will hopefully tell you everything you ever wanted  to know about solar eclipses. Before first, I  

want to talk about my shirt. This shirt shows what  solar eclipses might look like from the surface of  

other planets in the solar system. And to get your  own – go to our store at DFTBA.com/minuteearth. 

Now, on to the main event. A few years ago, I got the chance to  

see something spectacular – it was a  total solar eclipse and it was nothing  

like I expected. When the moon slipped in front of  the sun – perfectly on schedule by the way – the  

little hairs on the back of my neck stood on end.  Like, I knew the eclipse was coming, but despite  

that there's still something very eerie about the  sun vanishing in the middle of the day. Ever since  

then, I have been completely fascinated  by solar eclipses. So when folks from  

NASA's Heliophysics Education Activation Team  reached out to us at MinuteEarth – along with  

Henry at MinutePhysics and Jasper over at  MinuteLabs – to make a bunch of videos and  

an interactive about solar eclipses,  you could say I was over the moon  

about it. Oof. Anyway, over the past year,  we've spent hundreds and hundreds of hours  

researching all sorts of eclipses and making  videos about eclipse-related science. And  

I'm about to take you through all of them. First, I dug into the history of eclipses,  

and I found that eclipses have been  regarded as terrifying omens almost  

as long as humans have been around to see them. These days, we know exactly when eclipses are  

going to happen – we even look forward to  them. But humans didn't learn to predict  

eclipses because they were exciting – it was  because long ago, eclipses were terrifying. 

Hi, I'm Cameron, and this is MinuteEarth. For people living thousands of years ago,  

the sun suddenly vanishing from the sky was a  pretty alarming experience. Even the Chinese  

word for eclipse literally means “to eat”,  as in, the Sun is being eaten by a dragon. 

So it's no wonder that ancient people came  up with all sorts of different explanations  

for both solar and lunar eclipses and tried  to understand when they might happen again. 

About 5000 years ago, people in what  is now England lugged about a hundred  

massive stones through the countryside to  build a structure we now call stonehenge. 

It is mostly composed of an inner ring of large  stones and an outer ring of smaller stones. And  

if you stand in the center of the rings, the  sun appears to rise behind this stone on the  

summer solstice, which shows that stonehenge was  built for watching the sky. There is also a ring  

of 56 post-holes surrounding the monument that, by  moving posts from hole to hole around the circle  

to track the positions of the Sun and moon, could  theoretically have been used to track the timing  

of lunar eclipses, but stonehenge's builders  didn't leave behind an instructions manual,  

so scientists still have a lot of questions  about what the builders intentions were. 

4,000 years ago, Chinese astronomers made  the oldest suspected mention of an eclipse.  

It was the first of roughly 920 solar eclipse  accounts appearing throughout Chinese history.  

However most of the early descriptions  were too vague for modern astronomers  

to pinpoint exactly when they happened. The earliest verifiable eclipse sighting  

was recorded on a 3300-year old clay tablet  that describes a total solar eclipse that  

was seen in the city of Ugarit,  in modern-day Syria, in 1223 BCE. 

Nearly 600 years later, in nearby Babylon,  eclipse watchers would finally figure out the  

pattern that eclipses follow. Lunar eclipses  – that is, when a full moon completely enters  

the Earth's shadow and turns red – were of  great interest to the babylonians' because  

Babylonians saw lunar eclipses as bad omens for  their kings. And it turns out that lunar eclipses  

were the key to spotting eclipse patterns. When the moon passes into the Earth's shadow  

to create a lunar eclipse, the event can be  seen from the entire nighttime half of the  

planet. When the moon casts its shadow on the  Earth during a solar eclipse, the eclipse can  

only be seen from within the moon's shadow. So astronomers in Babylon would see roughly  

half of the lunar eclipses that happened, as  opposed to only a handful of solar eclipses. 

That gave the astronomers enough data  to figure out that lunar eclipses seem  

to repeat every 18 years, 11 days, and eight  hours – a pattern which we now call the saros. 

And it turns out that the saros also applies to  solar eclipses. If a solar eclipse happens here,  

another one with a similar path will be visible  18 years, 11 days, and eight hours later. However,  

because of those extra 8 hours, the earth will  have rotated 120° farther around, and the eclipse  

path will be shifted 120 degrees westward of  the last one. And the same goes for the next  

eclipse in the cycle. And the next and the next  and the… you get the idea. For example, these are  

the similar paths of one repeating set of solar  eclipses during the 20th and 21st centuries. Of  

course, both solar and lunar eclipses happen more  frequently than every 18 years, that's because  

as many as 40 different sets of identical  eclipses are overlapping at any given time. 

