth Moves

you hey Vsauce Michael here do you have a best friend who is there for you 24/7 365 sorry that's not really good enough if you're a friend truly had your back they would be there for you 24 point zero zero zero zero zero zero six seven three sixty five point two four two one eight nine one also George Washington was born on February 22nd 1732 at least that's what we're told however his family Bible says he was born on February 11th 1730 1/2 so which is it mister I cannot tell a

lie oh and don't even ask about 1752 in Russia 17:52 looked pretty normal but check out what the British Empire was up to that year nothing really out of the ordinary except ember the second was followed by the 14th were eleven days just deleted where'd they go what happened then it is time to question time and how the

earth

moves

reconciling both of these things has led to some pretty strange things we all love time-lapse videos of the stars moving across the sky but really we are the

ones who are tumbling through the universe on a giant wet rock vehicle called

earth

with a windshield called the sky as viewed from above the North Pole we spin counterclockwise west chases east I always remember this by thinking of the US as a weird Mane headed animal with Texas and Florida legs running forward but we don't just spin we also revolve around the Sun on a plane tilted 23.4 degrees relative to our spin it's kind of nauseating at this scale but from this perspective you can

see that the Sun rising and setting is just the

earth

pointing you towards and then away from the Sun this motion causes your sunrise your noon the moment when the Sun is highest in your sky before your Sun set to more closely investigate this movement let's talk about meridians you are on one at this very moment your meridian is just aligned from where you are right now straight towards the North and South Poles it's a line of longitude as opposed to the horizontal lines that lay flat

when north or south is up that we call flat attune or actually latitude the Sun is highest in the sky to you your noon when your Meridian is pointed right at the Sun a cool thing happens at this moment all shadows around you point directly towards one of

Earth

's poles unless you're on the sub solar point the subsolar point is the point on

Earth

's surface directly below the Sun it's always somewhere you can check its current location online links as always in the description on

the subsolar point shadows fall straight down so they can easily disappear twice a year the subsolar point crosses over Hawaii the only place in the US where it hits land and when it does it is called Lahaina noon meaning cool Sun straight vertical objects look unnatural during this brief time like they don't belong as if they were photoshopped in without regard for reality in Honolulu a sculpture by Isamu Noguchi called sky gate casts a twisted shadow all day every day except during Lahaina

noon when its shadow is a perfect circle you may not live in a place where the Sun ever appears directly overhead but once every

Earth

rotation the subsolar point falls somewhere on your Meridian making it noon for you the technical name for this noon for you is local apparent solar noon the clock on your wrist and the clock on your phone don't tell you your local apparent solar time because long ago we realized that if every meridian had its own time a person just a few kilometers away

seeing different shadows than you did would disagree with you on what time it was so town's adopted their own time now later on this trick was standardized and time zones as we know them today came about but that's not all we didn't like about shadow based sundial time to explore deeper we have to begin by asking what's a day I mean obviously it's just the time it takes the

earth

to turn around once right but according to what everything else in space is moving in some way to

the universe doesn't include a convenient sheet of graph paper at Absolute rest we can trace paths on the best we can do on that front is to look at very very far far far away stars so far away like distant features of the landscape out the window of a moving car they barely move as

Earth

does now to them a Meridian on

earth

completes a trip around about once every twenty three point nine hours this is called a side aerial day side aerial means pertaining to the Stars even though the

sidereal day seems pretty clear it's not what our calendars and clocks are based on because there's a nearer star whose position relative to us has a bigger effect on our lives the Sun looking down on the north pole at

