3/3/2012

[Type the document subtitle] | Sarah Broussard and

Caitlin Owen

LHSD MOON?

Table of contents.

Page 1 How was the moon

formed?

Page 2 Composition

Page 3 Size- distance from earth?

Page 4 Phases of the

moon

Page 5 Orbit? Page 6

Effects on the earth

Page 7 Missions to the moon

Page 8 ADEVERTISMENT

How was the moon

formed?

Before astronauts went to the

Moon there were several main

theories about how the Moon formed. One of the goals of the

Apollo missions was to try and choose which theory fit best,

but in the end, a completely new theory was born. Before

we look at all the different theories, we need to look at

some of the differences and similarities between the Earth

and Moon:

The Earth has a large iron

core, but the Moon does not.

Earth has an average

density of 5.5 g/cm3 and the Moon has an average

density of 3.3 g/cm3 (because it is depleted in

iron). The Moon has exactly the

same oxygen isotope composition as the Earth,

whereas Mars rocks and

meteorites from other

parts of the Solar System (e.g. the asteroid belt)

have much different isotope compositions.

Co-accretion

This theory says that the Earth

and Moon formed (accreted) in

the same part of the Solar

System from similar building

blocks, and that the Moon is a

sister planet to the Earth. This

theory failed because it can’t

explain why the Moon is

depleted in iron compared to

the Earth.

Fission

Fission describes the somewhat

crazy idea that the young Earth

was spinning so fast that it

spun a lump of material off that

went on to form the Moon. This

theory fails because it defies

the laws of physics!

Giant Impact

You’ve already heard about the

Giant Impact theory, which is

the current favored formation

mechanism for the Moon. This

theory accounts for both the

similarities and the differences

between the Earth and Moon’s

composition. It assumes that

the Earth’s iron had already

drained into the core by the

time the impact happened, and

that the impactor also

contained an iron core. The

majority of debris thrown out

by the giant impact came from

their rocky mantles, and the

core of the impactor melted on

impact and merged with the

iron core of the Earth.

There is one thing this theory

doesn’t explain, however, and

that is why only one Moon

formed, or why we don’t see

evidence for this happening elsewhere in the Solar System!

Composition

What is the Moon made of? Start

by looking at its

surface. This

picture shows

it very well. There

are light areas

and dark areas. The dark areas

are called seas, but they do not

contain water. The seas are flat

regions, whereas the light areas

are rugged and are higher on

average. For this reason, they are

also called highlands.

Across the whole surface, craters

caused by meteoric impacts are

evident. The craters are much

more enhanced and frequent

within the light areas.

In the years from 1969 to 1972

the Moon has been explored by

man. Astronauts brought back to

Earth some samples of lunar

soil, so it has been possible to

analyze and date those rocks.

It has been found that the

younger lunar rocks are the dark

ones, those of the seas, and that

they are 3.2 billion years old. The

older ones are the light rocks of

the highlands, and they are 4.6

billion years old.

Even if the mass of the Moon is

just one hundredth of that of the

Earth, the ratio of the mass of the

Moon over that of the Earth is

very large, if one compares it to

the case of the other planets.

Leaving aside the Pluto-Charon

system, the Earth-Moon system

is indeed a unique case in the

Solar System. Generally

speaking, satellites are much

smaller than the planets which

hold them into an orbit. A well

known phenomenon is connected

to this peculiarity. The tides.

Size- distance from earth? 1 pixel = 600 kilometers The average distance between Earth and Moon is approximately 30 times Earth's

diameter. If you could fly to the Moon at a constant speed of 1000 kilometers per hour, which is the speed of a fast passenger jet, it would take sixteen days to get there. Apollo astronauts reached the Moon in less than four days even though they coasted "uphill" almost the entire distance. They got a fast start.The Sun happens to be 400 times the Moon's diameter, and 400 times as far away. That coincidence means the Sun and Moon appear to be the same size when viewed from Earth. A total solar eclipse, in which the Moon is between the Earth and Sun, blocks the bright light from the Sun's photosphere, allowing us to see the faint glow from the corona, the Sun's outer atmosphere. When the Moon is at apogee, it is 11% farther from Earth than it is at perigee. This is far enough that it cannot entirely block the bright light, so eclipses which occur near apogee are not total.

Perigee 363,300 km

Mean

384,400 km

Apogee

405,500 km

Gravitational interaction (tides on the Earth caused by the Moon) transfers kinetic energy from Earth to the Moon, slowing Earth's rotation and raising the Moon's orbit, currently at a rate of 3.8 centimeters per year.Earth and Moon Compared The Moon has approximately 1/4 Earth's diameter, 1/50 Earth's volume, and 1/80 Earth's mass. Earth is very dense overall (it is the densest planet in the Solar System), but the Moon is light for its size. The difference is partly because Earth has a large core of iron and other heavy metallic elements, while the Moon has only a small core, if it has a core at all. The Moon's surface gravity is 1/6 of Earth's, and escape velocity from the surface is about 1/5 of Earth's. The Moon's surface is covered with rock and grit that are mostly dark-gray minerals, so it reflects light poorly compared to Earth, which always has highly-reflective clouds. The Moon reflects visible light about 1/3 as well as Earth, and because of its

much smaller size, has a visual brightness less than 1/40 that of Earth, when both are fully illuminated and seen from the same distance -- a difference of four stellar magnitudes.

