Chapter 27 Notes

The Sun-Earth-Moon System

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

The Electromagnetic Spectrum

Telescopes

• A telescope’s purpose is not to magnify objects, but to collect and focus light.

• Visible light: – Refracting (lenses)– Reflecting (mirrors)

• Radio telescopes:

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

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

Exploring the Moon

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

Moon Map

Moon Map

• A “Mercator” map of the Moon

Formation of the Moon

• Impact Theory: Currently accepted theory based on the Moon’s geology and computer simulations

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

Moon Phases

• Waxing: getting larger

• Waning: getting smaller

• Crescent: less than ¼ size

• Gibbous: greater than ¼ size

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

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”

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?)

Lunar Eclipse

• Moon passes through Earth’s shadow• We see the Moon darkened• Only occurs during full moon phase