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動画の字幕をクリックしてすぐ単語の意味を調べられます!
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Hey, Vsauce. Michael here.
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.
コツ:単語をクリックしてすぐ意味を調べられます!

読み込み中…

What Does Earth Look Like?

614 タグ追加 保存
SN Ivagov 2016 年 2 月 25 日 に公開
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