1 - History of Our Universe Part 1 (for schools)

Summary

This 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

00:00

🌌 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.

05:01

🔭 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.

Keywords

💡Observation

Observation is the act of watching or noticing specific details about something. In the context of the video, observation is a fundamental method used by scientists to gather data about celestial bodies without interfering with them. It is crucial for understanding the universe as it allows scientists to record and analyze the positions, movements, and other characteristics of stars and galaxies. For instance, the video mentions how the observation of planets with erratic orbits led to the development of more accurate models of the solar system.

💡Measurement

Measurement is the process of determining the size, amount, or degree of something through a quantitative process. The video emphasizes the importance of measurement in astronomy for determining distances and sizes of celestial objects. For example, Eratosthenes measured the Earth's diameter by observing the shadow cast by the sun at different locations, and later, the distances to stars were measured using triangulation, which required precise angle measurements.

💡Calculation

Calculation refers to the process of using mathematical methods to determine a result or solution. In the video, calculations are used to interpret the data gathered through observation and measurement. Johannes Kepler's calculations of planetary orbits are highlighted as a key example, where he used mathematical laws to describe the motion of planets, which helped to refine our understanding of the solar system.

💡Triangulation

Triangulation is a surveying method used to determine the distance to an object by measuring angles to it from two different known points. The video explains how this technique is applied in astronomy to measure the distances to stars. The principle is illustrated by the example of 61 Cygni, where the distance was calculated by observing the star from two different points on Earth's orbit around the Sun.

💡Spectroscopic Analysis

Spectroscopic analysis is the study of the interaction between matter and electromagnetic radiation through the use of a spectroscope. The video mentions how this technique is used to identify the composition of stars by analyzing the spectral lines of light they emit. For example, the discovery of helium on the Sun was made through observing its unique spectral lines, which were not matched by any known elements at the time.

💡Supernova

A supernova is a powerful and luminous explosion of a star, which outshines an entire galaxy for a short period. In the video, a supernova's explosion is used as a method to measure distances in space. The light from a supernova in 1987 was seen to reflect off a distant gas cloud, and by knowing the speed of light and the time it took to reach the cloud, astronomers could calculate the distance to the supernova, providing further evidence of the vast scale of the universe.

💡Doppler Effect

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. The video uses the analogy of a car's horn to explain how the Doppler effect can be observed in light waves to determine the motion of galaxies. If a galaxy's light shifts towards the red end of the spectrum, it indicates that the galaxy is moving away from us, which was a key observation that led to the understanding of the expanding universe.

💡Big Bang

The Big Bang is the prevailing cosmological model that explains the origin of the universe as a single, extremely hot and dense point that expanded rapidly. The video discusses how observations of the universe's expansion, combined with the Doppler effect, led to the theory of the Big Bang. It is presented as the current understanding of the universe's beginning, marking a significant milestone in our knowledge of cosmic history.

💡Helium

Helium is a chemical element with the symbol He and atomic number 2. It is a colorless, odorless, tasteless, non-toxic, inert, monatomic gas. In the video, helium is highlighted as an element first discovered in the Sun's spectrum before being found on Earth. This discovery was significant as it demonstrated that stars are composed of elements that can be analyzed through spectroscopic analysis, contributing to our understanding of stellar composition.

💡Cosmology

Cosmology is the study of the origin, evolution, and eventual fate of the universe. The video's narrative is deeply rooted in cosmology, as it explores the scientific methods and discoveries that have shaped our current understanding of the universe's scale, age, and composition. Cosmologists use a combination of observation, measurement, and theoretical models to piece together the history and structure of the cosmos.

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