1 - History of Our Universe Part 1 (for schools)
Summary
TLDRThis video script delves into the evolution of human understanding of the cosmos. From ancient guesses to scientific methods like triangulation and spectroscopy, it outlines how we've measured the universe's scale and age. It highlights key discoveries, such as Eratosthenes calculating Earth's diameter, Kepler's planetary laws, and Hubble's observation of an expanding universe. The script also touches on the Doppler effect and the Big Bang theory, emphasizing the importance of observation and measurement over speculation.
Takeaways
- 🌌 For a hundred thousand years, humans have been fascinated by the stars in the night sky and have speculated about their nature without the aid of technology.
- 🔍 The Greek scientist Eratosthenes was one of the first to attempt to measure the Earth's diameter using shadows and the position of the Sun.
- 🌍 The belief in a geocentric universe was challenged by observations of planets with erratic orbits, which were later explained by Kepler's laws of planetary motion.
- 🔭 The invention of the telescope allowed for more detailed observations of the planets, which were found to be different from the fixed stars.
- 📏 In the 18th century, the transit of Venus was used to calculate the distance to the Sun and, by extension, the distances of the known planets.
- 🛰 Triangulation, a method for measuring distances on Earth, was adapted for measuring the distances to stars by using the Earth's orbit around the Sun as a baseline.
- 🌠 The first star to have its distance measured using triangulation was 61 Cygni, found to be 10.3 light-years away by the astronomer Bessel in 1838.
- 🌟 Astronomers used the relationship between a star's brightness and its distance to estimate the distances of fainter stars, expanding our understanding of the universe's scale.
- 💥 The observation of a supernova in 1987 and its interaction with a surrounding gas cloud allowed for the measurement of distances on a galactic scale.
- 🧪 The study of atomic spectra revealed the composition of stars, with helium being discovered as an element in the Sun's spectrum.
- 🌌 The Andromeda galaxy was confirmed to be outside our own Milky Way, and its distance placed it millions of light-years away, indicating the universe is vast.
- 🌪 Edwin Hubble's observations confirmed that galaxies are moving away from us, indicating an expanding universe, which led to the Big Bang theory.
- 🔬 The Doppler effect, observable in both sound and light, allows astronomers to determine the speed and direction of galaxies, contributing to our understanding of the universe's expansion.
- 🔮 The current understanding of the universe's scale and age is based on extensive observation and measurement, rather than mere speculation.
Q & A
What was the first scientific attempt to measure the Earth's size?
-The first scientific attempt to measure the Earth's size was made by the Greek scientist Eratosthenes of Cyrene II. He used the shadow cast by the Sun at Syene and Alexandria to calculate the Earth's diameter.
How did Johannes Kepler contribute to our understanding of the solar system?
-Johannes Kepler calculated the exact orbits of the planets and formulated the laws of planetary motion, which provided a model of the solar system that fit the observations.
What is triangulation and how was it used to measure the distance to stars?
-Triangulation is a method used to measure distant objects by taking angle measurements from two different points. In astronomy, the baseline is the Earth's orbit around the Sun, and by taking angle measurements at different times of the year, astronomers can calculate the distance to stars using trigonometric calculations.
What was the significance of the 1838 observation of 61 Cygni by the Prussian astronomer Bessel?
-The observation of 61 Cygni by Bessel in 1838 was significant because it was the first time the distance to a star was accurately measured using triangulation. The star was found to be 10.3 light-years away, which greatly expanded our understanding of the size of the universe.
How do astronomers estimate the distance to fainter stars using brightness?
-Astronomers use the relationship between a star's distance and its brightness, where closer stars are generally brighter than distant ones. By calculating the apparent brightness of a star and comparing it to its known absolute brightness, they can estimate the distance to the star.
What is a supernova and how does it help in measuring cosmic distances?
-A supernova is a massive explosion of a star that outshines an entire galaxy temporarily. It helps in measuring cosmic distances because its brightness can be used as a standard candle. By observing a supernova and its light curve, astronomers can determine its peak luminosity and use it to calculate the distance to the supernova and its host galaxy.
How did the observation of a supernova in 1987 contribute to our understanding of the universe's scale?
-The observation of a supernova in 1987 allowed astronomers to measure the distance to the supernova and the surrounding gas cloud using the light echo method. This measurement confirmed that the supernova was 160,000 light-years away, providing evidence that our universe is vast and expanding.
What is the significance of spectral lines in understanding the composition of stars?
-Spectral lines are patterns of light absorption or emission that occur when an atom emits or absorbs light at specific wavelengths. By analyzing these lines through a spectroscope, scientists can identify the elements present in stars, such as hydrogen and helium, which are the most abundant elements in the universe.
How did Edwin Hubble's observations contribute to the theory of an expanding universe?
-Edwin Hubble observed that galaxies were moving away from us at speeds proportional to their distance, a phenomenon known as Hubble's Law. This observation supported the theory of an expanding universe and provided evidence for the Big Bang theory.
