What will I learn about: the staggering scale of the Cosmos, where Earth is just one of ten sextillion planets, offering a humbling perspective on our daily human struggles?

Understand the staggering scale of the Cosmos, where Earth is just one of ten sextillion planets, offering a humbling perspective on our daily human struggles.

What will I learn about: how the third-century BCE scholar Eratosthenes ingeniously proved the Earth was a sphere and calculated its circumference using nothing but the sun's shadows?

Discover how the third-century BCE scholar Eratosthenes ingeniously proved the Earth was a sphere and calculated its circumference using nothing but the sun's shadows.

What will I learn about: how our ancient nomadic ancestors utilized the predictable movements of the night sky to track seasons, navigate animal migrations, and survive?

Find out how our ancient nomadic ancestors utilized the predictable movements of the night sky to track seasons, navigate animal migrations, and survive.

What will I learn about: Trace humanity's evolving understanding of the solar system, from Ptolemy's Earth-centric theory to Johannes Kepler's groundbreaking discovery of elliptical orbits?

Trace humanity's evolving understanding of the solar system, from Ptolemy's Earth-centric theory to Johannes Kepler's groundbreaking discovery of elliptical orbits.

What will I learn about: Learn why Venus is a scorching, toxic hellscape fueled by an extreme greenhouse effect, and why Mars's Earth-like conditions make it a plausible target for future human habitation?

Learn why Venus is a scorching, toxic hellscape fueled by an extreme greenhouse effect, and why Mars's Earth-like conditions make it a plausible target for future human habitation.

Cosmos

One small step toward understanding the greatness of the universe

Carl Sagan

★ 4.4 / 5(312 ratings)

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Categories:

Science

If You're Curious About These Questions...

You should listen to this audiobook

💡Have you ever wondered how the entire history of our universe would look if it were condensed into a single calendar year?
💡Did you know that you are literally made of “star stuff,” and that your very existence is linked to the life cycles of distant suns?
💡Are you curious about how a single ancient library in Egypt paved the way for our modern journey into the vast cosmic ocean?

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Key Takeaways from Cosmos

✓Understand the staggering scale of the Cosmos, where Earth is just one of ten sextillion planets, offering a humbling perspective on our daily human struggles.
✓Discover how the third-century BCE scholar Eratosthenes ingeniously proved the Earth was a sphere and calculated its circumference using nothing but the sun's shadows.
✓Find out how our ancient nomadic ancestors utilized the predictable movements of the night sky to track seasons, navigate animal migrations, and survive.
✓Trace humanity's evolving understanding of the solar system, from Ptolemy's Earth-centric theory to Johannes Kepler's groundbreaking discovery of elliptical orbits.
✓Learn why Venus is a scorching, toxic hellscape fueled by an extreme greenhouse effect, and why Mars's Earth-like conditions make it a plausible target for future human habitation.

Learning Tools

Reinforce what you learned from Cosmos

Mind Map

Cosmos

Scale of the Universe+

History of Astronomy+

Planetary Science+

Extraterrestrial Life+

Roots of Modern Science+

Physics of Light+

Space Exploration+

Quiz — Test Your Understanding

Question 1 of 8

How did Eratosthenes, the director of the Library of Alexandria, deduce that the earth was a curved sphere rather than flat?

A. By observing the phases of the moon during a lunar eclipse and noting the shape of the earth's shadow.
B. By comparing the lengths of shadows cast by sticks at midday in two different cities.
C. By sailing a ship out of the harbor and observing its mast disappear over the horizon.
D. By mapping the changing positions of constellations over a calendar year.

Question 2 of 8

Based on Tycho Brahe's data, Johannes Kepler calculated that planetary orbits are elliptical. What other major theory did Kepler propose that anticipated a later scientific breakthrough?

A. He suggested that the universe is constantly expanding based on the redshift of starlight.
B. He argued that the earth revolves around the sun, directly challenging Ptolemy's geocentric model.
C. He theorized that a force called 'magnetism' acted on bodies at a distance, anticipating Newton's theory of universal gravitation.
D. He proposed that light travels at a constant speed, laying the groundwork for Einstein's theory of relativity.

Question 3 of 8

According to the text, what primarily causes the extreme surface temperatures on Venus?

