1. PTYS/ASTR 206Lunar Phases / Eclipses 1/25/07 Today: Moon Phases

2. PTYS/ASTR 206Lunar Phases / Eclipses 1/25/07 Announcements The first homework due now. –The next assignment is now posted due Tuesday, Feb. 6 Weekly preceptor-led study group –Every Monday 10:30AM-12:00Noon

3. PTYS/ASTR 206Lunar Phases / Eclipses 1/25/07 Today’s topics What causes moon phases? What is Earthshine? What causes eclipses?

4. PTYS/ASTR 206Lunar Phases / Eclipses 1/25/07 The Phases of the Moon Key Points: –The Moon, at any time, is ½ illuminated by the Sun. The sunlit side always faces the Sun. –The Moon orbits the Earth. As it does so, we see different fractions of the illuminated side.   Sunlight 

5. PTYS/ASTR 206Lunar Phases / Eclipses 1/25/07 Nomenclature The “Dark Side” of the Moon –This is the side that is not illuminated by the Sun. –Note that this side of the Moon often faces us (a New Moon, for instance) The “Far Side” of the Moon –This is the side of the Moon that is not facing the Earth –We never see this side from Earth. Note that the Dark Side and Far Side are NOT the same –except during a full moon ONLY

6. PTYS/ASTR 206Lunar Phases / Eclipses 1/25/07 The New Moon When the Moon is between the Earth and Sun – it is in the New Moon phase The New Moon rises at sunrise, sets at sunset, and is highest in the sky at noon (just like the Sun!) This is the best time to observe the stars in the night sky without the glare of the moon interfering – dark skies

7. PTYS/ASTR 206Lunar Phases / Eclipses 1/25/07 The New Moon is the only time that a solar eclipse can occur

8. PTYS/ASTR 206Lunar Phases / Eclipses 1/25/07 The Full Moon When the Moon is at opposition – i.e on the opposite side of the Sun, we see the fully illuminated side. This is the Full Moon phase The Full Moon rises at sunset, sets at sunrise (exactly opposite to the Sun) This is the worst time to observe the stars in the night sky because of the Moon’s glare –It is also not an ideal time to observe features on the moon through a telescope.

9. PTYS/ASTR 206Lunar Phases / Eclipses 1/25/07 The Full Moon phase is the only time in which a lunar eclipse can occur

10. PTYS/ASTR 206Lunar Phases / Eclipses 1/25/07 The First-Quarter Moon When we see half of the sunlit side of the Moon it is said to be a quarter moon. If this occurs before the Full Moon (and after the New Moon) – the phase is the First-Quarter Moon The First-Quarter Moon rises at noon, and sets at midnight. This is an excellent time to observe Moon features such as craters, rilles and rimae – it is best to look along the terminator (the separator between light and dark) –Go out shortly after sunset to get the best views (it is highest in the sky)

11. PTYS/ASTR 206Lunar Phases / Eclipses 1/25/07 The Third-Quarter Moon If a quarter-moon phase occurs after the Full Moon (and before the New Moon) – the phase is the Third-Quarter Moon The Third-Quarter Moon rises at midnight, and sets at noon. Just like the 1 st -quarter Moon, this is an excellent time to observe moon features though a telescope. –Go out just before sunrise (it is highest in the sky)

12. PTYS/ASTR 206Lunar Phases / Eclipses 1/25/07 Waxing and Waning phases Waxing (“increasing”) is the term used to describe the phases after the New Moon and before the Full Moon –During this phase, each day we see more and more of the illuminated side of the Moon –Includes the first-quarter phase –The beautiful crescent Moon seen just after sunset is in a “waxing” crescent phase Waning (“decreasing”) is the term used to describe the phases after the Full Moon and before the New Moon –During this phase, each day we see less and less of the illuminated side of the Moon –Includes the third-quarter phase –The crescent Moon seen just before sunrise is in a “waning” crescent phase This is an example of a “waxing” moon (it increases with time) May 3 May 1 April 29

13. PTYS/ASTR 206Lunar Phases / Eclipses 1/25/07 Gibbous and Crescent Gibbous means the “full”-ish phase which is when the Moon is between the 1 st and 3 rd quarter phases and we see more than half of the illuminated side of the Moon During the crescent phases we see less than half of the illuminated side of the Moon Gibbous Moon Crescent Moon

14. PTYS/ASTR 206Lunar Phases / Eclipses 1/25/07

15. PTYS/ASTR 206Lunar Phases / Eclipses 1/25/07 Order of the Moon Phases (1. - start) New Moon –dark skies ! –Moon is not visible (glare from the Sun) (2. - after a few days) –Waxing crescent –Sets shortly after sunset (3. - about 7 days) First Quarter Moon –Actually a 1/2 moon –Moon goes from a crescent to a “gibbous” moon (4. - about 14 days) Full Moon –Goes from waxing to waning (5. - about 21 days) Third- Quarter moon –Another ½ moon –Waning phase –Goes from gibbous to crescent (6. - about 26 days) –Waning crescent –Rises shortly before sunrise (1. - start again) New Moon

16. PTYS/ASTR 206Lunar Phases / Eclipses 1/25/07 What is a Blue Moon? Two definitions: (1) The second full moon within one calendar month (2) the 3 rd full moon in a season that has 4 full moons (huh?) –From the Farmer’s Alamanc! –The 4 th is the “Harvest Moon” It is NOT BLUE !!