These days, we can not only calculate  the timing and path of every eclipse  

that occurred over the last 4000 years; we  can also accurately predict them far into  

the future. Like the solar eclipse that will  happen on September 7, 2974; that at 12:51 pm  

local time, will pass right over Stonehenge. Eclipses used to be so terrifying because – at  

least in part – they happen so rarely. But  again, that led to even more questions – like,  

if the moon orbits Earth once a month,  then why don't we get solar eclipses once a  

month? Turns out, I'm not the only one to wonder. [Henry] The moon orbits the earth once per month,  

which means the moon is on the sun side of  the earth every month. So... "why aren't there  

eclipses every month?" is a question answered  eloquently in a 1757 astronomy book by James  

Ferguson. It's the 18th century equivalent of  "astronomy for dummies," complete with amazing  

illustrations. Here's Ferguson's surprisingly  good 250-year-old explanation for why there  

aren't eclipses every month, illustrated by me. Every Planet and Satellite is illuminated by the  

Sun; and casts a shadow towards that point  of the Heavens which is opposite to the Sun. 

When the Sun's light is so intercepted by the  Moon, that to any place of the Earth the Sun  

appears partly or wholly covered, he is said to  undergo an Eclipse; though properly speaking,  

'tis only an Eclipse of that part of the Earth  where the Moon's shadow falls. When the Sun is  

eclipsed to us, the Moon's Inhabitants on the  side next the Earth (if any such there be) see  

her shadow like a dark spot travelling over the  Earth, about twice as fast as its equatoreal  

parts move, and the same way as they move. If the Moon's Orbit were coincident with  

the Plane of the Ecliptic, in which the  Earth always moves, the Moon's shadow would  

fall upon the Earth at every New Moon, and  eclipse the Sun to some parts of the Earth. 

But one half of the Moon's Orbit is  elevated 5 degrees above the Ecliptic,  

and the other half as much depressed below it:  consequently, the Moon's Orbit intersects the  

Ecliptic in two opposite points called the Moon's  Nodes. When these points are in a line with the  

Sun at New or Full Moon, the Sun, Moon, and Earth  are all in a line; and if the Moon be then New,  

her shadow falls upon the Earth; if Full the  Earth's shadow falls upon her. When the Moon  

[is] more than 17 degrees from either of the  Nodes at [a New Moon], the Moon is then too  

high or too low in her Orbit to cast any part of  her shadow upon the Earth. But when the Moon is  

less than 17 degrees from either Node at the time  of Conjunction, her shadow falls upon the Earth. 

[The moon's] orbit contains 360 degrees; of  which 17 [degrees], the limit of solar Eclipses  

on either side of the Nodes, [is but a small  portion;] and as the Sun passes by the Nodes  

but twice in a year, it is no wonder that  we have so many New Moons without Eclipses. 

[Cameron] All of this eclipse talk is probably  getting you pretty excited to see a total solar  

eclipse. I have got some good news for you – every  year, there are at least two total solar eclipses  

that occur somewhere on our planet, so maybe the  next one will happen near you? I should warn you,  

though – your odds of living close to the  next eclipse, or even the one after – depends  

on your attitude - I mean latitude. Every location on Earth has been in  

the shadow of at least one total eclipse, but  some places experience way more of these events  

than others. Like, someone who lives North  of the equator is about twice as likely to  

see a total eclipse as someone south of  the equator. Why on Earth would that be? 

Hi, I'm Cameron, and this is MinuteEarth. This disparity in total eclipses can only happen  

because of a celestial coincidence; although  the Sun is 400 times bigger than the Moon,  

it's also 400 times farther away from us. So, as  a result – from here on Earth – the Sun and the  

moon appear to be almost exactly the same size. I say “almost” because the Earth's orbit around  

the Sun is not perfectly circular. During  some parts of the year, the Earth is a little  

farther away from the Sun – so the sun appears  slightly smaller than usual. During these times,  

when the Earth, moon and sun line up, it's  easier for the moon to effectively block the sun,  

causing a total eclipse. But other times of the  year, the Earth is closer to the Sun, so the sun  

appears larger than normal. When the Earth, moon,  and sun line up during these times of the year,  

the Sun appears larger and the moon might not  totally block it, creating an annular eclipse,  

which is when the moon turns the sun  into a bright ring of fire in the sky. 

