Early Astronomers

Tycho BraheGalileo Galilei

Johannes KeplerNicholas Copernicus

Edmund HalleySir Isaac Newton

Nicholas Copernicus

Polish – 1473-1543

• Concluded Earth was a planet• Developed the theory that Earth moves around the Sun

with the other planets. Model of the solar system with the Sun at the center

• He couldn’t prove his theory• Used circles to predict the orbits of the planets, so the

planets orbits strayed from predicted positions

Tycho Brahe

Danish 1546-1601

• Persuaded King Fredrick the II to build an observatory in Copenhagen before telescopes were invented (used his eyesight)

• Designed and built instruments (astrolabes and quadrants) to accurately measure locations of heavenly bodies.

• Observed a supernova (exploding star)• Observations, especially of Mars, were far more precise

than any previously made.

Galileo Galilei

Italian 1564-1642

• Made improvements to the telescope 3 times magnification to look at the moon, sun and planets out to Saturn

• Discovered the moon has mountains and craters, the Sun has sunspots, planets were circular discs, not points of light, Venus has phases like the moon and that 4 moons (satellites) orbit Jupiter

• Catholic church believed his theories went against the bible.

Johannes Kepler

German 1571-1630

• Discovered 3 laws of planetary motion using Brahe’s data of Mars while working as his assistant.

1. The path of each planet around the sun is an ellipse2. Planets travel more rapidly as they near the Sun and slow

as they become more distant3. Planets orbital period squared is equal to it’s mean solar

distance cubed (T2 = d3). Solar distances of planets can be calculated

Sir Isaac NewtonEnglish 1642-1727

• Used Kepler’s work to formulate and test the universal theory of gravity

Each one of every pair of bodies pulls on the other, the strength of the pull (gravity) depends on the amount of matter in the objects and the distance between them– This explained how planets and their moons could

remain in space while revolving around the Sun.

Edmund Halley

English 1656-1742

• Calculated the orbit of a comet observed in 1682 and proved it was the same comet observe in 1531 and 1607. Predicted the comet would again return in 1758.

• Mapped the stars of the southern hemisphere• Studied the Moon’s effect on tides• Measured the distance from Earth to the Sun• Convinced Sir Isaac Newton to publish his findings