astronomers

Astronomical observations have given us much more than the modern calendar that we use. The careful work of early astronomers helped people understand their place in the universe. The earliest astronomers had only oral histories to learn from. Almost everything they knew about the universe came from what they could discover with their eyes and minds. Not surprisingly, most early astronomers thought that the universe consisted of the sun, the moon, and the planets. They thought that the stars were at the edge of the universe. Claudius Ptolemy and Nicolaus Copernicus were two early scientists who influenced the way that people thought about the structure of the universe. 

Ptolemy  

In 140 CE, Ptolemy, a Greek astronomer, wrote a book that combined all of the ancient knowledge of astronomy that he could find. He expanded ancient theories with careful mathematical calculations in what was called the Ptolemaic theory. Ptolemy thought that the Earth was at the center of the universe and that the other planets and the sun revolved around the Earth. Although the Ptolemaic theory was incorrect, it predicted the motions of the planets better than any other theory at the time did. For over 1,500 years in Europe, the Ptolemaic theory was the most popular theory for the structure of the universe.

 

Copernicus: A Sun-Centered Universe

In 1543, a Polish astronomer named Copernicus published a new theory that would eventually revolutionize astronomy. According to his theory, the sun is at the center of the universe, and all of the planets—including the Earth—orbit the sun. Although Copernicus correctly thought that the planets orbit the sun, his theory did not replace the Ptolemaic theory immediately. When Copernicus’s theory was accepted, major changes in science and society called the Copernican revolution took place. 

 Tycho Brahe: A Wealth of Data

In the late-1500s, Danish astronomer Tycho Brahe (TIE koh BRAW uh) used several large tools, to make the most detailed astronomical observations that had been recorded so far. Brahe favored a theory of an Earth-centered universe that was different from the Ptolemaic theory. Brahe thought that the sun and the moon revolved around the Earth and that the other planets revolved around the sun. While his theory was not correct, Brahe recorded very precise observations of the planets and stars that helped future astronomers. 

 Johannes Kepler: Laws of Planetary Motion

 After Brahe died, his assistant, Johannes Kepler, continued Brahe’s work. Kepler did not agree with Brahe’s theory, but he recognized how valuable Brahe’s data were. In 1609, after analyzing the data, Kepler announced that all of the planets revolve around the sun in elliptical orbits and that the sun is not in the exact center of the orbits. Kepler also stated three laws of planetary motion. These laws are still used today.


 Galileo: Turning a Telescope to the Sky

In 1609, Galileo Galilei became one of the first people to use a telescope to observe objects in space. Galileo discovered craters and mountains on the Earth’s moon, four of Jupiter’s moons, sunspots on the sun, and the phases of Venus. These discoveries showed that the planets are not “wandering stars” but are physical bodies like the Earth. 

Isaac Newton: The Laws of Gravity 

 In 1687, a scientist named Sir Isaac Newton showed that all objects in the universe attract each other through gravitational force. The force of gravity depends on the mass of the objects and the distance between them. Newton’s law of gravity explained why all of the planets orbit the most massive object in the solar system—the sun. Thus, Newton helped explain the observations of the scientists who came before him.

Edwin Hubble: Beyond the Edge of the Milky Way 

Before the 1920s, many astronomers thought that our galaxy, the Milky Way, included every object in space. In 1924, Edwin Hubble proved that other galaxies existed beyond the edge of the Milky Way. His data confirmed the beliefs of some astronomers that the universe is much larger than our galaxy. Today, larger and better telescopes on the Earth and in space, new models of the universe, and spacecraft help astronomers study space. Computers, help process data and control the movement of telescopes. These tools have helped answer many questions about the universe. Yet new technology has presented questions that were unthinkable even 10 years ago. 

Neil Tyson

an astrophysisist 

explained what was happening in universe 

page Summary

 

Astronomy, the study of the universe, is one of the oldest sciences.

 


 
The units of the modern calendar—days, months, and years—are based on observations of objects in space
 

 Ptolemaic theory states that the Earth is at the center of the universe. 

 

 
Copernican theory states that the sun is at the center of the universe.
 
Modern astronomy has shown that there are billions of galaxies.