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Aristarchus proposes a heliocentric model: 300 BC 

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Aristarchus proposes a heliocentric model: 300 BC 

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Aristarchus of Samos was the first to suggest that the Sun, not Earth, was at the center of the universe.

His model was not accepted at the time, but it influenced later scientists like Copernicus.

Mark, J. J., & Konstable. (2025). Aristarchus of Samos. World History Encyclopedia. https://www.worldhistory.org/Aristarchus_of_Samos/

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Hipparchus creates a star catalog: 129 BC

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Hipparchus creates a star catalog: 129 BC

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Hipparchus recorded the positions and brightness of about 850 stars.

He also discovered the precession of Earth’s axis

Grossman, L. (2022, November 7). Part of a lost, ancient star catalog has now been found. Science News. https://www.sciencenews.org/article/lost-ancient-star-catalog-found

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Ptolemy’s geocentric model in Almagest: 100 AD

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Ptolemy’s geocentric model in Almagest: 100 AD

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Ptolemy wrote a book describing a universe with Earth at the center.

His model explained planetary motion using circles within circles (epicycles) and was used for over 1,000 years.

Jones, & Raymond, A. (1998, July 20). Ptolemaic system | Definition & Facts. Encyclopedia Britannica. https://www.britannica.com/science/Ptolemaic-system

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Mayan astronomers created calendars and predicted eclipses accurately.

Indian astronomers like Aryabhata described Earth as rotating and calculated the size of the Moon.

Taub, B. (2023, October 13). How the ancient Maya were able to accurately predict eclipses. IFLScience. https://www.iflscience.com/how-the-ancient-maya-were-able-to-accurately-predict-eclipses-71113

Shastry, V. (2018, February 15). How Aryabhata got the earth's circumference right  Mint. https://www.livemint.com/Sundayapp/8wRiLexg1N2IOXjeK2BKcL/How-Aryabhata-got-the-earths-circumference-right-millenia-a.html

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Copernicus publishes On the Revolutions: 1543 

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Copernicus publishes On the Revolutions: 1543 

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Nicolaus Copernicus officially introduced the heliocentric model

His work marked the beginning of the Scientific Revolution.

Westman, & S, R. (2025, July 7). Nicolaus Copernicus | Biography, facts, nationality, discoveries, Accomplishments, & Theory. Encyclopedia Britannica. https://www.britannica.com/biography/Nicolaus-Copernicus

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 Galileo uses a telescope to observe space: 1610

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 Galileo uses a telescope to observe space: 1610

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Galileo discovered four moons orbiting Jupiter, showing not everything orbits Earth.

He also observed that the Moon has mountains and that Venus goes through phases.

Cermak, A. (2024, November 6). Galileo's Observations of the Moon, Jupiter, Venus and the Sun - NASA Science. NASA Science. https://science.nasa.gov/solar-system/galileos-observations-of-the-moon-jupiter-venus-and-the-sun/

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Sputnik 1 becomes the first satellite in space: 1957 

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Sputnik 1 becomes the first satellite in space: 1957 

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Launched by the Soviet Union, Sputnik 1 started the Space Race.

It orbited Earth and sent back simple radio signals.

Sputnik. (n.d.). https://www.nasa.gov/history/sputnik/index.html

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NASA astronauts Neil Armstrong and Buzz Aldrin became the first humans to walk on the Moon.

It was a major achievement for science and technology.

Apollo 11 - NASA. (n.d.). NASA. https://www.nasa.gov/mission/apollo-11/

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Voyager 1 and 2 were sent to explore the outer planets.

They are now the farthest human-made objects in space and still send back data.

Carney, S., & Carney, S. (2025, April 7). Fast Facts - NASA Science. NASA Science. https://science.nasa.gov/mission/voyager/fast-facts/

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Companies like SpaceX now launch rockets and send astronauts to space.

Space travel is becoming more commercial and more frequent.

O’Shea, C. A. (2025, July 15). Fourth NASA-Enabled private flight to space station completes safely - NASA. NASA. https://www.nasa.gov/humans-in-space/fourth-nasa-enabled-private-flight-to-space-station-completes-safely/