1. The Sun-Earth-Moon System
Chapter 27 Notes
The Sun-Earth-Moon System

2. Tools of Astronomy
Astronomers study radiation (light) emitted or reflected by distant objects
Visible light, radio waves, X-rays, UV, infrared, microwaves, and gamma rays are all types of electromagnetic radiation (EMR)
All EMR travels at the speed of light
Different types of telescopes detect different types of EMR

3. The Electromagnetic Spectrum

4. Telescopes
A telescope’s purpose is not to magnify objects, but to collect and focus light.
Visible light:
Refracting (lenses)
Reflecting (mirrors)
Radio telescopes:

5. Space-based Telescopes
Earth’s atmosphere blocks some types of EMR can distort visible light; some telescopes are located above the atmosphere. Here are a few of them:
Hubble: visible light
Chandra: X-rays
Spitzer: Infrared

6. Space-Based Astronomy
Robotic spacecraft
Cassini (Saturn): 2005
Mars Reconnaissance Orbiter: 2006
New Horizons (Pluto): 2006
Human space flight
International Space Station
Spinoff technology
More than 1400 different NASA technologies passed on to commercial industries

7. Exploring the Moon

8. History of the Moon
The Moon is about the same age as the Earth (4.5 billion years old)
Interior: layered, but no tectonic activity
Surface:
Highlands: mountains
Maria: impact basins filled with lava
Rilles: valleys created by flowing lava

9. Moon Map

10. Moon Map
A “Mercator” map of the Moon

11. Formation of the Moon
Impact Theory: Currently accepted theory based on the Moon’s geology and computer simulations

12. Time is based on Astronomy
Day: one complete rotation (plus ~4minutes)
Year: one complete orbit around the Sun
Month: based on one cycle of lunar phases
Seasons: caused by Earth’s tilt
Solstices: summer and winter
Equinoxes: “equal night” spring and fall
Sun’s maximum height is called the zenith. The zenith varies depending on latitude and time of year

13. Moon Phases Waxing: getting larger Waning: getting smaller
Crescent: less than ¼ size
Gibbous: greater than ¼ size

14. Lunar month vs. sidereal month
It takes 27.3 days for the Moon to make one complete orbit around the Earth
It takes 29.5 days for the Moon to complete one cycle of phases

15. Synchronous orbit The same side of the Moon always faces the Earth
The Moon spins one time on its axis each time it goes around the Earth
There is no “dark side of the Moon”

16. Solar Eclipse Earth passes through Moon’s shadow
We see the Sun blocked
Only occurs during new moon phase (why not every new moon phase?)

17. Lunar Eclipse Moon passes through Earth’s shadow
We see the Moon darkened
Only occurs during full moon phase