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On July, 4th, 1054, Chinese astronomers noticed a new star. Located in constellation Taurus
it became the brightest star in the night sky practically overnight. And it stayed that
way for more then 23 days. It was so bright that it could be seen even during daytime.
And then it disappeared... Using their records we can now point our telescopes
in the exact same spot where that 'guest star' appeared and we can see this...
A crab nebula. They didn't know it back then, but they actually
saw a star explode 6500ly away from them.
When you look up at the night sky you can see many stars... on a clear night with no
light pollution, around 3000 in total. On the other hand if you live in a populated
area, like a city, then you can't expect to see even a 100 or so...
Of course a 100 or 3000 is just a small... small fraction of the total number of stars
in the universe. It has been estimated that there are over 10(23) stars in observable
universe... that's 1 followed by 23 zeros. You know how much that is... if this ball
is a sun then you can fill up... wait that's a bad example. If you were to start counting,
and you count 1 million stars each second, you will count all the stars in the universe
in 3 billion years...
There are many stars in the universe... and stars are really big! If you were to walk
across the equator of earth you will make a full circle in just over 300 days ... on
the other hand, if you were to do the same on our sun, you will make a full circle in
100 years... And our sun is considered to be below average
when it comes to size.
Even though our sun is one of the smaller ones, it's still brighter then the most of
the stars in our milky way... (85%). But you know what is even brighter? Eta Carinae...
Located in constellation Carina it is 7500ly away and it is shining brightly... it is a
million times brighter then our sun... and it's 250 times bigger ... if we were to replace
our sun with it, we would all go blind because the earth would orbit inside of it...
Since it's so big skyenthists are expecting it to go supernova any moment now... of course,
when we speak about events like this, any moment can mean from 1 year to a million years...
But no matter when it goes supernova...it will be one of the most spectacular things
that our astronomers have ever observed. In less then a few seconds... the whole star
will shrink down and collapse in on itself creating mind-blowing pressures and then explode
with such immense force that we would see that explosion here on earth with naked eyes...
during daytime. from 7500ly away Most of the star will be blow away into interstellar
space but something will remain...
A neutron star... Made entirely by neutrons squished together
so compactly that the average density can be as high as 6 times 10(17) kg/meter(3)...
in other words, that thing is so dense that it boggles the mind. And it's so small.
Compare the size of Eta Carinae now and the neutron star that it will leave behind...
it's just a few km across yet it's surface-gravity is a 100 billion times stronger then here
on earth... In other words, if you weight 75kg here on earth, on neutron star you will
weigh way more then the whole Mount Everest...
Small size of the star allows it to spin very fast... the fastest one we've found spun at
the staggering rate of 642 revolutions ... per second... Imagine standing on a star that
spins that fast, imagine looking at the sky... all you would see would probably be just a
blur. Stars - distance
We can't see many stars nowadays... we've polluted our skies with light.. (light map
)and even though stars are bright, they are very far away and thus they can't compete
with the street lamp in front of your house. The closest star to us is... Alpha Centauri,
located only 4.3 ly away! And that's more then 40,000,000,000km! And that's the closest
one! Stars are very far apart. That's why when
the Andromeda Galaxy collides with our galaxy we are not going to see any star collisions
at all because they are so spaced out.
In 1905, one very smart man gave us the way to understand stars... his name was Albert
Einstein and he gave us this equation ... E=mc2 Stars don't burn! In other words, stars are
not big balls of hydrogen on fire. No. They are thermonuclear beasts. In the core of every
single star, in the process of nuclear fusion, matter is converted into energy. And that
energy gets transferred by photons.
But this photons are old... If you watch this during daytime, the light
that enters your eyes from the sun is 10 to 200 thousand years old. This is because when
light get's created in the center of our sun, it cannot just go out... it must bump it's
way to the surface through all these atoms and molecules around
And then, only then when it comes to the surface it can go at the speed of light towards us.
So we are very lucky to see that light at all... I mean, that light fought for thousands
and thousands of years to get out of the sun just to land on your retina so you don't have
to use flashlight all the time.
Solar eclipses are scary cool. One of the mind-blowing coincidences of our solar system
is that our Sun is 400 times bigger then our Moon and it's 400 times further... that's
why they appear almost the same size on our sky and allow us to see this... Astronauts
aboard ISS can see something more... they can see the shadow a solar eclipse makes on
the earth. Even though they are scary cool, you shouldn't
be looking at them with naked eyes... The moon blocks most of the sunlight and our pupils
dilate to adjust.... that's why the sunlight that still passes around the moon can easily
hit our eyes and damage them... if you look at the full solar eclipse your eyes will receive
10 times more light then if you look straight at the sun... that's why it's so dangerous!
However it's still extremely cool! Thanks for watching!