Chapter 18.3AMSTI Lesson 2

Study Guide Answers

1. About how old is the Earth?

• The Earth is approximately 4.5 billion years old.

2. How was the moon created?

• The moon formed when a Mars-sized asteroid collided with Earth 100 million to 200 million years after Earth was formed. The debris from the collision was thrown out into space, and that debris eventually joined together to form the moon.

3. What is the Earth’s only natural satellite?

• The moon is Earth’s only natural satellite.

4. What would happen if the moon traveled too quickly? Too slowly?

• If the moon traveled too quickly, it would escape Earth’s gravity and zoom out into space.• If the moon traveled too slowly,

Earth’s gravity would pull it down to Earth.

5. Why do the sun and moon appear to be the same size?

• The sun and moon appear to be the same size because the sun is 400 times larger than the diameter of the moon. The sun is also 400 times farther away from Earth than the moon is.

6. Explain why we have leap year.

• It takes the Earth 365 ¼ days to orbit the Sun in one year. Since our calendar year is 365 days, we have an extra ¼ day every year to be accounted for. So every 4 years, we add an extra day (February 29) to our calendar.

7. What device uses a curved mirror to gather and focus light?

• A reflecting telescope uses a curved mirror to gather and focus light.

8. What device uses a set of lenses to gather and focus light?

• A refracting telescope uses a set of lenses to gather and focus light.

9. What are 2 disadvantages of using a refracting telescope?

• The lenses focus colors of light at slightly different distances, so images cannot be perfectly focused.• The size of the lens is limited. If the

lens is too large, the glass sags and images are distorted.

10. What are 3 advantages of reflecting telescopes?

• The mirrors can be very large.• The polished curved side of the

mirror does not let light enter the glass.• Mirrors allow all colors of light to be

focused at the same time.

11. Define altitude.

• Altitude is the angle between the object and the horizon.

12. Define zenith.

• Zenith is the imaginary point above an observer’s head. The zenith always has a 90 degree altitude.

13. What is the horizon?

• The horizon is the line where the sky and Earth appear to meet.

14. What are regions of the sky that have recognizable star patterns?

• These regions are called constellations. There are 88 constellations.

15. What device helps describe the location of a star or a planet?

• An astrolabe can help describe the location of a star or planet.

16. What are circumpolar stars?

• Circumpolar stars are stars that can be seen at all times of year and all times of night. They never set, and appear to circle the celestial poles.

17. What is the distance light travels in one year?

• A light-year is the distance that light can travel in one year.

18. What is the distance of a light-year?

• One light-year is equal to about 9.46 trillion kilometers.

19. What is red shift?

• Redshift happens when an object is quickly moving away from an observer, the light emitted looks redder than it normally does.

20. What is blue shift?

• Blue shift occurs when an object is moving quickly toward an observer, the light emitted from the object looks bluer than it normally does.