1. Intro to Astronomy
Grade 9 Science

2. Astronomy Intro Grade 9 Science
The universe is everything that exists, including all matter and energy everywhere.
The study of what is beyond Earth is called astronomy.

3. Astronomy Intro Grade 9 Science
History…
Geocentric Model
The geocentric model (earth centered model) was based on an ideas from Aristotle, but refined and finished by Claudius Ptolemy.
Ptolemy imagined that the solar system was made of perfect circles, but his model also had to explain retrograde motion. He did this by adding smaller perfect circles (epicycles) on the orbital paths of each planet (except for the sun).

4. Astronomy Intro Grade 9 Science
Heliocentric Model
Nicholas Copernicus with the help of Galileo proposed a model where the sun is the center of solar system. This model was not well received, but it did explain the retrograde motion better then Ptolemy’s model.
Johannes Kepler added to Copernicus’s by changing the orbital paths to elliptical instead of circular. This explained the speed changes they observed in the night sky.

5. Astronomy Intro Grade 9 Science
Origins of the Universe
There are a lot of models and ideas that exist to explain how the universe came about. The current accepted scientific model is called the Big Bang theory. Which states that the universe started from an infinitesimal point that exploded in a huge release of energy and matter 10 to 15 billion years ago.
The study of the origin and changes of the universe is called cosmology.

6. Astronomy Intro Grade 9 Science
Planets orbit the sun in elliptical orbits which are caused by gravitational forces. Orbital Period is the time it takes for one full orbit. Orbital period increases as the body gets closer to the sun. Along with orbiting, a planet also rotates about a central axis.

7. Astronomy Intro Grade 9 Science
Planets have two types of motion:
Rotation
Revolution
Effect of Earth’s Rotation
Rotation – the spinning of an object around its axis (an imaginary straight line joining the North Pole to the South Pole)
The Earth’s rotation around its axis takes 24 hours. The rotation causes day and night.

8. Astronomy Intro Grade 9 Science
Effect of Earth’s Revolution
Revolution – the movement of one object travelling around another.
It takes the Earth one year (365 days) to revolve around the Sun. This allows us to see different stars in different seasons.
The angle of the Earth’s axis in combination with its revolution cause our seasons.

9. Astronomy Intro Grade 9 Science
Seasons
Although the Earth’s distance from the Sun changes slightly as it orbits, the distance is not great enough to cause a substantial change in the climate.
The tilt of the Earth (23.5o) is what causes the seasons to change.
During the summer, the Northern Hemisphere is titled towards the Sun, while during the winter the Northern Hemisphere is titled away from the Sun.

10. Astronomy Intro Grade 9 Science
Each planet is unique in our solar system. Some of the differences are:
Surface temperature
Density
Combination of chemical elements
Gravitational field strength

12. Astronomy Intro Grade 9 Science
The Inner Planets (Terrestrial Planets)
1. Mercury
2. Venus
3. Earth
4. Mars
The Outer Planets (Gas Giants)
1. Jupiter
2. Saturn
3. Uranus
4. Neptune
5. Pluto (Dwarf Planet)

13. Mercury Diameter:4,878km Mass:0.0553EM Density:5.43 Gravity:0.284EG
Average Temperature:
400 to -170°C

14. Venus
Diameter:12,102km
Mass:0.8149EM
Density:5.25
Gravity:0.878EG
Average Temperature:500°C

15. Earth
Diameter:12,756km
Mass:  kg
Density:5.52
Gravity:9.8m/sec2
Average Temperature:15°C

16. Mars
Diameter:6,786km
Mass:0.1074EM
Density:3.95
Gravity:0.379EG
Average Temperature: -60°C

17. Jupiter
Diameter:142,984km
Mass: EM
Density:1.33
Gravity:2.4EG
Average Temperature: -140°C

18. Saturn
Diameter:120,536km
Mass:95.181EM
Density:0.69
Gravity:0.923EG
Average Temperature: °C

19. Uranus
Diameter:51,118km
Mass:14.531EM
Density:1.29
Gravity:0.793EG
Average Temperature: -214°C

20. Neptune
Diameter:49,528km
Mass:17,135EM
Density:1.64
Gravity:1.122EG
Average Temperature:-214°C

21. Astronomy Intro Grade 9 Science
Solar System
At the centre of our solar system is a star, the Sun, that is essential to life on Earth. The sun is the largest body in our solar system.

22. Astronomy Intro Grade 9 Science