Astronomy – the Original Science

1. Pgs. 4 - 10 Astronomy – the Original Science

2. Astronomy • The study of all physical objects beyond Earth. • Astronomy has been studied for centuries before formal schooling began. • Cultures around the world would study the moon, sun and Earth and the stars in the sky. • They studied how these objects moved in the sky and told stories to explain their actions.

3. The Stars and Keeping Time • Ancient cultures learned seasonal movements of these objects as they moved across the sky and even based their calendars on this motion. • A calendar is a system for organizing time. • A year is the time required for the Earth to orbit the sun once. • A month is the amount of time required for the moon to orbit the Earth once. • A day is the time required for the Earth to rotate once on its axis.

4. Ancient Calendars • Ancient Mayan cultures had a complex system linking the sun, moon and Venus. • Ancient Egyptian cultures based their calendar on the sun with twelve 30 day months and one 5 day month. • Ancient Chinese cultures based their calendar on the moon’s phases and position in the sky. • Ancient Hebrew cultures based their calendar on the moon and sun. They had years that alternated 12 and 13 months.

5. Toward a Modern Calendar • The early Roman calendar had 365 days a year, however, the seasons slowly shifted and it was determined that there was 365.25 days a year. • Julius Caesar created the Julian calendar which included an extra day every four years, a leap year. • Pope Gregory XIII found a problem. • The year is actually 365.242 days. • He lowered the number of leap years and dropped 10 days from the calendar. • This is the Gregorian calendar and we use this calendar today.

6. Early Observers • Scientists have found evidence for astronomical activities all over the world. • They have recognized that there are numerous ancient groups that have observed these phenomena throughout time. • Some of these groups have even left behind the devices they used.

7. Nabta • In southern Egypt, a group of stones that are 6000-7000 years old are aligned with what would be the summer solstice. • The summer solstice occurs on the longest day of the year. • The site was probably used by cattle herder and used for trade, social bonding and rituals.

8. Stonehenge • Near Salisbury England is a group of stones arranged primarily in circles, known as stonehenge. • The stones are aligned with sunrise for summer and winter solstices. • Stonehenge was built about 1,500 – 3,000 b.c. • Stonehenge was most likely used as a place for ceremony and rituals, but the origin of it is still a mystery.

9. The Babylonians • The ancient Babylonians were an empire from 700 b.c. to about 50 a.d.. • They tracked the positions of the planets and the moon . • They could forecast the movement of these celestial bodies and made a fairly accurate calendar.

10. Ancient Chinese Cultures • Ancient Chinese cultures could predict eclipses. • An eclipse occurs when the sun, the moon, and the Earth line up in space. • They have named 800 stars by 350 b.c. • The Chinese have accurately predicted and tracked the motion of the stars and planets improving their knowledge of the sky.

11. The Ancient Greeks • Greeks used the sky to keep track of time. • Greek philosophers tried to understand the place of Earth and humans in the universe. • They used mathematics and logic. • Aristotle successfully explained the phases of the moon and eclipses. • He also argued that the Earth was a sphere.

12. Native Americans • The Maya were the most skilled observers of the sky in the Americas. • They built buildings so that they aligned with celestial bodies. • Also, the Maya had complex systems of mathematics to help them interpret and predict the motion of the celestial bodies.

13. Ancient Arabs • Ancient Arabs inherited much of their astronomy knowledge from the old Greek empire. • They used that knowledge to develop astronomy. • They created the astrolabe, algebra and the number system we use today.

14. Early Astronomers – Ptolemy • Claudius Ptolemy wrote a book on astronomy in 140 a.d. that included his theory. • The ptolemaic theory is the theory that the Earth is at the center of the universe with the sun and other planets rotating around it. • Ptolemy’s theory was accepted for more than 1500 years.

15. Nicolaus Copernicus • In 1543, Copernicus published a new theory in astronomy. • He theorized that the sun is the center of the universe and the planets, including Earth, orbit the sun. • Although correct, Copernicus’ theory was not accepted right away.

16. Tycho Brahe • Tycho used several large tools to observe the sky. • Tycho favored the Earth-centered theory. • He said that the other planets orbit the sun and the sun and moon orbit the Earth. • With his large tools, Tycho recorded very precise movements of the celestial bodies that were used by later astronomers.

17. Johannes Kepler • Johannes Kepler was Tycho’s assistant, and upon Tycho’s death, he inherited Tycho’s work. • Kepler used Tycho’s work to publish his own laws of planetary motion. • He said that planets orbit in elliptical orbits around the sun.

18. Galileo Galilei • In 1609, Galileo was the first to use a telescope to study the celestial bodies. • He found four moons orbiting Jupiter. • He found craters and mountains on the moon. • Galileo also discovered sunspots on the sun and the phases of Venus. • Galileo believed in the sun-centered universe theory.

19. Sir Isaac Newton • In 1687, Isaac Newton explained why planets orbit the sun and why moons orbit the planets. • He came up with the ideas of the force of gravity. • Newton also came up with three laws of motion that govern the motion of the celestial bodies and objects on Earth.

20. William Herschel • He discovered Uranus in 1781. • Uranus was discovered using mathematic equations. • Herschel also found small fuzzy patches in the sky and recorded their position.

21. Edwin Hubble • In 1923, Hubble used photography to discover that the fuzzy patches of sky were actually galaxies from far away. • This led to the idea that the Milky Way Galaxy is not our entire universe, but actually a small part of it. • Hubble also discovered that the universe is expanding.