What is the Doppler effect, and how does it relate to the observation of galaxies?
-The Doppler effect is the change in frequency or wavelength of a wave in relation to an observer who is moving relative to the wave source. In astronomy, the Doppler effect causes the spectral lines of galaxies to shift towards the red or blue end of the spectrum, depending on whether the galaxy is moving away from or towards us. This shift allows astronomers to calculate the speed and direction of galaxies in the universe.
What is the current scientific understanding of the age of the universe?
-The current scientific understanding, based on observations and measurements, suggests that the universe is approximately 13.8 billion years old, with the start of its expansion marked by the Big Bang.
Outlines
🌌 Humans' Curiosity About the Cosmos
For thousands of years, humans gazed at the stars, often attributing their existence to magical beings due to a lack of technology. However, scientific progress, like observation and measurement, has allowed us to replace guesses with knowledge. The Greek scientist Eratosthenes was one of the first to calculate Earth's size using shadows. Despite the church’s endorsement of a fixed Earth, observable evidence and technological advancements, like Kepler's laws of planetary motion and telescopes, began to reshape our understanding of the solar system and the vast distances of stars.
🔭 Measuring the Distance of Stars
Early astronomers used triangulation to measure the distance of stars, an approach initially limited by technological constraints. However, in 1838, astronomer Friedrich Bessel succeeded in calculating the distance to the binary star system 61 Cygni, marking a significant leap in understanding. By correlating a star's brightness with its distance, astronomers estimated the size of the universe. This understanding expanded further when a supernova explosion was observed in 1987, and triangulation was again used to measure the massive distance of 169,000 light-years.
Mindmap
Keywords
💡Observation
💡Measurement
💡Calculation
💡Triangulation
💡Spectroscopic Analysis
💡Supernova
💡Doppler Effect
💡Big Bang
💡Helium
💡Cosmology
Highlights
For 100,000 years, humans have looked at the night sky, wondering about the stars.
Eratosthenes of Cyrene used shadows to calculate Earth's diameter, marking one of the earliest attempts to measure our world.
Kepler's laws of planetary motion transformed the way we understood the solar system.
Triangulation helped measure distances between stars and established how far away binary stars were.
The first measurement of a star's distance was made in 1838, revealing the binary stars 61 Cygni were 10.3 light years away.
The discovery of supernova explosions allowed scientists to measure distances beyond 100 light years.
In 1987, the supernova explosion within the Milky Way was used to calculate distances using triangulation, showing the universe's vast size.
Pierre-Jules-César Janssen’s spectroscopic study in 1868 revealed helium, a previously unknown element, in the sun.
Andromeda’s supernova in 1917 proved that galaxies existed beyond the Milky Way.
Edwin Hubble’s discovery that the universe is expanding radically changed our understanding of the cosmos.
The Doppler effect explains how scientists use red and blue shifts in light to determine galaxies' movement and speed.
The Big Bang theory explains how the universe expanded from a single point around 14 billion years ago.
The vastness of the universe, now measured in millions of light years, dwarfs early human guesses.
Modern astronomy's key achievement is replacing speculation with knowledge, thanks to observation, measurement, and calculation.
Humans today no longer guess about the universe—they know, thanks to centuries of scientific advancements.
Transcripts
[Music]
for a hundred thousand years humans have
looked up at the night sky and wondered
about those awesome points of light what
are they what are they made of how did
they get there they didn't have the
technology to find out
so they guessed that magical beings had
created it all if you prefer making wild
guesses instead of using observation
measurement and calculation then here's
a sealed box spend the next 10 minutes
guessing what's inside and come back
again at the end of this video because
this video doesn't cover what we guess
about the universe but what we know and
more importantly how we know it how do
we know where the stars and galaxies
came from and how old they are the first
person to take a stab at gauging the
scale of the world around him was the
Greek scientist
Eratosthenes of Cyrene II he knew that
on the longest day of the year the Sun
was directly overhead at Syene in the
south of Egypt but cast a shadow in
Alexandria to the north by measuring the
length of the shadow he can work out the
Earth's diameter but while the earth
might be spherical the dogma of a fixed
earth still held sway backed by a
powerful church problem was this didn't
fit the observable evidence especially
the observation that some wandering
stars or planets in Greek had very
erratic orbits around the earth when the
telescope was invented these planets
turned out to be very different to the
fixed stars but it wasn't until Johannes
Kepler calculated the exact orbits of
the planets than a model of the solar
system at last fit the observations his
law of planetary motion turned this into
this in the 18th century a transit of
Venus across the Sun timed at opposite
ends of the earth made it possible to
calculate the exact distance of the Sun
and by extension the distances of all
the known planets but that still left
the Stars the easiest way to measure
their
distance is a system called
triangulation which is used to measure
distant objects on earth with stars the
base line is the Earth's orbit around
the Sun take an angle measurement here
and six months later here and just do
the math this principle was known in the
17th century that their instruments