Earth

's counterclockwise spin the

earth

also

moves

counterclockwise around the Sun after a sidereal day the

earth

has moved a bit along its orbit so some more rotation is required for the same meridian to point back towards the Sun again this longer definition of one

rotation is what the modern calendar and clock is based on it is called the solar day but here's the thing exactly how long the

earth

has to rotate to complete a solar day changes day to day our clocks are just based on the average amount of time this takes so throughout the year they fall ahead and behind the Sun this is a solar graph a picture of the sun's path across the sky every single day if our clocks actually told us local apparent solar time if you took a picture of the sky

every day at noon you should get a line of Suns but this is what really happens over the course of a year it will appear as though your clock is running slow and then fast and then slow again and then fast again this problem was known since at least ancient times even if its cause was it in order to reconcile the two the equation of time was constructed in this sense equation means to reconcile the equation of time was applied to what a clock said in order to compute the real time the solar time

a sundial would show now some fancy clocks called equation clocks were made that would do this for you but eventually we gave up we gave up and just said no the real time isn't what the Sun says it's what our inventions say now this transition was a big one it was humanity growing up it was like the first time you realize you're stronger than your parents we realized our timepieces were more regular and turned our backs on the timepieces nature had but what causes this disagreement

in the first place as it turns out the answer revolves around revolving the way the

Earth

revolves around the Sun if the Equator faced the Sun all the time and the

earth

always orbited at the same speed the subsolar point would just stay right there on the equator throughout the year and the amount of extra time spent rotating the

earth

needed to do to finish a solar day would always be the same but those two things aren't the case first of all the

Earth

's orbit is slightly elliptical so

its speed varies throughout the year when it's moving around the Sun faster around the beginning of January the amount of extra turning time needed to complete the solar day is longer than when it's further away from the Sun and moving more slowly there's more because the

earth

is tilted the subsolar point is dragged throughout the year in a circle around

Earth

that's not the equator so it changes directly moving northeast then leveling out and going southeast before leveling out

and going northeast again during times of the year when the subsolar point is being dragged by

Earth

's orbit mostly east it gains against

Earth

's spin faster more time is required for the day to finish now by coincidence we are alive at a time when both of these phenomena lengthen and shorten days at roughly the same time so they add up making September 18th almost a minute shorter than the longest day of the year December 22nd for northern hemisphere Ian's December has the shortest

periods of daylight but the whole solar day from sunrise to sunrise is for everyone on

earth

the longest of the year on December 22nd people in the North just spent most of it in darkness

earth

's tilt it doesn't just affect how long a day is it also affects how long a year is this is because the

Earth

's tilt is what causes the seasons for the half of the

earth

tilted towards the Sun the same amount of solar radiation is spread across less space than it is on the other half so there

is more heat energy laid down per area this causes what we call summer and winter for the other half the amount of time from one of these seasonal orientations of the

earth

to its occurrence again is called a solar year or a tropical year it's a very useful way to define a year because it contains every single season exactly since it's based on the very orientations that caused them but the problem is this the number of solar days that occur in a solar year is not a whole number it's

almost 365 but after that many solar days about 1/4 of a day more happens before the solar year starts again this makes designing a calendar more like designing a calendar if your calendar only ever has 365 days in a year over time those dates will drift from the seasonal positions they used to occur during unless hmm this extra quarter of a turn adds up to a full day after four years see March 1st is coming a day too soon now so if we just delay March by adding an extra day at the end of

February every four years a leap day we're back on track leap days do not add days to your life you're still going to live the same number of them they just change what we call them but really who cares about being one day earlier every four years I mean one day isn't much you hardly notice it but over time well if America's founders had declared not only independence from Britain but also from leap days and abolished them from happening today 240 years later their calendar would

be a full two months ahead of

Earth

's position putting America's coldest winter days in April and its hottest summer days in October adding a day every four years is what the famous Julian calendar does introduced in 46 BC by Julius Caesar it was the defacto standardized Western calendar for a very long time more than a millennium but it's not perfect look closely leap days actually move the calendar just slightly too far each time because I lied 365 and a quarter solar days

don't occur within one solar year the real number is slightly less and fluctuates year-to-year based on long-term changes to

earth

and the sun's movements which means adding one day every four years is just a teensy weensy too many by 1582 julian calendar dates were ten days behind the seasons compared to where they used to be that's not bad ten days and more than a millennium and a half but the Catholic Church cared because they wanted Easter to occur exactly when it used to

