Intro to Space

4. Developed the Wheels on Wheels geocentric model and thought planets moved at a constant speed
6. Thought the Earth was the center of the universe because he observed the sun and stars rise in the east and fall in the west
9. First to see the moons of Jupiter through an improved telescope
11. The amount of matter that makes up an object
12. shape when the moon is less than half illuminated
13. Spinning on an axis; gives us day and night
14. shape when the moon in more than half illuminated but less than full
16. illuminated part of the moon is increasing
19. Modified the Wheels on wheels model to put the sun at the center

1. earth centered
2. sun centered
3. used to describe the movement around the sun (orbit)
5. Proposed 3 laws of planetary motion
7. force of attraction between any two objects
8. Marks the longest/ shortest day of the year
10. First to propose a heliocentric model and attempted to measure the distance of the earth, moon, and sun
15. Marks the time start of spring and fall/ equal amounts of daylight and nighttime hours
17. illuminated part of the moon is decreasing
18. The measure of the force of gravity on an object