1. Homework #2
degrees is how many degrees, arcminutes, and arcseconds?
How many degrees, arcminutes, and arcseconds does the moon move across the sky in one hour? (the lunar day is 24 hours and 48 minutes long)
The moons diameter is about 30 arcminutes, so find out how long it takes for the moon to travel its diameter.

2. The Daily Motion
As the Earth rotates, the sky appears to us to rotate in the opposite direction.
The sky appears to rotate around the N (or S) celestial poles.
If you are standing at the poles, nothing rises or sets.
If you are standing at the equator, everything rises & sets 90 to the horizon.

3. The Daily Motion The altitude of the celestial pole = [your latitude].
All stars at an angle < [your latitude] away from:
your celestial pole never set. (circumpolar)
the other celestial pole are never seen by you.
Other stars, (& Sun, Moon, planets) rise in East and set in West at an angle = [90  your latitude].

4. The Daily Motion daily circles --- CCW looking north, CW looking south
Höküpaÿa
Newa

5. Time Exposure Photograph:
• Estimate the exposure time • Which direction did stars move?

6. Gemini Telescope

7. Hawai`i
Chile

8. Time Exposure Photograph:
• Estimate the exposure time • Which direction did stars move? l

9. Time Exposure Photograph:
• Estimate the exposure time • Which direction did stars move?

10. Annual Motion
As the Earth orbits the Sun, the Sun appears to move eastward with respect to the stars.
The Sun circles the celestial sphere once every year.

11. Annual Motion ecliptic equinox solstice zodiac
the apparent path of the Sun through the sky
equinox
where the ecliptic intersects the celestial equator
solstice
where the ecliptic is farthest from the celestial equator
zodiac
the constellations which lie along the ecliptic

12. Annual Motion
The Earth’s axis is tilted 23.5° from being perpendicular to the ecliptic plane.
Therefore, the celestial equator is tilted 23.5° to the ecliptic.
As seen from Earth, the Sun spends 6 months north of the celestial equator and 6 months south of the celestial equator.

14. The Cause of the Seasons
Summer
Winter
Seasons are caused by the Earth’s axis tilt, not the distance from the Earth to the Sun!

15. The Cause of the Seasons

16. Seasonal Change in Sun’s Altitude
The “Figure 8” shows Sun at same time each day over a year.

17. When is summer?
The solstice which occurs around June 21 is considered the first day of summer.
It takes time for the more direct sunlight to heat up the land and water.
Therefore, July & August are typically hotter than June.

18. Why doesn’t orbital distance from the Sun matter?
Small variation for Earth — about 3% (but orbit distance does matter for some other planets, notably Mars and Pluto).
Surprisingly, seasons are more extreme in N. hemisphere, even though Earth is closer to Sun in S. hemisphere summer (and farther in S. hemisphere winter) — because of land/ocean distribution

19. Precession of the Equinoxes
The Earth’s axis precesses (wobbles) like a top, once about every 26,000 years.
Precession changes the positions in the sky of the celestial poles and the equinoxes.
Polaris won't always be the north star.
The spring equinox, seen by ancient Greeks in Aries, moves westward and is now in Pisces!

20. Phases of Moon
Half of the Moon is illuminated by the Sun and half is dark.
We see a changing combination of the bright and dark faces as the Moon orbits Earth.
You may want to do an in-class demonstration of phases by darkening the room, using a lamp to represent the Sun, and giving each student a Styrofoam ball to represent the Moon. If you lamp is bright enough, the students can remain in their seats and watch the phases as they move the ball around their heads.
How to Simulate Lunar Phases

21. Lunar Motion Phases of the Moon’s 29.5 day cycle waxing waning new
Muku
Külua
ÿOlekükahi
Huna
Hoku
Käloakükahi
Lono
new
crescent
first quarter
gibbous
full
last quarter
waxing
waning