17. PTYS/ASTR 206Lunar Phases / Eclipses 1/25/07 Today’s topics What causes moon phases? What is Earthshine? What causes eclipses?

18. PTYS/ASTR 206Lunar Phases / Eclipses 1/25/07 Earthshine Sunlit side of the Moon Dark side of the Moon, Illuminated by Earthshine

19. PTYS/ASTR 206Lunar Phases / Eclipses 1/25/07 Earthshine is due to the double reflection of sunlight. –Light from the Sun is reflected off of the Earth (point A) onto the Moon (point B). Some of this light is then reflected off of the Moon back towards the Earth (point C). The brightest part of the Moon is illuminated by the Sun and the rest is dimly illuminated by this doubly reflected light.

20. PTYS/ASTR 206Lunar Phases / Eclipses 1/25/07 Saturn’s moon Iapetus seen in “Saturnshine ”

21. PTYS/ASTR 206Lunar Phases / Eclipses 1/25/07 Today’s topics What causes moon phases? What is Earthshine? What causes eclipses?

22. PTYS/ASTR 206Lunar Phases / Eclipses 1/25/07 Eclipses Lunar Eclipses –This occurs when the Earth “shades” the Moon as it passes between the Moon and Sun –Total, Partial, Penumbral –Occurs only during a full moon Solar Eclipses –This occurs when the Moon passes in front of the Sun, blocking the Sun from view from Earth –Annular, Total –Occurs only during a new moon Lunar Eclipse of 10/27/04 photo by Instructor

23. PTYS/ASTR 206Lunar Phases / Eclipses 1/25/07 Lunar Eclipses Does the moon become invisible? –No, refraction of sunlight through the Earth’s atmosphere causes the moon to become reddish

24. PTYS/ASTR 206Lunar Phases / Eclipses 1/25/07 Lunar Eclipse

25. PTYS/ASTR 206Lunar Phases / Eclipses 1/25/07 Solar Eclipses

26. PTYS/ASTR 206Lunar Phases / Eclipses 1/25/07 Total solar eclipse

27. PTYS/ASTR 206Lunar Phases / Eclipses 1/25/07 Annular Solar Eclipse

28. PTYS/ASTR 206Lunar Phases / Eclipses 1/25/07 Eclipses occur only when the Sun and Moon are both on the line of nodes

29. PTYS/ASTR 206Lunar Phases / Eclipses 1/25/07 Geometry and Path of Totality

30. PTYS/ASTR 206Lunar Phases / Eclipses 1/25/07 Eclipse Paths

31. PTYS/ASTR 206Lunar Phases / Eclipses 1/25/07 Reading for next class Chapter 5 –pp. 90-114 (you can omit section 5-8)

32. PTYS/ASTR 206Lunar Phases / Eclipses 1/25/07 Extra slides

33. PTYS/ASTR 206Lunar Phases / Eclipses 1/25/07 Guiding questions/concepts What causes moon phases? What is Earthshine? What is the difference between the synodic and sidereal month? What causes eclipses?

34. PTYS/ASTR 206Lunar Phases / Eclipses 1/25/07 Guiding questions/concepts What causes moon phases? What is Earthshine? What is the difference between the synodic and sidereal month? What causes eclipses?

35. PTYS/ASTR 206Lunar Phases / Eclipses 1/25/07 Guiding questions/concepts What causes moon phases? What is Earthshine? What is the difference between the synodic and sidereal month? What causes eclipses?

36. PTYS/ASTR 206Lunar Phases / Eclipses 1/25/07 Time and the Moon Two types of months are used in describing the motion of the Moon. With respect to the stars, the Moon completes one orbit around the Earth in a sidereal month, averaging 27.32 days. The Moon completes one cycle of phases (one orbit around the Earth with respect to the Sun) in a synodic month, averaging 29.53 days.

37. PTYS/ASTR 206Lunar Phases / Eclipses 1/25/07 Guiding questions/concepts What causes moon phases? What is Earthshine? What is the difference between the synodic and sidereal month? What causes eclipses?