1. Gravity and the Solar System
8th Grade
Space Science (Module G) U2L2

2. A few definitions - Gravity – force of attraction between objects
Orbit – path a body follows as it travels around another body in space
Aphelion – point of an object’s orbit farthest from the sun
Perihelion – point of an object’s orbit closest to the sun
Fun fact – if you are taking about an orbit around the Earth, it’s called apogee and perigee!

3. Nicolaus Copernicus (1473-1543)
Johannes Kepler ( )
Came up with the idea of a heliocentric model instead of a geocentric one
Discovered that orbits of planets are elliptical not circular.

4. Kepler’s laws of planetary motion (not necessary for your notes, just cool to know)
1. Each planet orbits the sun in an ellipse with the sun at one focus.

5. Planets move faster at perihelion (closest to the sun) than aphelion (farthest from sun).
2. As a planet moves around the sun, it sweeps out equal areas in equal times.

6. 3. The square of the orbital period (time it takes planet to go around sun) is proportional to the cube of the planet’s average distance from the sun
What you need to know: there is a direct relationship between the distance from the sun and the time it takes to go around it.

7. Law of Universal Gravitation
Developed by Isaac Newton in 1687
Says all objects in universe attract each other through gravitational force
Note: gravity is actually a pretty weak force. Magnetism is stronger
More mass = more gravity
The strength of the gravitational force depends on the product of the masses
More distance = less gravity
The strength of the gravitational force is inversely proportional to the square of the distance
Newtons Universal Law of Gravitation - Science in a Minute -

8. Centripetal force - Inward force that causes an object to move in a circular path
Object on string: string is “inward force”
Planets around stars: gravity is “inward force”

9. THE FORMATION OF THE SOLAR SYSTEM!
4.6 billion years ago – solar nebula (cloud of dust and gas) collapsed
-in nebula, inward pull of gravity is balanced by outward push of gas pressure in cloud
-some outside force, maybe explosion of nearby star, started nebular collapse
2. Gravity pulled mass toward center
-nebula contracted, began to rotate
-rotation sped up, nebula flatted into disk a.k.a. protostellar disk – our sun formed here!
-friction of collapse heated center to millions of degrees, starting fusion of hydrogen into helium
*this fusion caused explosions that balanced force of gravity

10. 3. As sun formed, dust grains collided and formed dust granules
Dust granules increased in size to a meter or so
Collisions between these bodies formed larger bodies – planetesimals – from which planets formed
Protostellar disk became protoplanetary disk in which planets formed
CCHistory Solar System - Start at 4:27 to see planets crashing into each other to form bigger ones end at 6:29
Next year – maybe use this article instead -

11. 4. Inner part of protoplanetary disk so hot that only rocks and metals were in solid form
Inner planets are called terrestrial planets & are made of rock and metal
Outer part of protoplanetary disk cooler, outer planets have rocky cores but captured ice and gasses with gravity
Outer planets are called gas giants & have rocky or metallic cores with deep atmospheres of gas and ice

12. Video - Birth of the Solar System #1. - http://www. youtube. com/watch
Video – Birth of the Solar System #3 - WATCH THIS! Just images, no words. -

13. Our solar system
Earth is part of a solar system – a collection of large and small bodies that orbit the sun
Terrestrial planets – Mercury, Venus, Earth, Mars
Rocky, dense, relatively small
Gas giant planets – Jupiter, Saturn, Uranus, Neptune
Thick, gaseous atmosphere, rocky core, HUGE volume
Moons – orbit planets
Comets
Asteroids
Main belt (btw/Mars & Jupiter)
Kuiper Belt (beyond Neptune)
And others!
Meteoroids
This is also from U1L1 – Structure of Universe & U2L6 Small Bodies in SS
ESS1A - The Universe and its Stars -

14. https://upload. wikimedia

15. The Milky Way & other galaxies
Galaxy – large collection of stars, gas & dust held together by gravity
Contain 100 million – 100 billion stars that orbit the center of the galaxy
The Universe
Space and all the matter and energy in it
Galaxies tend to form clusters and superclusters
Between the clusters are voids, where no matter exists

16. L4 – The Terrestrial Planets
For each planet, draw a picture on the front and on the inside write these things:
Diameter and comparison to Earth
Density & comparison to Earth
# of moons
Order from the sun (first, second, etc.)
Distance from the Sun in AU (astronomical unit)
Composition
2 other interesting facts

17. Diameter and comparison to Earth
Density & comparison to Earth
# of moons
Order
Distance from the Sun
Composition
2 other interesting facts
Mercury
Venus
Earth
Mars

18. Diameter and comparison to Earth
Density & comparison to Earth
# of moons
Order
Distance from the Sun
Composition
2 other interesting facts
Mercury
Venus
Earth
Mars

19. L5 – The Gas Giants
For each planet, draw a picture on the front and on the inside write these things:
Diameter and comparison to Earth
Density & comparison to Earth
# of moons
Order from the sun (first, second, etc.)
Distance from the Sun in AU (astronomical unit)
Composition
2 other interesting facts

20. Diameter and comparison to Earth
Density & comparison to Earth
# of moons
Order
Distance from the Sun
Composition
2 other interesting facts
Jupiter
Saturn
Uranus
Neptune

21. Diameter and comparison to Earth
Density & comparison to Earth
# of moons
Order
Distance from the Sun
Composition
2 other interesting facts
Jupiter
Saturn
Uranus
Neptune