Chapter 18 Flashcards
Is the earth always the same distance away from the sun? When is it closest and farthest?
No. For the northern hemisphere, the distances are: Autumn - 150 million km Winter - 147 million km Spring - 149 million km Summer - 153 million km
Why is the moon’s gravitational mass weaker than the earth’s?
Because it has much less mass. Its gravitational force is only 1/6 of the earth’s.
Where did the moon come from?
Most people today believe the giant impact theory: 4.5 billion years ago, an object about the size of Mars collided with earth, breaking off a lot of earth’s material. That material formed the moon.
What three main features do you see on the surface of the moon?
- -craters (large, round pits formed by impacts from large space objects)
- -highlands - bright areas that are high in elevation
- -marias - dark areas that are low in elevation
picture on 427
What causes tides? how?
Tides (rising and falling levels of the oceans) are caused by the moon’s gravity. Water on earth slides in the direction of the part of the earth directly under the moon.
What are some astronomical cycles you might know?
- year - how long the earth takes to travel (revolve) around the sun
- day - how long the earth takes to rotate (spin) once
- month - how long the moon takes to revolve around the earth
How could you keep track of time using the sun?
plant a vertical tower in the ground (like a sundial or obelisk – picture on page 431) and keep track of where the shadow is positioned. Obelisks came first; then people developed sundials.
What is the lunar cycle?
the change in the appearance of the moon based on the positions of the earth, moon, and sun
What affects how the moon looks to us?
All we see when we look at the moon is the light that gets reflected from the sun. So if the moon is BETWEEN the earth and the sun, all of the sunlight that hits the moon gets reflected back at the sun, and we don’t see anything. But if the EARTH is between the moon and the sun, all of the sunlight that gets reflected off of the moon hits the earth and we see the whole thing as a full moon.
DIAGRAM ON PAGE 432. VERY IMPORTANT!
What are the eight phases of the moon?
Note: Waning = "getting smaller"; Waxing = "getting bigger"; Crescent = less than half waxing = more than half
New Moon Waxing Crescent First Quarter (half moon) Waxing gibbous Full moon (now it starts to get smaller) waning gibbous last quarter (half moon) waning crescent and then back to new moon
When does a lunar eclipse happen?
When earth’s shadow falls on the moon and completely covers it. Sun - earth - moon. See page 434 for picture.
When does a solar eclipse happen?
When the moon’s shadow falls on earth and blocks out the sun for a little while. Pictures on page 435.
Solar eclipses can be total or partial.
What causes the seasons?
The tilt of the earth’s axis causes the seasons. When part of the earth is farther away from the sun than another part of it, that part is in winter.