simply weren't accurate enough to
measure such a tiny angle but in 1838
the technology had caught up the
Prussian astronomer Bessel found that
the binary stars 61 Cygni was an
astounding 60 trillion miles away it was
a distance so huge that it had to be
measured in terms of the number of years
it took light to cross it ten point
three lightyears
our universe just got bigger
triangulation only works for stars up to
a hundred light years away but it was a
start knowing the distances of these
stars astronomers could work out the
relationship between a star's distance
and its brightness because closer stars
are generally brighter than distant ones
using this calculation they could now
estimate the distance of the fainter
stars they could see it was only an
estimate but I universe got bigger again
we seem to be on the edge of a huge
wheel of stars in space while the
brightness of a star gives us an
estimate of its distance confirmation
comes in another trick of triangulation
in 1987 a star was seen to explode
inside our galaxy the exploding star is
called a supernova and it's very bright
as it happened this particular supernova
was surrounded by a huge gas cloud far
out into space the light from the
exploding supernova raced across the gap
and eight months later it hit the
surrounding gas cloud cosmologists saw
the reflected glow we know the speed of
light so we know how far it can travel
in eight months and that means we know
the distance between the supernova and
the gas cloud all cosmologists had to do
is measure the angle between the two as
seen from Earth and once again it's
simple triangulation we can work out the
distance of the supernova one hundred
and sixty nine thousand light-years that
means we're looking at enough
that happened a hundred and sixty nine
thousand years ago our universe was now
huge by simply observing and measuring
we'd calculated a scale in time and
space that was far greater than Bronze
Age people ever imagined but one
question still confounded scientists
what are all these stars made of to
understand the evidence we have to
understand the atom there are around 92
different types of atom known as
elements they differ in the number of
electrons protons and neutrons they have
when an atom emits light it absorbs the
light of particular wavelengths each
element absorbs a different set of
wavelengths we can see these absorption
patterns as lines when we look through
an instrument called a spectroscope this
one shows the spectral lines of three
elements that were very familiar to
early 19th century scientists hydrogen
lithium and oxygen but when the French
astronomer pierre-jean s'en pointed a
spectroscope at the Sun in 1868 he found
a set of spectral lines no one had ever
seen before it was a completely unknown
element he called it helium after the
Greek word Helios the Sun the new
element also showed up in stars along
with another abundant element hydrogen
inside this tightly bound universe which
they called the galaxy astronomers could
see strange swirling clouds through
their telescopes some astronomers
thought these could be other galaxies
just like our own in 1917 a supernova
was seen to explode inside a cloud
called Andromeda supernovae are usually
very bright but this one was quite faint
using the brightness and distance
calculation cosmologists work out just
how far away Andromeda was two million
light-years that put it well outside our
own galaxy and triangulation showed just
how big it was about the size of our own
galaxy the universe it turned out
extended well beyond our own cluster of
stars and millions of years back in time
American astronomer Edwin Hubble soon
discovered that other galaxies were
even further away he also confirmed an
observation that they were all moving
away from us at incredible speed
those farthest away were going the
fastest in other words our universe was
expanding as if we were caught up in a
huge explosion how do we know this I'll
explain with a more prosaic example when
you watch a car speed past sounding its
horn the pitch seems to change as it's
coming towards you the sound waves are
bunched up so the horn seems to have a
high pitch as it passes by the pitch
suddenly drops because now the sound
waves are being stretched out this is
called the Doppler effect just by
measuring the change in pitch an
observer can calculate the speed of the
car and whether it's coming towards him
or moving away we can do the same with
stars and galaxies using light instead
of sound if a galaxy is moving away the
spectral lines will shift towards the
red end of the spectrum the opposite
happens if a galaxy is coming closer
they move towards the blue end so
cosmologists could not only calculate
which direction the galaxies are moving
but also their speed if we reverse the
course of these galaxies and wind the
film back space itself contracts back to
a single point just under 14 billion
years ago the start of this expansion is
called the Big Bang that's as far as
we've got so far in our understanding of
the scale and time span of the universe
research is now continuing to discover
what happened before the Big Bang now
let's come back to that sealed box to
the people who decided to skip the video
in order to speculate on the contents
have you figured out what's inside yet
of course not sitting in an armchair and
making wild guesses tells you nothing
you'll really know better off than the
Bronze Age farmers who looked up at the
stars and tried to guess what they were
just because the Big Bang is the current
extent of our knowledge doesn't mean
we've reached the end of the story every
time in history people thought they knew
the scale of the universe they've always
been proved wrong
to me the real story of the universe is
way more interesting than myths and
fairy tales for 100,000 years humans
have stared up at the same night sky and
wondered we are the first people in
human history not to wonder not to guess
but to know
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