Admin:

2. Admin: • Assignment 5 due now • No Assignment this week • First mid-term: Friday in class • Chapters 1-4 • Scientific calculators(exponents, cube root) and a 2B pencil with eraser are required. • Students with accommodations wishing to use the test center should go to the DSS website and fill in an exam request form. • Extra Office hours • Thurs 1PM-3PM

3. How should I prepare for the test? Some suggestions: • Preparation time! You should have started already. • Don’t (only) use this lecture. This is just a quick skim of some topics and example questions, not a study guide • Read the Chapters carefully, summarize them in your own notes, test your recall. Most of the points will not be on the math questions • Test yourself on concepts (What phase is the moon if it’s overhead at dawn? What causes an eclipse? How big is the Universe? How old is the Universe? How does the force of Gravity work? What causes tides? Etc, etc…) • Work through the cosmic calculations examples, and the assignments. Make sure you can do them without looking at the book or solution • Use the available resources: • Office hours Thursday 1-3 • Email, for specific questions • Masteringastronomy assignments and study resources

5. Example things you should know speed=distance/time momentum=massvelocity ang. mom.=massvelocity radius force=mass  acceleration E=mc2

6. Example math question For a binary star system at a distance of 10 light years from Earth, the two stars are observed to be separated by an angle of 1 arcsec. What is the physical size of their separation in km? 1 light year = c × 60 × 60 × 24 × 365 c = 3× 105 km/s 1 arcsec=1/60/60 degrees Answer= 4.6 × 108 km

7. Another Example math question You are an astronomer on planet Nearth, which orbits a distant star. It has recently been accepted that Nearth is spherical in shape, though no one knows its size. One day, while studying in the library of Alectown, you learn that on the equinox your sun is directly overhead in the city of Nyene, located 1300 km due south of you. On the equinox, you go outside in Alectown and observe that the altitude of your sun is 81 degrees .

8. You are an astronomer on planet Nearth, which orbits a distant star. It has recently been accepted that Nearth is spherical in shape, though no one knows its size. One day, while studying in the library of Alectown, you learn that on the equinox your sun is directly overhead in the city of Nyene, located 1300 km due south of you. On the equinox, you go outside in Alectown and observe that the altitude of your sun is 81 degrees . • Measurements: • Nyene to Alectown • distance ≈ 1300km • angle difference = 90°- 81° • angle difference = 9° • 9/360 = 1300/CN • CN = 1300 * 360/9 = 52000 = 5.2  104 km Alectown Sun Nyene

9. which of these are possible ?

10. Phases of the Moon: 29.5-day cycle new crescent first quarter gibbous full gibbous last quarter crescent } • waxing • Moon visible in afternoon/evening • Gets “fuller” and rises later each day } • waning • Moon visible in late night/morning • Gets “less” and sets later each day

11. Moon Rise/Set by Phase • The different phases also rise and set at different times: • At new moon, the moon is on the same side as the sun, and so is only in the sky during the day (rises at dawn, sets at dusk) • At full moon, the moon is opposite the sun, so it rises at sunset, culminates at midnight, and sets at dawn • First quarter rises at noon, culminates at 6pm, and sets at midnight • Last quarter rises at midnight, culminates at 6am, and sets at noon • Note: the moon spends as much time in the sky in daytime as at night!

12. Moon Rise/Set by Phase Time the Moon Rises and Sets for Different Phases

13. which of these are possible ?

15. Tides and Phases Size of tides depends on the phase of the Moon. Note spring tides means extreme high and low tides Tides

17. The sky varies with latitude but not longitude. Your latitude = altitude of the pole

20. What causes the seasons? Seasons depend on how Earth’s axis affects the directness of sunlight. Note - not because one hemisphere is closer to the sun!!!

22. Kepler’s Third Law Kepler's 3rd Law

23. 100 billion stars

24. Where do we sit?

25. How did we come to be?

26. Are we ever sitting still? Earth rotates on axis: > 1,000 km/hr Earth orbits Sun: > 100,000 km/hr Solar system moves among stars: ~ 70,000 km/hr Milky Way rotates: ~ 800,000 km/hr Milky Way moves in Local Group Universe expands

27. 100 billion stars Momentum=mv Ang Momentum=mvr

28. p2=a3

29. We see apparent retrograde motion when we pass by a planet in its orbit. Mars Retrograde Motion

30. How did Copernicus, Tycho, and Kepler challenge the Earth-centered idea? • Copernicus created a Sun-centered model; Tycho provided the data needed to improve this model; Kepler found a model that fit Tycho’s data. • Kepler’s three laws of planetary motion 1. The orbit of each planet is an ellipse with the Sun at one focus. 2. As a planet moves around its orbit it sweeps our equal areas in equal times. 3. More distant planets orbit the Sun at slower average speeds: p2 = a3. • Galileo solidified the Copernican revolution. • His experiments and observations overcame the remaining objections to the Sun-centered solar system.

31. Newton’s Three Laws of Motion • An object moves at constant velocity if no net force is acting. • Force = mass  acceleration. • For every force, there is an equal and opposite reaction force.

32. Conservation Laws • Conservation of momentum • Conservation of angular momentum • Conservation of energy