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The Moon

Its physical properties and relationship to Earth

Part 1

Solar Flares• https://www.youtube.com/watch?v=HFT7ATL

QQx8• https://www.youtube.com/watch?v=GrnGi-q6

iWc• As we are ending our unit on the sky, I found a

couple of videos from NASA showing a solar flare.

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Objectives

• To be able to describe the physical properties of the Moon.

• To be able to compare and contrast the Moon’s physical properties with those of the Earth.

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Starter

• What are five things you know about the Moon?

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The Moon’s Orbital Properties

• The Moon’s mean distance from Earth is 384,000 km.

Distance varies due to the Moon’s slightly elliptical orbit around Earth.

Astronomers have determined the Moon’s orbit to within a few centimeters.

They fire a laser at reflectors placed on the Moon by Apollo astronauts and measure its round trip.

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Physical Properties

• The Moon is ¼ the size of Earth.– Its radius is approximately 1738 kms.

• The Moon’s mass is about 1/80 of Earth’s (7.3 X 1022 kg.

• The Moon’s density is significantly less than Earth’s (3,300 kg/m3 versus 5500 kg/m3).– Suggests that the Moon contains fewer heavy

elements such as iron.

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Physical Properties

• Because the Moon is significantly less massive than Earth, its gravitational field is much weaker. – It is about 1/6 that of Earth’s – making the shots of

Apollo astronauts bounding across the Moon in large leaps.

– A person weighing 180 pounds on Earth weighs only 30 pounds on the Moon.

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Physical Properties

• There is no appreciable atmosphere– This is a result of the Moon’s weak gravitational

field.The Moon is not massive enough to retain an atmosphere.

The Moon’s “escape” velocity for a molecule is only 2.4 km/s compared with Earth’s 11.2 km/s.

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Physical Properties

• Any primary or secondary atmospheres the Moon may have once had, are gone forever.

• With no atmosphere, the Moon has no protection from interplanetary space. – This fact is crucial in understanding its surface

evolution and current appearance. – Without the moderating influence of the

atmosphere, temperatures on the surface vary widely (up to 400 K at the equator). It is equally cold at night or in the shade.

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Studying Earth Via the Moon

• How can scientists use the moon to study the Earth?

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Studying Earth Via the Moon

• Proposed moon based observatory focusing on Earth and the sun.– Education: would give us whole pictures of Earth

along with the stitched together composite photos we have now.• The photos would be internet accessible in real time,

with interpretation, to the public.

– The images would be hyperspectral giving us lots of different views of and information about the dynamics of Earth.

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Studying Earth Via the Moon

• One example of the hyperspectral analysis of Earth would be to help to study heliophysics and aeronomical data (i.e. allowing us to better understand the relationship between space phenomena, especially the sun’s, and our weather).

– A moon observatory would also allow us to more easily study Earth’s photometric signature of biological life. • By studying the biologically altered reflected light, we

might be able to use that information in our search for exoplanets with life.

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Studying Earth Via the Moon

• Photometric Earth data also is useful for studying Earth’s past and understanding how Earth’s climate and life has changed. Example: http://arxiv.org/abs/1110.1340

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Studying Earth Via the Moon

• There are no plate tectonics on the moon, so the moon’s surface is not being renewed like Earth’s. – Therefore, the moon has a very old surface.

• History of impacts – because of no plate tectonics, we get an idea of how frequently impacts would have been.– The “seas (mare)” are in fact large impact craters.

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Studying Earth Via the Moon

• Water on the moon and water on Earth are likely from the same source.– By studying volcanic glass samples from the moon,

scientists have been able to look at the ratios of deuterium to protium (the two stable hydrogen isotopes). Deuterium is “heavy hydrogen” and makes “heavy water.”

– Deuterium to protium ratios appear to be quite low, which is indicative of it having come mostly from carbonaceous meteorites – not comets.

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Studying Earth Via the MoonKnowing more about water on the moon should give us insight about how Earth came to be a “water world.”

A water hunting rover will be deployed to the moon in 2017.

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NASA Tour of the Moon

• https://www.youtube.com/watch?v=2iSZMv64wuU

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Quick Review

• Why does the Moon have no significant atmosphere?

• How is the distance to the Moon most accurately measured?

• Employ the concept of escape speed to explain why the Moon has no significant atmosphere?

• How can the moon be used to study the Earth?