GE 150 Astronomy

1. GE 150 Astronomy Week #3 January 28, 30 2014

2. Path of the Sun Seasons: Conclusion

3. Complete this statement! When the noontime Sun is ____________________________ it’s summer; and when the noontime Sun is ____________________________ it is winter?

4. Which of these are true and which are false statements about the causes of the seasons and what evidence is there to support your answer? Earth is closer to the Sun in summer than in winter. During the summer, the Sun is giving off more energy and when it is winter the Sun is giving off less energy. When it is summer, more sunlight reaches Earth than it does during the winter.

5. Seasons Animation • Note that the Earth’s rotational axis is tilted relative to the Earth’s orbit and how much directsunlight shines on the northern and southern hemispheresthroughout a year. • How is this related to the seasons?

6. Tilted 23.5 degrees from vertical

8. Number of Daylight Hours Not to scale! 67°N 27°N Equator 27°S 67°N

9. The Reasons for the Seasons • The tilt of the Earth’s axis is the cause for the seasonal changes – it contributes two major effects

10. The Reasons for the Seasons: 1 The light from the Sun strikes the ground more directly in the Summer than in the Winter thus concentrating more of the Sun’s energy.

11. The Reasons for the Seasons: 2 The Sun spends more time above the horizon in the Summer than Winter resulting in longer days with more hours for heating

12. When the Sun is high in the sky during the day, the number of daylight hours is greater and the amount of direct sunlight received is greater. This results in Summer. Note how little the ‘beam’ of light is spread out in Summer

13. When the Sun is low in the sky during the day, the number of daylight hours is less and the amount of direct sunlight received is less. This results in Winter. Note how much more the ‘beam’ of light is spread out in Winter

14. Lunar Phases

15. How are the motions and positions of Earth and the Sun connected to what happens on Earth? Earth’s rotation on its axis determines the length of the day. Earth’s orbit around the Sun determines the length of the year. The tilt of Earth’s rotational axis with respect to the plane of Earth’s orbit causes the seasons.

16. The changing phases of the Moon originally inspired the concept of the month

17. Names of Moon Phase • New Moon • Waxing Crescent • First Quarter • Waxing Gibbous • Full Moon • Waning Gibbous • Third Quarter • Waning Crescent

19. Let’s put it in motion! Pay attention to where the Moon, Sun and Earth are located and how the Moon appears from Earth at each of these positions. Look at how much of the Moon is illuminated when at each position. Look at which side of the Moon is illuminated when at each position.

21. Phases of the Moon Although the Moon is always ½ lit by the Sun, we see different amounts of the lit portion from Earth depending on where the Moon is located in its orbit.

22. Phases of the Moon Although the Moon is always ½ lit by the Sun, we see different amounts of the lit portion from Earth depending on where the Moon is located in its orbit.