1. Ch 18.1 Astronomy-The Original Science Part 1 When you finish this section you will be able to 1. Identify the units of a calendar 2. Evaluate calendars from different ancient civilizations 3. Explain how our modern calendar developed. 4. Summarize how astronomy began in ancient cultures and developed into a modern science.

2. Ch 18.1 Astronomy-The Original Science Astronomy is the study of all physical objects beyond the Earth. Before astronomy became a science, people in ancient cultures used the seasonal cycles of celestial objects to make calendars and organize their lives. Over time, some people began to observe the sky for less practical reasons – mainly to understand Earth’s place in the universe. Today, astronomers all over the world are using new technologies to better understand the universe.

3. The Stars Keeping Time Calendars are based on movements of objects in the sky. A calendar is a system for organizing time within a single unit called a year. A year is the time required for the Earth to orbit the sun once. Within a year are smaller units of time called months. A month is roughly the amount of time required for the moon to orbit the Earth once. Within a month are even smaller units of time called days A day is the time required for the Earth to rotate once on its axis.

4. Ancient Calendars Ancient cultures based their calendars on different observations of the sky a) Ancient Mayan cultures had a very complex calendar system that linked cycles of the sun, the moon and Venus. b) Ancient Chinese cultures made calendars as early as the 14 th century B.C. (3600 years ago) based on the moons phases and positions in the sky Chinese star map

5. c) Ancient Egyptian cultures based their calendar on the sun, with twelve 30-day months and one 5-day month at the end ofthe year. d) Ancient Hebrew cultures based their calendar on the moon and the sun. The number of months in their calendar alternated each year between 12 and 13 months.

6. Toward a Modern Calendar The early Roman calendar had exactly 365 days in a year and 7 days a week, which worked well at first, but gradually started shifting away from their original positions in the year. It was then determined that there were 365.25 days in a year which was corrected every four years by adding one extra day to the fourth year.( this day was not taken away the next year) We call this fourth year with the extra day a leap year. This calendar was known as the Julian Calendar

7. In the Mid 1500s It was calculated that a year is only 365.242 days long * A new calendar was created called the Gregorian calendar * This calendar is very much like the Julian calendar but it does not keep the extra day. When this change was made Pope Gregory had to reduce the calendar by 90 days to get it back to 365 days Scientist estimate that this calendar will remain accurate for another 3000 years

8. Ch 18.1 Part 2 When you finish this section you will be able to 1. Identify the units of a calendar 2. Evaluate calendars from different ancient civilizations 3. Explain how our modern calendar developed. 4. Summarize how astronomy began in ancient cultures and developed into a modern science.

9. Early observers- The Beginnings of Astronomy Nabta: The earliest record of astronomical observation (6000 to7000 years ago) Stonehenge: Ancient rock structure in southern England used to follow the seasons.(3000B.C.) The Babylonian: 700 B.C. precisely tracked the positions of planets and the moon which enabled them to make an accurate calendar.

10. The Chinese: 1000B.C. could predict eclipses and had named 800 stars by 350 B.C. The Greeks: Were the first to make astronomy a science. They calculated the size of the Earth, moon and sun as well as their distances from each other The Maya: Used a complex system of mathematics and astronomy

11. The American Indians: Built huge Earth works to record the four seasons which include the Vernal Equinox and Summer Solstice. Ancient Arabs: Named many of the stars which still have Arabic names.

12. Early Astronomers Ptolemy: (Greece) - Said that the Earth was the center of the universe and that all objects revolved around it. Copernicus: (Poland) – Claimed that all objects in the solar system revolve around the sun. Tycho Brahe: (Denmark) – Used several large tools to observe the sky and took very accurate measurements of the planets motion. Believed in the Ptolemy veiw if the universe Johannes Kepler: (Denmark) – Took Brahe accurate measurements and developed new laws of planetary motion which supported Copernicus view of the solar system Galileo Galilei: (Italy) 1 st to use telescope and proved that planets are celestial bodies not just dots of light, Favored Copernicus view. Issac Newton: (England) Discovery of gravity and development on the laws of motion helped explain and prove Copernicus theory is correct.

13. Modern Astronomy Today computers and telescopes are linked together. Computers not only control telescopes, but they also process the information gathered by the telescopes so that astronomers may better analyze it. Better telescopes on earth and in space allow us to study objects both near and far.