If you’re not a morning person, then you’d
probably love living on the moon or out in space! The whole “lack of oxygen” thing aside,
a ‘round-the-clock night sky sounds pretty tempting! But that got me wondering… - Why is there so much light on Earth, but
almost none once you leave our planet? You might think that it’s light during the
day and dark at night because the Earth spins on its axis, and the Sun illuminates either
hemisphere. That’s part of the reason, but it’s more
complicated than that. I mean, our star shines on the Moon too, but
the sky above it is always black! It all comes down to the unique atmosphere
surrounding our Earth. It’s full of dust, dirt, gases, and water
droplets – which all act like tiny mirrors and reflect the sunlight. When sunlight bumps into these small particles,
it diffuses and creates different colors. That’s why we see a blue sky and all those
spectacular shades during sunrise and sunset. - It’s a whole different story elsewhere… If you find yourself on the Moon, where there’s
no atmosphere, the sky will be black. You’ll be able to see the stars even when
the sun is blazing on the surface during the lunar day. The same is true of space. It’s filled with lots of different gases,
but it has no atmosphere with molecules to reflect light. In other words, space is empty. That’s why even when the Sun is shining,
space looks like a black void. If one day the Earth’s atmosphere disappeared,
it’d be just as dark as it is in space or on the Moon. That one’s clear, but the Sun isn’t the
only star (or source of light!) in the Universe. So… - Why don’t other stars shine with blazing
light at night? You’re not the first to wonder about that. An astronomer named Thomas Digges researched
this question back in the 16th century. Digges was sure that the Universe had no end,
and the stars in it could not be counted. He tried to answer why all these innumerable
stars don’t blind us with glaring light… but failed. His questions were just way far ahead of his
time, and he didn’t have the tools to find the answer. In the early 19th century, German astronomer
Wilhelm Olbers suggested that the reason the sky is dark at night was a dusty veil that
hid most of the stars from us. This idea also proved to be wrong later. The stars shed not only light but huge energy
that could heat dust particles so that they would start shining themselves. In that case, the night sky would still be
light because of shining dust. - And yet the sky gets dark every evening
after sunset. What’s bad about this theory then? Digges, Olbers, and other astronomers of the
past believed the Universe was infinite, but modern astronomy knows better. The number of stars, as countless as they
may seem, is simply not enough to illuminate the sky at night. The sky gets dark because the stars, just
as the Universe itself, don’t last forever. They are finite. You see, the Universe has its own borders
and isn’t as ancient as scientists used to think. Sure, just shy of 14 billion years is no whippersnapper
to us humans, but it’s still surprisingly young in cosmic terms. And it’s not much for all the light from
the most distant stars to be able to reach the Earth. - In other words, thanks to our fancy powerful
telescopes, we now know that it takes light billions of years to get to us from the farthest
stars. This means, when we look at the sky, we glance
into a very distant past. Modern telescopes can show us that the light
started its journey to the Earth about 10 billion years ago. The more powerful telescopes get, the further
back in time we can see. One day we’ll be able to see something that
existed before stars appeared, probably by studying the dark gaps between them. But more on that here in a sec! Ok, stars don’t illuminate our night sky
all that much because they’re really old even as we look up at them, and they’re
unimaginably far away. If that’s the case, then… - Why don’t less distant stars shine as
bright as the Sun? There should be thousands of stars much closer
than those on the outskirts of the Universe. Yeah, sure, there are plenty! Let’s take a look at our closest space neighbor,
Proxima Centauri, as an example. It’s practically in our back yard, just
over 4 light-years away from us. But we can’t even see it in the sky without
a telescope! The thing is, it’s 7 times smaller than
our Sun, and it gives off only a fraction of 1% of the Sun’s brightness. And our “close” neighbor just 4 light-years
down the road is still pretty far away – about 25 trillion miles. For comparison, our own big bright Sun is
a “mere” 93 million miles from Earth. So, our star is much bigger and closer. Other stars might be brighter than the Sun,
but they’re much farther from us too. - But don’t all those distant stars give
at least some noticeable light on this planet? I’ll put it this way: it’d be like switching
on a ton of tiny halogen light bulbs. They’re not as bright as one big LED bulb,
but they do give off part of its light. So, yeah, they give us a little bit of something,
but it’s barely noticeable. Remember, space might be empty compared to
the Earth’s atmosphere, but there are a lot of gases out there. They move around, form clouds, and serve as
a sort of veil hiding most of the light in the Milky Way. That’s why we can’t see everything that’s
going on in our galaxy – we need special equipment for that. But it turns out, Olbers was sort of right,
only the curtain that covers the light is made of gas and not dust! - Where the Big Bang comes into play. The theory states that the Universe was born
in a Big Bang 13.8 billion years ago. Since that time, everything has been moving
away from the point where it all began. That is, the Universe is expanding, and objects
within it are getting farther from each other with time. Sources of light also move away and spread
out, which means space is getting darker, and the number of black areas is growing. They move at their own speed for billions
of years, and our telescopes and satellites, fancy as they may be, can’t notice or track
this movement. - How do we know these black areas exists
at all if astronomers can’t see them? To simplify that for the sake of time, they
study how visible objects behave. How celestial bodies move along an elliptical
orbit around stars or have gravity. This can only be explained with the presence
of an unknown space object or group of objects. Astronomers think that most of the matter
in the universe is invisible, and it looks like black emptiness to the human eye. - But how does it look through a telescope? Oooh, all that blackness lights up in a wondrous
rainbow of colors! We can’t see it because our sight is limited
to the visible light spectrum. But if you remember the electromagnetic spectrum
from back in school, you’ll know that visible light is just a tiny sliver of all those wavelengths
and frequencies. There’s radio, microwave, infrared, ultraviolet,
X-ray, and gamma rays. They’re beyond the visible spectrum, but
all of them exist in space and can be registered by modern telescopes. And what they show us are seemingly dark or
invisible nebulae lit up with every color you can imagine! Red, blue, purple, yellow, orange – the
whole color wheel depending on which gases make them up! Who knows, maybe one day we’ll have special
glasses that let us see all the colors of space just from looking up at the night sky! Hey, if you learned something new today, then
give the video a like and share it with a friend! And here are some other cool videos I think
you'll enjoy. Just click to the left or right, and stay
on the Bright Side of life!
