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Feb 19, 1473
Nicolaus Copernicus
Copernicus proposed that the Sun, not the Earth, was the center of the universe or the solar system. He suggested that Earth rotates on its axis once daily and orbits the Sun annually His model correctly placed the planets in order from the Sun (Mercury, Venus, Earth, Mars, Jupiter, and Saturn) His heliocentric model naturally explained why planets appear to move backward (retrograde motion) in the sky at times. -
Dec 14, 1546
Tycho Brahe
He made the most accurate measurements of stars and planets without a telescope, which helped later astronomers figure out how planets move. He showed that comets were far away in space, not just in Earth's atmosphere, proving that the sky was bigger than people thought. He saw a new bright star appear in the sky (a supernova) and proved that the heavens could change, which went against what people believed at the time. -
Feb 15, 1564
Galileo Galilei
He discovered four large moons orbiting Jupiter (now called the Galilean moons. This proved that not everything orbits Earth. He discovered that the Milky Way was not just a cloudy band but actually made of countless stars. He observed dark spots on the Sun, proving it was not a perfect, unchanging object. He experimented with falling objects and discovered that all objects fall at the same rate regardless of weight (if there’s no air resistance). -
Dec 27, 1571
Johannes Kepler
He discovered that planets move in elliptical orbits (not perfect circles) around the Sun. He formulated three laws: -First Law: Planets orbit the Sun in ellipses, not circles. -Second Law: A planet moves faster when it’s closer to the Sun and slower when it’s farther away. -Third Law: The farther a planet is from the Sun, the longer it takes to orbit. -
William Herschel
He found Uranus, the first planet discovered with a telescope, proving that the solar system was bigger than people thought. He discovered that heat comes from light beyond what our eyes can see, which led to the study of infrared radiation. He mapped thousands of stars and figured out that the Milky Way is a huge, flat disk of stars. He discovered two moons of Uranus He discovered two moons of Saturn -
Maria Mitchell
She discovered a comet (now known as "Miss Mitchell's Comet") using a telescope, making her the first American woman to discover a comet. She became a professor at Vassar College, where she taught and encouraged many women to pursue careers in science, especially astronomy. She studied the motions of planets and stars, contributing to our understanding of how they move across the sky. -
Annie Jump Cannon
She developed a system for classifying stars based on their temperature and spectrum. She classified over 350,000 stars, more than anyone before her. Her success opened doors for other women to contribute to scientific research. -
Henrietta Swan Leavitt
She cataloged and studied over 2,400 Cepheid variable stars. She discovered that the brightness of certain types of variable stars is related to how long their brightness cycle takes. -
Edwin Hubble
He discovered that galaxies are moving away from us, and the farther a galaxy is, the faster it moves. This led to the realization that the universe is expanding. He showed that the Milky Way is just one galaxy among many and that other "nebulae" in the sky were actually entire galaxies far beyond the Milky Way. He helped determine the scale of the universe by measuring the distances to galaxies, which had previously been unknown. -
Carl Sagan
He helped discover that Venus has a thick, toxic atmosphere made mostly of carbon dioxide. He was one of the first scientists to advocate seriously for the search for life beyond Earth. He studied the atmospheres of other planets, including Mars and Jupiter, contributing to our understanding of their climates, weather patterns, and seasonal changes.