Bellringer What phase of the moon must be occurring for you to be able to witness a total solar eclipse?

Earth’s Moon Notes

Earth/Luna Comparison Earth’s Diameter = 12,742 km Luna’s Diameter = 3,476 km (less than the United States is from California to NY) This means that if Earth were the size of a basketball, Luna would be the size of a tennis ball. Earth’s Circumference = 40,030 km Luna’s Distance from Earth = 384,000 km This means that if you were to take a string and wrap it around a globe 9.6 times, that string’s length would represent the distance from Earth to Luna.

Drawn to scale diagram of size and distance

Lunar Characteristics The moon is dry and airless. Compared to Earth, the moon is small and has large variations in its surface temperature. Using two lenses and a wooden tube, in 1609, Galileo Galilei invented the first telescope. Using it, he discovered that the moon was not the perfect sphere that the Greeks originally imagined, but was instead a large rock with an irregular surface and contained a variety of remarkable features.

The Lunar Surface Galileo noticed that on the surface of the moon, there were large, dark, flat areas which he named maria (Latin for “seas”). Galileo incorrectly thought that these were large oceans. We now know that these areas are hardened rock formed from huge lava flows that occurred between 3 and 4 billion years ago while Luna was still cooling off.

The Lunar Surface Also on the surface can be found massive impact craters. Some of these are hundreds of kilometers across. Scientists originally thought that these craters were formed from volcanic activity, but has since been determined to be created by meteoroid (chunks of rock and dust from space) impacts. Because the maria contain very few craters, it can be determined that most of the crater impacts formed before the maria, while the solar system was still full of leftover rock material from the forming planets.

Lunar Characteristics Despite the fact that the moon is about 1/4 the diameter of Earth, it is actually about 1/8 of Earth’s mass. Making it much less dense. It is believed that Luna’s overall density is very similar to Earth’s outer layers.

Lunar Characteristics Luna has no atmosphere, therefore she has no air. This is a result of Luna’s very low gravity, as well as the gravity of Earth pulling gasses towards it during its early development. Because of this, astronauts must wear specialized suits to explore the lunar surface.

Lunar Characteristics On the moon’s surface, temperatures range from 130°C in the direct sunlight to -180°C when it is facing away from the sun. This is also directly related to the fact that Luna has no atmosphere. Gases in an atmosphere help to keep heat in and block some other heat from entering (like the glass in a car). Without these gases, the moon gets all solar energy when facing the sun, and immediately releases the energy when it rotates away. Remember that Luna faces Sol for nearly two weeks at a time, then faces away for another two weeks.

Lunar Characteristics The moon has no liquid water. There is evidence that there is ice water near the lunar poles, as well as in deep craters where parts are always shaded from the sun. If a colony on the moon were built in the future, any such water would be very valuable. It would be very expensive to transport large amounts of water to Luna from Earth.

Lunar Origins When the solar system was still young (about 4.5 billion years ago), there was a large amount of rocks and smaller planet- like objects (planetesimals) flying around space. All evidence collected from the moon suggests that early in Earth’s development, a Mars-sized planetesimal named Theia collided with Earth. The result of this collision was a swath of mantle material being ejected into space and eventually coalescing into our moon.

Lunar Origins This collision of planetesimals (us and Theia) to form a natural satellite is known as the collision-ring theory.

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