And here's where the North-South divide fits  in. In either hemisphere, eclipses are more  

likely in the summer, when the sun spends  more time above the horizon, since it has to  

be daytime in order to see a solar eclipse. And it just so happens that summer in the  

Northern hemisphere happens at the  farthest-out point of Earth's orbit,  

while Summer in the Southern hemisphere happens  at the closest point. As a result, total eclipses  

are more likely to happen North of the equator; for any given spot in the Northern hemisphere,  

a total eclipse happens, on average, once  every 330 years. In the Southern hemisphere,  

it's more like every 550 years. But even within the Northern hemisphere,  

total eclipses become more frequent with higher  latitudes. There are a few different reasons why  

this might be. For one, at the highest latitudes,  the summer sun rarely dips below the horizon,  

meaning that there is sunlight even at  nighttime, as opposed to lower latitudes  

where nighttime is dark during the summer.  Then there's the curvature of the Earth,  

which causes the moon's shadow to fall at a  shallower angle at higher latitudes; eclipse  

paths near the Arctic circle can be more than  four times wider than eclipses at lower latitudes. 

So statistically, the best place to see a total  eclipse is around 80 degrees north; any given  

place along this line sees a total eclipse every  238 years on average. But remember, all these  

numbers are averages taken over a long period  of time. Carbondale, Illinois – which sits at 38  

degrees North latitude, which should see a total  eclipse every 330 years on average – saw it's most  

recent total eclipse in 2017, yet will get its  next one in 2024. And Christchurch, New Zealand,  

which should get a total eclipse once every  420 years – saw its most recent total eclipse  

nearly two thousand years ago, and will have to  wait another four centuries for its next one. So  

when it comes to seeing a total eclipse, it's not  just about latitude – it's also a matter of luck. 

Total Eclipses might happen somewhat unevenly, or  seemingly randomly across the Earth's landscape.  

And some places get super lucky with them while  others can seem pretty left out. But there is  

one thing you can pretty much always count on  – and that is that eclipses will travel from  

West to East across the landscape for the  most part, which is super weird, isn't it?  

Because both the sun and moon travel east to west. [Henry] The sun rises in the east, the moon rises  

in the east, and the stars rise in the east...  but solar eclipses, oddly, come from the west,  

like the April 2024 North American eclipse, or  the August 2027 North African eclipse. Except,  

*not* all total eclipses come from the west - a  few near the north and south poles actually head  

west for a bit before turning around and then  heading east - all of which seems very weird.  

If eclipses are caused by the sun and the moon,  why don't they behave like the sun and the moon? 

The key to the explanation is that the paths  of the sun and moon through the sky depend  

on the rotational speed of the objects  involved, while the paths of eclipses  

depend on just the plain old straight-line  speed of the moon above the earth's surface. 

Viewed from the north pole, the earth and  moon both rotate counterclockwise - that is,  

towards the east. The path of the moon through the  sky is determined by the line of sight from the  

earth's surface to the moon, and because the earth  is rotating faster than the moon is orbiting,  

the sight line (and the moon) starts  off pointing to the east at moonrise,  

then as the earth rotates the moon appears to pass  overhead and set in the west (even though the moon  

is traveling towards the east the whole time). In contrast, the path of an eclipse is determined  

not by the direction from us to the moon, but  by where the moon's shadow falls on the earth's  

surface, and the moon's shadow just points away  from the sun. The moon is traveling "eastwards"  

around the earth at just over 2000 miles per  hour, and its shadow travels at basically the  

same speed - eastwards at just over 2000 miles  per hour. The earth's surface is also moving  

to the east, but not nearly as quickly - the  surface at the equator is only moving around  

1000 miles per hour, and slower the closer you get  to the poles. The moon's shadow easily outpaces  

the earth's surface's eastward motion, which  means eclipses appear to move from west to east. 

Put another way, the face of the earth is about  8000 miles across, so the moon (and its shadow)  

cross the earth in around 3 and a half hours (and  less near the poles), while any point on the earth  

takes 12 hours to cross the earth - it takes  half a day to rotate halfway around the earth. 

It's kind of weird that the moon can orbit  slower than the earth rotates but travel faster;