1. Not all of the Earth is exposed to light at the same time
In this picture:
It’s daytime for the part of the Earth that faces the sun
It’s nighttime for the part of the Earth that is turned away from the sun.

2. Questions to think about:
Does the Earth stand straight up?
No, the Earth has an axis. This is an imaginary line running from the North to the South Pole.
The Earth’s axis is tilted 23º.
Why is it _______ in Montreal, while it is _________ in Beijing?
Right now, Montreal is on the part of the world that is facing the sun (daytime). Beijing is on the part of the world that is turned away from the sun (nighttime).

3. Questions to think about:
How long does it take the Earth to make one full turn on its axis?
It takes the Earth 1 day (24 hours) to make one full turn on itself.
This is called rotation.
If you looked down on the Earth from above, what direction does the Earth rotate in?
Counter-clockwise (the opposite direction of a clock)

4. The Earth doesn’t just rotate…
The Earth also moves around the sun. How long does it take to go around the sun once?
It takes the Earth 365 and ¼ days (1 year) to go around the sun. This is called revolution.
The Earth follows an elliptical path in outer space around the sun. This path is called an _________.
orbit

5. Review questions from last class
What is the difference between rotation and revolution?
Rotation involves an object spinning on itself (like the Earth spinning, causing day and night). Revolution is an object going in a circular path (like the Earth orbiting the sun).
23º
The Earth’s axis is tilted at an angle of _______

6. Montreal
What time of day is it in Montreal? What time of year is it in Montreal?
It’s daytime (more specifically, early morning), because this part of the Earth has just turned toward the sun’ light.
It’s summer because the Northern hemisphere is tilted toward the sun.

7. Montreal
What time of day is it in Montreal?
What time of year is it in Montreal?
It’s night time (more specifically early evening) because this part of the Earth has just turned away from the sun’s light.
It’s winter because the Northern hemisphere is tilted away from the sun.

8. Montreal
What time of day is it in Montreal?
What time of year is it in Montreal?
It’s daytime (probably early afternoon), because Montreal is turned almost completely toward the sun’s light.
It’s fall or spring because both the Northern hemisphere and southern hemisphere are receiving equal amounts of sunlight.

9. VERY IMPORTANT
On ________________, the Northern hemisphere experiences maximum exposure to the sun. At the same time, the southern hemisphere’s exposure to the sun is minimum. This is called the _______________.
June 21st
solstice
On ________________ or _________________, both the northern and southern hemisphere experience equal exposure to the sun. This is called the _______________.
March 21st
September 21st
equinox

10. VERY IMPORTANT June 21st (solstice) 1st day of summer
Date
Northern Hemisphere
Southern Hemisphere
June 21st (solstice)
1st day of summer
1st day of winter
1st day of winter
1st day of summer
December 21st (solstice)
1st day of spring
1st day of fall
March 21st (equinox)
1st day of fall
September 21st (equinox)
1st day of spring

11. What time of day was this picture taken?
2:00 A.M.
This is because in summer time, areas that are very far north don’t ever fully turn away from the sun’s light.
In summer, it never gets dark at the North Pole

12. What time of day was this picture taken?
1 P.M.
This is because in winter time, areas that are very far north are fully turned away from the sun’s light.
In winter, the North Pole is in complete darkness.

13. Earth
Moon
Sun

14. The Moon
How long does it take for the moon to revolve around the Earth?
Approximately 1 month
Does the moon emit its own light?
No, the moon is not luminous. It only reflects sunlight. The shape of the moon we see depends on its position in its orbit around the Earth.

15. Full Moon
Waning gibbous
Waxing gibbous
Last quarter
1st quarter
Waning crescent
Waxing crescent
New moon