22. hoÿonui Hilo Hoaka Kükahi Külua Küpau ÿOlekükahi ÿOlekülua Kükolu
ÿOlekükolu
ÿOleküpau

23. poepoe Huna Möhalu Hua Hoku MäheaIani Kulu Laÿaukükahi Laÿaukülua
Akua
Hoku
MäheaIani
Kulu
Laÿaukükahi
poepoe
Laÿaukülua
Laÿauküpau

24. ÿemi ÿOlekükahi ÿOlekülua ÿOleküpau Käloakükahi Käloakülua Käloapau
Käne
Lono
ÿemi
Mauli
Muku

25. We see only one side of the Moon
Synchronous rotation: The Moon rotates exactly once with each orbit.
This is why only one side is visible from Earth.
Use this tool from the Phases of the Moon tutorial to explain rise and set times for the Moon at various phases. As usual, please encourage your students to try the tutorial for themselves.

26. Thought Question First quarter Waxing gibbous Third quarter Half moon
It’s 9 A.M. You look up in the sky and see a moon with half its face bright and half dark. What phase is it?
First quarter
Waxing gibbous
Third quarter
Half moon
This will check whether students have grasped the key ideas about rise and set times.

27. Thought Question First quarter Waxing gibbous Third quarter Half moon
It’s 9 A.M. You look up in the sky and see a moon with half its face bright and half dark. What phase is it?
First quarter
Waxing gibbous
Third quarter
Half moon
If anyone chose “half moon,” remind them that there is no phase with that name… (and that first and third quarter refer to how far through the cycle of phases we are…)

28. What causes eclipses? The Earth and Moon cast shadows.
When either passes through the other’s shadow, we have an eclipse.
This slide starts our discussion of eclipses. Use the figure to explain the umbra/penumbra shadows.

29. Lunar Eclipse Lunar Eclipse
This interactive tool goes through lunar eclipses. Use it instead of or in addition to the earlier slides on eclipses.
Lunar Eclipse

30. Solar Eclipse Evolution of a Total Solar Eclipse
This interactive tool goes through the solar eclipses. Use it instead of or in addition to the earlier slides on eclipses.
Evolution of a Total Solar Eclipse

31. When can eclipses occur?
Lunar eclipses can occur only at full moon.
Lunar eclipses can be penumbral, partial, or total.
Use the interactive figure to show the conditions for the 3 types of lunar eclipse.

32. When can eclipses occur?
Solar eclipses can occur only at new moon.
Solar eclipses can be partial, total, or annular.
Use the interactive figure to show the conditions for the 3 types of solar eclipse.

33. Why don’t we have an eclipse at every new and full moon?
The Moon’s orbit is tilted 5° to ecliptic plane.
So we have about two eclipse seasons each year, with a lunar eclipse at new moon and solar eclipse at full moon.
Use this pond analogy to explain what we mean by nodes and how we get 2 eclipse seasons each year (roughly).
Note: You may wish to demonstrate the Moon’s orbit and eclipse conditions as follows. Keep a model “Sun” on a table in the center of the lecture area; have your left fist represent the Earth, and hold a ball in the other hand to represent the Moon. Then you can show how the Moon orbits your “fist” at an inclination to the ecliptic plane, explaining the meaning of the nodes. You can also show eclipse seasons by “doing” the Moon’s orbit (with fixed nodes) as you walk around your model Sun: the students will see that eclipses are possible only during two periods each year. If you then add in precession of the nodes, students can see why eclipse seasons occur slightly more often than every 6 months.

34. Summary: Two conditions must be met to have an eclipse:
It must be a full moon (for a lunar eclipse) or a new moon (for a solar eclipse).
AND
2. The Moon must be at or near one of the two points in its orbit where it crosses the ecliptic plane (its nodes).

35. Eclipse Predictions
Eclipses recur in the approx. 18 yr, 11 1/3 day saros cycle
But even then, eclipse location and type (e.g., partial, total) may vary

36. Photo by Olaf Menkens (1999 Mauna Loa)