A. Its proximity to the sun combined with a complete lack of atmospheric cloud cover.
B. A runaway greenhouse effect caused by an atmosphere of 96 percent carbon dioxide and sulfuric acid clouds.
C. Constant volcanic activity that continuously releases magma across the planet's surface.
D. The high concentration of hydrogen and helium gas that traps cosmic radiation.

Question 4 of 8

If humans were to receive a message from an advanced extraterrestrial civilization, why would it most likely be transmitted via radio waves using a sequence of prime numbers?

A. Radio waves are the only waves capable of penetrating Earth's atmosphere, and prime numbers are the basis of all computer codes.
B. Radio is a fast, cheap method for long-distance communication, and prime numbers clearly indicate a deliberate message from an intelligent lifeform.
C. Radio waves are unaffected by the gravitational pull of black holes, and prime numbers map perfectly to the atomic structure of hydrogen.
D. Spacecraft like Voyager 1 only possess radio receivers, and prime numbers are required to bypass their security encryption.

Question 5 of 8

Why was Project Orion, a 1958 initiative to create an interstellar aircraft, ultimately abandoned?

A. Scientists realized that atmospheric pressure in space would cause the aircraft's water supply to boil away instantly.
B. The project required more plutonium than was available on Earth at the time.
C. A 1963 treaty between the United States and the Soviet Union banned the detonation of nuclear weapons in space, which the aircraft relied on for propulsion.
D. NASA decided to divert all of its funding into the Voyager missions instead.

Question 6 of 8

Despite their early scientific breakthroughs, the experimental approaches of the ancient Ionians were suppressed for centuries. What was the primary reason for this suppression?

A. The Library of Alexandria was destroyed, taking all written records of Ionian experiments with it.
B. The Ionians refused to share their findings with other Mediterranean cultures due to trade disputes.
C. Thinkers like Pythagoras and Plato popularized the idea that pure theoretical thought was divine, while physical experimentation was suitable only for slaves.
D. The Babylonians conquered Ionia and outlawed all scientific practices that contradicted the teachings of their god, Marduk.

Question 7 of 8

What fundamental rule about the universe did Albert Einstein illustrate through his 'thought experiments' (Gedankenexperimente) involving a moving car and a train?

A. The speed of light changes depending on the velocity of the observer.
B. Time passes more slowly for objects experiencing high gravitational fields.
C. Light always travels at the same constant speed, and nothing can travel faster than it.
D. The color of light shifts toward the red end of the spectrum as objects move away from an observer.

Question 8 of 8

What was the specific purpose of the gold-plated copper phonograph attached to the Voyager 1 and 2 spacecraft?

A. To serve as a redundant backup computer system in case the primary navigation systems failed in deep space.
B. To provide a curated representation of Earth's culture, languages, and biological data to any extraterrestrials who might intercept it.
C. To broadcast continuous radio and television advertisements to drown out confusing signals from Earth.
D. To record and store the astronomical data and photographs gathered as the spacecraft passed Jupiter and its moons.

Cosmos — Full Chapter Overview

1Recommendation
21 — Earth is remarkably tiny.
32 — The stars and planets have always beckoned, showing us Earth’s place in the universe.
43 — Venus is hellish and unwelcoming, but Mars might be habitable.
54 — Life may exist on other planets, but it probably won’t arrive on Earth in spacecraft.
65 — Modern science isn’t entirely modern: the ancient Ionians came first, but their work was suppressed for centuries.
76 — Light has a unique role in our universe.
87 — Voyagers 1 and 2 carry our civilization into space.
98 — Final summary

Cosmos Summary & Overview

Cosmos (1980) is a milestone in popular science. It shows us the basic concepts behind our understanding of the universe, what the planets and the stars look like and how our comprehension of them has changed and evolved.

Who Should Listen to Cosmos?

Humanities students unsure of what gets scientists going
Lovers of science fiction
Anyone who’s ever looked up at the sky

About the Author: Carl Sagan

Carl Sagan was an American astronomer, author and famous popularizer of science. He co-wrote and narrated the television series Cosmos: A Personal Voyage, which was based on his best-selling book. It won him several awards, including an Emmy for Outstanding Individual Achievement.

Cosmos

If You're Curious About These Questions...

Listen to Cosmos — Free Audiobook

Key Takeaways from Cosmos

Learning Tools

Mind Map

Quiz — Test Your Understanding

Cosmos — Full Chapter Overview

Cosmos Summary & Overview

Who Should Listen to Cosmos?

About the Author: Carl Sagan

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