1. NATS 1311 - From the Cosmos to Earth Our first exam will be next Tuesday, September 23 at the regular class time. We will have a review Thursday (Sept. 18) - at a time to be determined in class today - in the room next to where the regular lab is held. The exams will cover everything that we have covered in class up to the end of class Thursday.

2. NATS 1311 - From the Cosmos to Earth Eclipses The Earth & Moon cast shadows. When either passes through the other’s shadow, we have an eclipse Solar eclipse - when Earth passes through Moon’s shadow - occurs at new Moon Lunar eclipse - When Moon passes through Earth’s shadow - occurs at full Moon

3. NATS 1311 - From the Cosmos to Earth Causes of Eclipses Animation

4. NATS 1311 - From the Cosmos to Earth Why don’t we have eclipses every new and full Moon? Eclipses Twice A Month? Animation

5. NATS 1311 - From the Cosmos to Earth Moon’s Orbital Tilt Animation

6. NATS 1311 - From the Cosmos to Earth Moon’s orbit tilted 5° to ecliptic plane - Crosses ecliptic plane only at the two nodes - Eclipse possible only when full/new occur near nodes

7. NATS 1311 - From the Cosmos to Earth Imagine ecliptic plane as surface of pond - points at which Moon’s orbit crosses the surface are nodes. Eclipses only occur at nodes when the Moon is new or full.

8. NATS 1311 - From the Cosmos to Earth The shadow cast by an object in sunlight. Two distinct regions - sunlight is fully blocked in the umbra and partially blocked in the penumbra. Umbral shadow totally dark, penumbral shadow only slightly darker than no shadow. Shadows

9. NATS 1311 - From the Cosmos to Earth Types of Lunar Eclipses Total Moon in Earth’s umbra - maximum duration in total eclipse region - 140 minutes Partial Moon partly in Earth’s umbra Penumbra Moon in Earth’s penumbra - virtually undetectable

10. NATS 1311 - From the Cosmos to Earth As viewed from Earth, Earth's shadow can be imagined as two concentric circles. - type of lunar eclipse is defined by the path taken by the Moon as it passes through Earth's shadow.

11. NATS 1311 - From the Cosmos to Earth Generally two lunar eclipses per year, separated by 6 synodic months (177 days) - one on ascending node and one on descending node Descending node Ascending node

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13. Lunar Eclipses Animation

14. NATS 1311 - From the Cosmos to Earth Evolution of Total Lunar Eclipse Animation

15. NATS 1311 - From the Cosmos to Earth Lunar eclipse sequence.

16. NATS 1311 - From the Cosmos to Earth Total Lunar Eclipse The reddish color is because the Earth’s atmosphere bends some of the red light from the Sun around the Earth to the Moon.

17. NATS 1311 - From the Cosmos to Earth..

18. Total Lunar Eclipses Present - 2015 December 21, 2010 June 15, 2011 December 10, 2011 April 15, 2014 October 8, 2014 April 4, 2015 September 28, 2015 There are typically 2 partial or total lunar eclipses per year.

19. NATS 1311 - From the Cosmos to Earth Solar Eclipses We are fortunate - the Sun appears approximately as large in the sky (same angular diameter ~ 0.5 0 ) as the Moon.  When the Moon passes in front of the Sun, the Moon can cover the Sun completely, causing a total solar eclipse.

20. NATS 1311 - From the Cosmos to Earth Types of Solar Eclipses Total If the eclipse occurs when the Moon is close to the Earth - umbra covers small area of Earth’s surface (no more than 270 km in diameter) - anyone in this area sees a total eclipse. Partial Anybody in penumbral shadow (about 7000 km in diameter) will see a partial eclipse. Annular If the eclipse occurs when the Moon is far from the Earth - the umbra does not reach the Earth, only the penumbra. Anyone in this area directly behind the umbra sees an annular eclipse

21. NATS 1311 - From the Cosmos to Earth Evolution of a Partial Solar Eclipse Animation

22. NATS 1311 - From the Cosmos to Earth Evolution of a Total Solar Eclipse Animation

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24. Earth and Moon’s Orbits Are Slightly Elliptical Sun Earth Moon (Eccentricities greatly exaggerated!) Perihelion = position closest to the sun Aphelion = position furthest away from the sun Perigee = position closest to Earth Apogee = position furthest away from Earth

25. NATS 1311 - From the Cosmos to Earth Annular Solar Eclipses The angular sizes of the moon and the sun vary, depending on their distance from Earth. When Earth is near perihelion, and the moon is near apogee, we see an annular solar eclipse. Perigee Apogee Perihelion Aphelion

26. NATS 1311 - From the Cosmos to Earth So eclipses should be easy to predict - every six months at nodes when Moon crosses the ecliptic. However, the Moon’s orbit also precesses making prediction difficult. Moon’s Orbital Precession Animation

27. NATS 1311 - From the Cosmos to Earth Predicting Eclipses Solar eclipses are one of the most awe-inspiring events in human history - difficult for ancients to predict because of orbital precession and narrow region of occurrence. First predicted historical solar eclipse date precisely known - May 28, 585 BC. Opposing armies in Turkey massing for battle - eclipse frightened them so much, they put down their weapons and signed a treaty. Combination of changing dates of eclipse seasons (Lunar orbital precession), 29 1/2-day cycle of lunar phases, and period between lunar perigees --> solar eclipses occur in 18 year, 11 1/3 day cycle - saros cycle.

28. NATS 1311 - From the Cosmos to Earth Eclipses repeat - after one saros cycle, Moon and nodes of its orbit (and its perigee) return to same place with respect to the Sun - one saros contains 223 lunar months - changes location on Earth because of the extra 1/3 day - moves 8 hours of longitude west of the previous eclipse - repeats in same location after 3 saros cycles Saros Cycle

29. NATS 1311 - From the Cosmos to Earth Paths of Total Solar Eclipses Paths of same color represent successive saros cycles.

30. NATS 1311 - From the Cosmos to Earth Partial solar eclipses.

31. NATS 1311 - From the Cosmos to Earth Shadows from partial solar eclipses.

32. NATS 1311 - From the Cosmos to Earth Annular eclipses.

33. NATS 1311 - From the Cosmos to Earth Total solar eclipses.

34. NATS 1311 - From the Cosmos to Earth Total solar eclipse sequences.

35. NATS 1311 - From the Cosmos to Earth Total solar eclipses.

36. NATS 1311 - From the Cosmos to Earth Baily’s beads.

37. NATS 1311 - From the Cosmos to Earth Solar eclipse--the Moon’s shadow seen from space.

38. NATS 1311 - From the Cosmos to Earth Antikythera mechanism.

39. NATS 1311 - From the Cosmos to Earth Einstein’s eclipse.

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