1. Lunar Eclipse
Chapter 3 from book

2. Objectives
To be able to describe the phenomenon of how a lunar eclipse occurs.
To be able to apply what they already know about the moons orbit to this “special case.”
To apply what they know about the wavelengths of light to the appearance of the moon during the eclipse.

3. Starter
Fall equinox on September 22 - Sunday

4. Lunar Eclipse http://www.youtube.com/watch?v=wuhNZejHeBg
This is a brief video from NASA explaining how a lunar eclipse works.

5. Lunar Eclipse
Take note of the components of Earth’s shadow, the umbra and penumbra and the role they play in the lunar eclipse

6. Lunar Eclipse
Moon is tipped only a few degrees from the plane of Earth’s orbit around the sun.
Earth’s shadow points directly away from the sun (also on the plane of Earth’s orbit)\
Thus a lunar eclipse is when the Moon’s path is carries it directly through the shadow of the Earth.

7. Umbra This is the region of total shadow From the book:
If you were drifting in your space suit in the umbra of Earth’s shadow, the sun would be completely hidden behind Earth.

8. Penumbra Again, if you are drifting in your space suit:
In the penumbra, you would see part of the sun peeking around the edge of Earth.
You would be in partial shadow.
Sunlight is dimmed but not “extinguished” like in the umbra.

9. At the Height of an Eclipse – in the Umbra

10. Lunar Eclipse
Generally most full moons pass north or south of Earth’s shadow and there is no eclipse.
There are partial eclipses and total eclipses.
Partial Eclipse – When the moon passes a bit too far north or south of Earth, it may only partially enter the umbra.
Usually cannot see the coppery glow.

11. Total Lunar Eclipse
During a total eclipse, the moon moves into the penumbra where it dims slightly.
As it moves, the dimming increases.
Finally it reaches the umbra where the moon begins to darken as it slides into the umbra.
When it is totally eclipsed, the moon does not disappear.

12. Total Lunar Eclipse
The moon does not receive direct sunlight but light waves in the red spectrum are bent around Earth.
They pass through the Earth’s atmosphere.
Blue light, much shorter wavelength, is scattered as it hits the atmosphere (which is why the sky is blue).
Red light continues on and does reach the moon, creating its reddish glow.

13. Total Lunar Eclipse
An eclipse can last for as much as 1 hour 45 minutes.
You Tube video of a “speeded up” lunar eclipse.

14. Review
Which lunar phases would be visible in the sky at dawn? At midnight?
Looking back at Earth from the moon, what phase would Earth have when the moon was full?
Could a solar-powered spacecraft generate any electricity while passing through Earth’s umbral shadow?
If a lunar eclipse occurred at midnight, where in the sky would you look to see it?