Astronomy Place Learning Assistance

1. Don’t Panic • We are both learning how to use Astronomy Place. • Remember to “Join the Class” • There have been problems submitting answers • In the future I will set up Angel to accept answers in the cases where you can’t submit them to Astronomy Place • If problems persist come to my office so we can work together For this time deadline is extended until Monday

2. Spaceship EarthWhat are the motions of spaceship Eearth? • Earth SPINS on its axis towards the EASTonce every 24 hours • Earth ORBITS around the Sun once every 365.25 days. Speed ~ 1x105 km/hr. • Earth, the Sun & the Solar System all orbit around the center of the Milky Way galaxy once every 2.3x108 years. Speed ~ 8x105 km/hr. • The Milky Way is moving toward the Andromeda galaxy, speed ~ 3x105 km/hr • The Milky Way (along with the local group) partakes in the expansion of the universe.

3. Earth Spins (Rotates) on its axistoward the East, once every 24 hours

4. Earth ORBITS around the Sunonce a year What keeps the Earth in orbit and stops it from flying off?

5. The Solar System ORBITS the center of the Milky Way galaxy Period = 2.3x108 years What keeps it in orbit so it doesn’t fly off?

6. Our motion through the universeThe Milky Way is moving through the universe ~ 600 km/s

7. Expanding Universe Model - Balloon

8. The SeasonsWhat could produce our seasons - the difference between summer and winter? • Changing energy output by the Sun • Changing amount of energy we receive from the Sun • Distance from the Sun • Orientation of the ground re. Sun’s light (Tilt of Earth’s axis of rotation)

9. Sun’s heating & Distance

10. Sun’s heating & Orientation

11. Sun’s heating & Rays

12. The Cause of the Seasons

13. Why doesn’t Distance Matter? • Small variation for Earth — about 3% • Distance does matter for some other planets, notably Mars and Pluto. • Surprisingly, seasons are more extreme in N. hemisphere, even thought Earth is closer to Sun in S. hemisphere summer (and farther in S. hemisphere winter) because of land/ocean distribution

14. Moon’s Phases

15. Phases of the Moon

16. A Solar Eclipse

17. Eclipses • The Earth & Moon cast shadows. • When either passes through the other’s shadow, we have an eclipse. • Why don’t we have an eclipse every full & new Moon?

18. Planetary MotionUsually planets appear to move toward the East re the stars. Occasionally, they appear to move backward - toward the West, called Retrograde Motion

19. Retrograde MotionView from Earth: explained by big circles + epicycles big circle=‘deferent’. Explains most of planets motion Epicycle, rolls on big circle. Explains retrograde loop.

20. Retrograde Motion • Like the Sun, planets usually appear to move eastward relative to the stars. • But as we pass them by in our orbit, they move west relative to the stars for a few weeks or months. • Noticeable over many nights; on a single night, a planet rises in east and sets in west…

21. Next Week • I will be away Monday and Wednesday.Classes will occur in BPS 1410 as usual both days. Dr. Horace Smith will take over for me.

22. Assignment for Next Week Make sure you pick up homework dueWednesday Jan 28(If you miss a Wednesday class, homeworkis linked to the course web pagehttp://www.pa.msu.edu/courses/isp205/sec-3) • Pre-class assignment for Monday Jan 26, is linked to the course web page and is to be done on Angel.