centuries ago astronomers at the time realized that if leap days pushed the calendar too far behind the seasons we would just need to celebrate fewer of them to fix the problem specifically we would need three fewer leap days every four centuries the rule they wrote to achieve this stated that every four years would continue to be a leap year except if it was divisible by 100 unless it was also evenly divisible by 400 this re

moves

three every 400 years on October 4th Pope Gregory the 13th

introduced this new calendar it took his name the Gregorian calendar he also undid the drift that had occurred since the early days of the Julian and declared on October 4th that tomorrow would be October 15th October 5th to the 14th never happened in 1582 in countries that listened to the Pope it took the rest of the world centuries to hop on board England and its colonies like the soon-to-be United States of America adopted the Gregorian in September of 1750 - by which point their Julian dates

were off from the seasons by 11 days hence the disappearing of the 3rd through 13th when adopted the 1st of the year was also moved from March to January first this explains why George Washington's birthday has two answers although more closely hitched to the seasons than the Julian the Gregorian calendar still isn't perfect its difference causes dates to become one day off from the seasons every 3,000 216 years other calendars have been proposed like the one stand-up maths calculated

that drifts off even more slowly his video is a great watch by the way but enough of all of this let's sit back and enjoy

Earth

's movement without trying to divide it up and name it as a caveat keep in mind that

Earth

's oceans and liquid insides and other celestial bodies are always pulling and tugging and sloshing around minutely changing

Earth

's movements their effect is measurable but difficult to notice at big scales and also don't look like much in the short term short

like the length of a human life looking from above the North Pole the equator spin counterclockwise at about sixteen seventy kilometers per hour relative to the Sun

Earth

orbits counterclockwise at one hundred and eight thousand kilometers per hour along a path tilted 23.4 degrees to it's spin within our local neighborhood of stars our entire solar system is drifting seventy thousand kilometers per hour roughly in the direction of the bright star Vega in the constellation of Lyra and our

solar system is part of a giant galaxy called the Milky Way on a plane tilted about sixty degrees approximately like the windshield of a car looking from above

Earth

's North Pole our entire solar system races clockwise around the galactic center at about seven hundred and ninety two thousand km/h our whole galaxy is also moving through the universe we know this because when the universe was very young it was so hot electrons and protons jumped around and photons of light scattered constantly

they couldn't travel very far before scattering again so the universe was opaque but then around 380,000 years after the Big Bang the universe cooled just enough for electrons and protons to form hydrogen suddenly abruptly photons decoupled from this obstacle course and could travel relatively unencumbered the universe became transparent to light since that moment those early photons have been propagating through space every day ancient photons that last scattered off this opaque fog at the

moment of decoupling a light date further from

Earth

currently is reach us they are part of the cosmic microwave background radiation it is visible in every direction microwave because although they used to be more energetic the universe's expansion has redshifted them now some parts of this radiation are more redshifted than others because of our own movement through the universe controlling for the movements we've already talked about relative to this infinite cooling baby picture of

the universe the first and oldest detectable light we are headed riding along in the Milky Way in the direction that the constellations of Leo and Virgo are to us at a speed of 2.1 million kilometers per hour towards a thing we don't fully understand yet simply called the Great Attractor this is how you on

Earth

's surface are moving through the universe aboard Spaceship

Earth

okay now stop this is roughly 100 years of

Earth

's movement through space this path we trace for where we

began here is the path you will take through the universe in your lifetime you didn't buy a ticket for this ride your parents signed you up without asking but nonetheless it is quite literally the ride of your life and as always thanks for watching it is now time for a major Vsauce announcement you know how for the last couple of years we've released a holiday box well introducing the curiosity box by Vsauce we created this thing as a quarterly box this comes to you four times a year and

it comes packed with amazing exclusive Vsauce merchandise and incredible geeky toys picked by myself Kevin and Jake plus as always a portion of the proceeds from this box goes to funding Alzheimer's research you can get your own by subscribing at the curiosity box com I'm incredibly proud of this go check it out and as always thanks for watching