## Why Do We Have Leap Years?

hey there welcome to life noggin

February 29th

is a very special day because it only

appears on the calendar once every four

years or so but why does this happen

well of course it all comes down to

astronomy see a year isn't actually 365

days it's just under 365 and a quarter

but what exactly is a day you learned in

school that a day is the time it takes

for the earth to rotate once on its axis

but with respect to what in order to

define something's motion it always must

be measured relative to something else

let's say we measured the Earth's

rotation with respect to the Sun so we

start counting as soon as the Sun is

highest in the sky and then stop

counting when it reaches that point a

second time this 24-hour period is

called a solar day and it's what we base

our clocks offer but what if we measured

the Earth's rotation with respect to

this day which we call a satiereal day

only takes 23 hours 56 minutes and 4

seconds but why the difference well for

demonstration purposes let's leave the

earth for a moment whoa okay now we're

here there is a massive arrow sticking

out of the earth right now how beautiful

for the earth to rotate a full 360

degrees and end up with the arrow

pointing back at those distant stars

it takes one severeal day but during

that time the earth moves a little bit

in its orbit around the Sun so the arrow

is no longer pointing in that direction

for that to happen the earth needs to

rotate a little bit more which takes

about four minutes so a solar day is

about four minutes longer than a

satiereal day and consequently stars

rise four minutes earlier every night so

now we can define the year that we use

for our calendars a tropical year or the

time it takes to go through all the

seasons is 365 point two for two solar

days that means every four years we have

just under one extra day so we simply

add another one at the end of February

but by doing so we added too much time

and now we're a little ahead so every

100 years we don't have a leap year to

make up for us overcompensating but then

that means we're behind again so every

400 years we add another day in to fix

that mistake and meanwhile all the other

leap years are happy

and if we want to get even weirder a

severeal year is 20 minutes longer than

a tropical year that's because the

Earth's access processes meaning it

spins like a top and if we use this for

our calendars eventually all the seasons

would be shifted around a few months and

unless you live in the southern

hemispheres snow in August is not okay

so anyway when in doubt just remember

that every four years it'll probably be

a leap year so just enjoy the extra day

and leave me a comment letting me know

how you're gonna spend it make sure you

come back every Monday for a brand new

video as always my name is Blanco this

has been life noggin don't forget to

keep on thinking