This point of light in the sky is

Earth as seen from the surface of Mars.

And this is Earth as seen from Saturn.

Here's an image taken only 45,000 kilometres away,

the famous Blue Marble. But what does

Earth really look like?

Well, it depends on how you define "look".

The word look comes from the old Breton word "lagud",

mean eye, the human eye.

And that's part of the problem. Images like this are based on light

humans can see. But we don't see

everything. There's a fantastic episode of Radiolab that uses

sound to illustrate just how different other creature

visual spaces are from our our own. When we talk about the way something

physically looks

we are talking about the visual perception of emitted

or reflected electromagnetic radiation.

Specifically, visible light.

Light we perceive as red has a longer wavelength

than blue or violet. But what if I crank the wavelength

even shorter? Does it stop being light?

No, it just becomes light

you can't see - ultraviolet, X-rays,

gamma rays. Going the other way, you get infrared,

microwaves and finally, radio waves.

In principle, the spectrum of possible

electromagnetic wavelengths is infinite.

But even within the range of wavelengths we observe,

the breadth is breathtaking. If the entire

practical spectrum of wavelengths was laid out

linearly from New York to Los Angeles, the visual portion we see

would only be the size of

100 nanometers. Small enough

to slip through a surgical mask. Point is,

when it comes to what their is to see, our

eyes miss out on lot. For instance,

take a look a remote control. Many of these things communicate with light

of wavelengths we can't see but mobile phone cameras

can. Try this at home. Push a button on a remote control and you won't see much

but use a mobile phone camera to detect wavelengths you can't see

and have them rendered visible. There's a whole lot going on

we miss out on. Our night sky is full of

frequencies we can't see with our eyes alone

but Chromoscope.net allows you to extend

your vision. This is the Milky Way as we see it,

the visible light it gives off. But slide

to see how it would look if our eyes sensed other frequencies.

Of course, we are having to represent these other frequencies

with visible colours because even electromagnetic pretend time

is bounded by our puny limits.

As for Earth, if we only saw infrared frequencies it might look something

like this in our minds. Ultraviolet and extreme

ultraviolet vision would return unrecognizable spheres.

With X-ray vision auroras around the poles would shine brightly

and gamma ray vision would give Earth a bright edge

from high-energy electromagnetic radiation hitting the atmosphere

at a shallow angle.

So, which view is correct? Is there an

absolute true appearance of the Earth?

We haven't even started yet.

Look back at the Blue Marble. What's with the tyranny

of "north" meaning "up"? Perhaps,

it's because we often equate "up" with "better"

and many early map makers were from North of the equator.

But upside-down maps are equally true,

no matter how strange day may seem to us. Funny enough,

the famous Blue Marble itself is a product of North equals

up bias. It didn't originally look like this.

The crew of Apollo 17 originally took it

like this. NASA rotated it to

fit our traditional idea of up after the fact.

Here's a visual birth that comes from the US Naval Observatory's live

animation of our planet. You can see exactly what parts are

in its shadow at this very moment. Other shadows fall

on Earth as well, like the Moon's shadow.

Last week @BadAstronomer shared this image. The dark smudges on the left is

actually

the Moon's shadow during a Solar Eclipse

as seen from above Earth. There's another problem with

the Blue Marble - it's flat and the Earth

is three-dimensional. A globe is the best way to represent the Earth

but globes are difficult to carry around and even when displayed in two

dimensions,

well, you just can't see everything at once.

A flat map of the Earth is really convenient

but requires projecting a globe onto something

flat. And a sphere's surface cannot be represented on a plane

without distortion. The West Wing famously pointed out

the limitations of flat maps.

There's no such thing as a perfect flat map of the entire

world. Some maps are useful for some things and other maps for other things

but it is really fun to pick on the Mercator projection,

mainly because it's so popular and is even used by Google Maps,

mainly because it's so easy to zoom in on.

It preserves shape decently well but suffers

when it comes to area. As I've shown before, Africa

is huge. Its area is so large the entire contiguous United States could

fit inside of it, along with all of China,

India, Japan and much of Europe.

But on the Mercator projection scale near the poles

is pretty wonky, distorted, which means

Greenland appears to be as large as Africa,

even though in reality it is only 1/14th

the size. There's more.

Check out Alaska and Brazil on a Mercator projection. They appear almost

the same size but in reality Brazil

is nearly five times bigger than Alaska.

Areas near the equator are minimized, whereas

areas closer to the poles are exaggerated.

To have fun with this problem, play the Google Maps

Mercator puzzle. The red pieces are countries projected outside of their

usual

locations. Now, what the heck is this

weird shape? Well, let's pull it away from the North Pole, where scale is distorted

a lot

and now it's Australia.

You can see how the math behind map projections distort Earth

by interacting with them on Jason Davies'

brilliant site. Notice how small Greenland appears on the Mercator

projection when pulled down to the

equator and how exaggerated it becomes when moved to the edge.

To be fair, the Mercator projection is great for navigation.

If you want something that is more fair when it comes to area,

try the Gall–Peters. Here,

landmasses are the right relative size

but shape is sacrificed. Everything looks a bit

too narrow.

Enter the Mollweide. This projection shows

equal areas and is a bit more pleasant shape-wise.

If you interrupt the Mollweide around the oceans, relative area is preserved

and the shape of land masses becomes even more

accurate. When it comes to the shortest route between two places on the surface

of the Earth, Gnomonic projections are really cool.

Every straight line journey taken on Earth's surface is actually part of a great

circle. On Mercator projections actual straight line paths

look curved. But every straight line

on a Gnomonic projection is also a straight line

in real life - the shortest route. If you want

a compromise between shape and area, you might try the pleasant

Winkel tripel, which the National Geographic Society has used for maps it

produces

since 1998. Or a beautiful butterfly map

that could be a ball until it's flattened, say, under a pane

of glass. The Dymaxion map can unfold

to show how nearly connected Earth's landmasses

are. It's a great way to visualize human migration

overtime. It's quite impressive how far and wide

humans have traveled on earth, but it remains a bit of a disappointment

to realize just how narrow our slice

of visual perception really is.

But don't feel bad. This brings us to the story of

Julian Bayliss.

Yes, hello, is this doctor Julian Bayliss?

[ON THE PHONE:] Yes, speaking.

Bayliss told me about how one day, while using Google Earth, he

spotted some dark green vegetation.

It looked like a rain forest. An expedition was scheduled

and it turned out to be just that - a rain forest

we had previously never seen. I asked him more.

So, what have you found there?

[ON THE PHONE:] That day we found about 12 new species

just from Mabu. So we found about 3 snakes, 2 chameleons and

about 4 butterflies, 2 new species of plants

and we've only really just been into the forest edge. So, I read, read a paper

the other day, a scientific paper. They estimate that there's maybe 8 million,

8.5 million species in this world but we've only actually discovered

1.5 million or between 1.5 and 2 million.

So, we've actually only discovered maybe one fist of everything that's living on this

planet.

Wow, our eyes only see

a tiny fraction of what there is to see.

But within that tiny fraction there are still

an enormous number of things left to find. So keep searching, keep looking.

[ON THE PHONE:] And as always,

thanks for watching.