Earth Moon

Mean diameter 12,742 km 3,476 km

Volume 1.08321 x 1012

km3

2.199 x 1010

km3

Mass 5.9736 x 1024 kg 7.349 x 1022

kg

Mean density 5.515 3.342

Surface gravity 9.78 m/s2 1.62 m/s2

Escape velocity 11.2 km/s 2.38 km/s

Visual albedo 0.367 0.12

Visual

magnitude -3.86 +0.21

At right: Earth and Moon to the scale of 1 pixel = 50k The Moon's surface area is a bit greater than Africa's.

Phases of the moon

Orbit? The Moon's orbit is fiendishly difficult to explain, moving as it does around a rotating Earth, which together form a "double-planet" system that orbits around the Sun. It is a classic example of a three-dimensional, gravitational three-body problem. The Moon's peculiar bulge -- to which the French mathematician Pierre-Simon Laplace first drew attention in 1799 -- makes the problem even more complex.

Garrick-Bethell and colleagues now think that the strange bulge can be accounted for if the Moon moved along a very different orbit than it does now (see figure). Based on simple classical mechanics, rather than computer simulations, the MIT team suggest that when the Moon was just 100--200 million years old it was less than 30 Earth radii away, compared to about 60 Earth radii now.

As well as being much closer to Earth, they also believe the Moon had a much more elliptical orbit at that time. They calculate that its "eccentricity" -- a measure of how much an ellipse differs from a circle -- was 0.61, compared to

just 0.05 today. (A circle, in contrast, has an eccentricity of zero.)

Moreover, they believe that the Moon may have been spinning much faster than it is today and behaved a bit like Mercury does today -- rotating three times about its own axis for every two revolutions about the Sun (a so-called 3:2 resonance). Now, of course, the Moon spins just once for every revolution around the Earth, which is why we can never see its far side. The team also showed that the bulge can be explained by a 1:1 resonance with an eccentricity of 0.49 and semimajor axis of 22.9 Earth radii.

According to Garrick-Bethell's team, the proximity of the Moon to the Earth, together with its elliptical orbit, were ideal conditions for the bulge -- which was still forming as the Moon cooled -- to "freeze" into its present form. This explanation also ties in with the most widely accepted theory of the Moon's origins, which says it was created when a massive Mars-like object crashed into the Earth. In this theory, the Moon formed at about 4 Earth radii and it has been gradually moving away from us at a rate of about 3.8 cm a year ever since.

Effects on the earth

The gravitational attraction that the Moon

exerts on Earth is the cause of tides in the

sea. The tidal flow period is synchronized

to the Moon's orbit around Earth, but the

phase isn't. The tidal bulges on Earth,

caused by the Moon's gravity, are carried

ahead of the apparent position of the

Moon by the Earth's rotation, in part

because of the friction of the water as it

slides over the ocean bottom and into or

out of bays and estuaries. As a result,

some of the Earth's rotational momentum

is gradually being transferred to the

Moon's orbital momentum, resulting in the

Moon slowly receding from Earth at the

rate of approximately 38 mm per year. At

the same time the Earth's rotation is

gradually slowing, the Earth's day thus lengthens by about 15 µs every year.

The angular diameters of the Moon and

the Sun as seen from Earth overlap in

their variation, so that both total and

annular solar eclipses are possible. In a

total eclipse, the Moon completely covers

the disc of the Sun and the solar corona

becomes visible to the naked eye. Since

the distance between the Moon and the

Earth is very slightly increasing over time,

the angular diameter of the Moon is

decreasing. This means that several

million years ago the Moon always

completely covered the Sun on solar

eclipses so that no annular eclipses

occurred. Likewise, in several million

years the Moon will no longer cover the

Sun completely and no total eclipses will

occur. Eclipses happen only if Sun, Earth

and Moon are lined up. Solar eclipses can

only occur at new moon; lunar eclipses can only occur at full moon.

The Moon is most clear at night, but can

sometimes be seen during the day. The

Moon (and also the Sun) appear larger

when close to the horizon. This is a purely

psychological effect. The angular diameter

of the Moon from Earth is about one half

of one degree. During the brightest full

moons, the Moon can have an apparent

magnitude (the amount of light received

from the object) of about −12.6. For

comparison, the Sun has an apparent

magnitude of −26.8.For any location on

Earth, the highest altitude of the Moon on

a day varies between the same limits as

the Sun, and depends on season and

lunar phase. For example, in winter the

Moon comes highest when it is full, and

the full moon comes highest in winter.

Like the Sun, the Moon can also give rise

to an optical effect known as a halo (an

optical phenomenon that appears near or

around a light source).The event known

as a blue moon is related to the western

calendar system. A blue moon is the

second of two full moons to occur in the

same calendar month. Blue moons occur

infrequently (thus the saying once in a

blue moon to denote a rare event),

because the length of the calendar month

in this system is close to the length of the

period of the moon's phases. They are not

impossible, because every month except

February is longer than this period by 1 or

2 days. Blue moons occur every 2.72

years. The next blue moons will be on June 30, 2007; and December 31, 2009.*

Missions to the moon

The physical exploration of the

Moon began when Luna 2, a

space probe launched by the

Soviet Union, made an impact on

the surface of the Moon on

September 14, 1959. Prior to that

the only available means of

exploration had been observation

from Earth. The invention of the

optical telescope brought about

the first leap in the quality of

lunar observations. Galileo

Galilei is generally credited as

the first person to use a telescope

for astronomical purposes;

having made his own telescope

in 1609, the mountains and

craters on the lunar surface were

among his first observations

using it.

In 1969, NASA's Project Apollo

first successfully landed humans

on the Moon. They placed

scientific instruments there and

returned rocks to Earth.

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