1.2 : The Moon

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What is the Earth's only natural satellite and at what distance does it orbit?
The Moon, which orbits the Earth at a distance of 380,000km (about 60 Earth radii).
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Why does the Moon lack any significant atmosphere?
Because of its weak gravitational pull.
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What is the Moon's rotational period?
27.3 days.
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What is the Moon's orbital period?
27.3 days.
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What is meant by the Moon being in captured orbit?
Only one hemisphere (the near side) ever faces the Earth due to its rotational and orbital periods being equal.
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How was the Moon's far side first observed?
Using a dual lens camera on the Soviet probe Lunik 3.
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Who were the first humans to traverse the Moon's far side?
The Apollo 8 astronauts.
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What are the lunar seas?
Large, dark plains of iron-rich balsaltic rock formed by ancient volcanic eruptions.
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What are the lunar highlands?
Lighter, mountainous, highly-cratered regions composed of anorthosite, a course-grained igneous rock.
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What is believed to have created the Moon's craters?
Collisions with solid bodies like meteoroids (or asteroids for the larger craters).
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What are rilles?
Narrow channel-like depressions in the lunar seas, most of which are believed to have been caused by lava flows.
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What are wrinkle ridges?
Long ridges (up to 100s of km long) thought to have been caused by the buckling of the lunar surface as a result of compressive forces within the cooling, contracting lava.
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How does the far side of the Moon differ from the near side?
It almost completely lacks any seas and is almost entirely mountainous and heavily cratered.
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What were the objectives of NASA's Apollo space programme?
To send humans to the Moon; collect lunar soil and rock; deploy scientific experiments on the lunar surface; win the 'race' to the Moon against the Soviet Union.
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Which Apollo mission successfully sent humans to the Moon?
Apollo 11.
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What did the Apollo 11 astronauts do on the Moon?
They spent 2.5 hours of EVA exploring their immediate region in the Sea of Tranquility. They planted the US flag, took photographs, spoke with President Nixon via radio, deployed scientific instruments (in EASEPs) and collected soil and rock samples.
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How do ALSEPs differ from EASEPs?
They perform more long-term studies of the internal structure and local environment of the Moon, transmitting data back to Earth via a simple radio antenna.
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How are ALSEPs powered?
Using a Radioisotope Thermoelectric Generator (RTG) controlled by a Central Station.
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What do ALSEP instruments measure and analyse?
The Moon's internal structure; the composition and pressure of the lunar atmosphere; the intensity and direction of the solar wind; changes in lunar gravity; micrometeorites and secondary particles ejected by meteorite impacts; lunar dust.
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Describe the Condensation/Co-formation Hypothesis.
The Earth and Moon formed at the same time and place from material within the solar nebula.
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Describe the Capture Hypothesis.
The Moon was formed a great distance from the Earth and was subsequently captured by the Earth's gravitational pull in a chance 'close encounter.'
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Describe the Fission Hypothesis.
A rapidly-spinning Earth caused a large blob of material to spin off (possibly creating what is now the Pacific Ocean) and form the Moon.
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In what ways have the Condensation/Co-formation, Capture and Fission Hypotheses been proved to be scientifically inaccurate?
Magnetometers were unable to detect the presence of any significant lunar magnetic field and lunar rock analyses confirmed the Moon to have a vastly different average density to Earth, implying that they were not formed together.
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What is the most commonly accepted hypothesis for the Moon's formation?
The Giant Impact Hypothesis -- a relatively young Earth was struck by a Moon-sized object (Theia) that probably shared the same solar orbit. During the impact, Theia and a large portion of the Earth's outer layers melted and merged to form the Moon.
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What are some examples of scientific evidence for the Giant Impact Hypothesis?
The relative abundances of oxygen isotopes in moon rocks is equal to those on Earth, suggesting they formed the same distance from the Sun; the lack of water in lunar rock that could have been vapourised in a high-energy impact.
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Other cards in this set

Card 2

Front

Why does the Moon lack any significant atmosphere?

Back

Because of its weak gravitational pull.

Card 3

Front

What is the Moon's rotational period?

Back

Preview of the front of card 3

Card 4

Front

What is the Moon's orbital period?

Back

Preview of the front of card 4

Card 5

Front

What is meant by the Moon being in captured orbit?

Back

Preview of the front of card 5
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