Unit 1 - Science Literacy & Space
1.2 - Space
Day 4 - Due 10/1(A) & 10/2(B)
Introduction
On July 20, 1969, hundreds of millions of people all over the world witnessed something incredible. Never before had a human being walked on a planetary body other than Earth. But on that day, Neil Armstrong and Buzz Aldrin walked on the Moon (Figure below). More than 30 years later, the Moon remains the only place that humans have visited outside of our home planet.
Human explorations of the Moon, along with visits by rovers and satellites, have helped scientists learn a great deal about the geology of Earth’s only natural satellite. Much of what we know about the Moon was learned by astronauts visiting the Moon and from data collected by the Apollo missions.
On July 20, 1969, hundreds of millions of people all over the world witnessed something incredible. Never before had a human being walked on a planetary body other than Earth. But on that day, Neil Armstrong and Buzz Aldrin walked on the Moon (Figure below). More than 30 years later, the Moon remains the only place that humans have visited outside of our home planet.
Human explorations of the Moon, along with visits by rovers and satellites, have helped scientists learn a great deal about the geology of Earth’s only natural satellite. Much of what we know about the Moon was learned by astronauts visiting the Moon and from data collected by the Apollo missions.
Lunar Characteristics
The Moon is Earth’s only natural satellite, a body that moves around a larger body in space. The Moon orbits Earth for the same reason Earth orbits the Sun -- gravity. The Moon is 3,476 km in diameter, about one-fourth the size of Earth. The satellite is also not as dense as the Earth; gravity on the Moon is only one-sixth as strong as it is on Earth. An astronaut can jump six times as high on the Moon as on Earth! (By the way, lunar means having to do with the Moon.)
The Moon makes one complete orbit around the Earth every 27.3 days, relative to the fixed stars. This is the Moon's orbital period. The Moon also rotates on its axis once every 27.3 days. Do you know what this means? The same side of the Moon always faces Earth and so that side of the Moon is what we always see in the night sky (Figure below). The Moon makes no light of its own, but instead only reflects light from the Sun.
The Moon is Earth’s only natural satellite, a body that moves around a larger body in space. The Moon orbits Earth for the same reason Earth orbits the Sun -- gravity. The Moon is 3,476 km in diameter, about one-fourth the size of Earth. The satellite is also not as dense as the Earth; gravity on the Moon is only one-sixth as strong as it is on Earth. An astronaut can jump six times as high on the Moon as on Earth! (By the way, lunar means having to do with the Moon.)
The Moon makes one complete orbit around the Earth every 27.3 days, relative to the fixed stars. This is the Moon's orbital period. The Moon also rotates on its axis once every 27.3 days. Do you know what this means? The same side of the Moon always faces Earth and so that side of the Moon is what we always see in the night sky (Figure below). The Moon makes no light of its own, but instead only reflects light from the Sun.
The Lunar Surface
The Moon has no atmosphere. Since an atmosphere moderates temperature, the Moon’s average surface temperature during the day is approximately 225°F but drops to minus 243°F at night. The coldest temperatures, around minus 397°F, occur in craters in the permanently shaded south polar basin. These are among the coldest temperatures recorded in the entire solar system.
Earth’s landscape is extremely varied with mountains, valleys, plains and hills. This landscape is always changing as plate tectonics builds new features and weathering and erosion destroys them.
The landscape of the Moon is very different. With no plate tectonics, features are not built. With no atmosphere, features are not destroyed. Still, the Moon has a unique surface. One major lunar surface feature is the bowl-shaped craters that are caused by meteorite impacts (Figure below). If Earth did not have plate tectonics or erosion, its surface would also be covered with meteorite craters.
The Moon has no atmosphere. Since an atmosphere moderates temperature, the Moon’s average surface temperature during the day is approximately 225°F but drops to minus 243°F at night. The coldest temperatures, around minus 397°F, occur in craters in the permanently shaded south polar basin. These are among the coldest temperatures recorded in the entire solar system.
Earth’s landscape is extremely varied with mountains, valleys, plains and hills. This landscape is always changing as plate tectonics builds new features and weathering and erosion destroys them.
The landscape of the Moon is very different. With no plate tectonics, features are not built. With no atmosphere, features are not destroyed. Still, the Moon has a unique surface. One major lunar surface feature is the bowl-shaped craters that are caused by meteorite impacts (Figure below). If Earth did not have plate tectonics or erosion, its surface would also be covered with meteorite craters.
