Lunar Eclipse

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 • http://www.space.com/22852-fall-equinox-earth-seasons-explained.html • 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. • http://www.youtube.com/watch?v=lcRp1jKJmJU • 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?