The motions of bodies in the solar system are, for the most part, regular and understandable. From Earth, the Sun rises in the eastern sky in the morning and sets in the western sky in the evening. If the Moon is full on Day 1, it will be full again on Day 28, and new on Day 14. The motions of Earth relative to the Sun, and the motions of the Moon and Sun relative to Earth affect different phenomena on Earth, including day and night, the seasons, tides, and phases of the Moon.
The Phases of the Moon
Like everything in the solar system except the Sun, the Moon does not produce any light of its own — it only reflects sunlight. As the Moon moves around Earth, different portions of the satellite are illuminated. This causes the phases of the Moon, so that our view of the Moon goes from fully lit to completely dark and back again.
It takes about 29.5 days for the Moon to make one cycle relative to the Sun and go through all the phases (Figure below). The time between two new Moon phases or two full Moon phases is 29.5 days. Remember that the Moon's orbital period is 27.3 days. The difference of 29.5 and 27.3 is that while the Moon is orbiting the Earth, the Earth is moving along in its orbit so it takes longer for the Moon to reach the same position relative to the Sun.
The Phases of the Moon
Like everything in the solar system except the Sun, the Moon does not produce any light of its own — it only reflects sunlight. As the Moon moves around Earth, different portions of the satellite are illuminated. This causes the phases of the Moon, so that our view of the Moon goes from fully lit to completely dark and back again.
- The Moon is full when Earth is between the Moon and the Sun and the Moon’s nearside is entirely lit.
- The Moon is at first quarter phase about one week later, when the Moon appears as a half-circle. Only half of the Moon’s lit surface is visible from Earth.
- The Moon is in a new moon phase when the Moon moves between Earth and the Sun and the side of the Moon facing Earth is completely dark. Earth observers may be able to just barely see the outline of the new moon because some sunlight reflects off the Earth and hits the moon.
- Before and after the quarter-moon phases are the gibbous and crescent phases. During the gibbous moon phase, the moon is more than half lit but not full. During the crescent moon phase, the moon is less than half lit and is seen as only a sliver or crescent shape.
It takes about 29.5 days for the Moon to make one cycle relative to the Sun and go through all the phases (Figure below). The time between two new Moon phases or two full Moon phases is 29.5 days. Remember that the Moon's orbital period is 27.3 days. The difference of 29.5 and 27.3 is that while the Moon is orbiting the Earth, the Earth is moving along in its orbit so it takes longer for the Moon to reach the same position relative to the Sun.
Solar Eclipses
A solar eclipse occurs when the new moon passes directly between the Earth and the Sun (Figure below). This casts a shadow on the Earth and blocks Earth’s view of the Sun
A solar eclipse occurs when the new moon passes directly between the Earth and the Sun (Figure below). This casts a shadow on the Earth and blocks Earth’s view of the Sun
A total solar eclipse occurs when the Moon’s shadow completely blocks the Sun (Figure below). When only a portion of the Sun is out of view, it is called a partial solar eclipse.
Solar eclipses are rare and usually only last a few minutes because the Moon casts only a small shadow (Figure below).
As the Sun is covered by the moon’s shadow, it will actually get cooler outside. Birds may begin to sing, and stars will become visible in the sky. During a solar eclipse, the corona and solar prominences can be seen.
A Lunar Eclipse
A lunar eclipse occurs when the full moon moves through Earth’s shadow, which only happens when Earth is between the Moon and the Sun and all three are lined up in the same plane, called the ecliptic (Figure below). In an eclipse, Earth’s shadow has two distinct parts: the umbra and the penumbra. The umbra is the inner, cone-shaped part of the shadow, in which all of the light has been blocked. The penumbra is the outer part of Earth’s shadow where only part of the light is blocked. In the penumbra, the light is dimmed but not totally absent.
A Lunar Eclipse
A lunar eclipse occurs when the full moon moves through Earth’s shadow, which only happens when Earth is between the Moon and the Sun and all three are lined up in the same plane, called the ecliptic (Figure below). In an eclipse, Earth’s shadow has two distinct parts: the umbra and the penumbra. The umbra is the inner, cone-shaped part of the shadow, in which all of the light has been blocked. The penumbra is the outer part of Earth’s shadow where only part of the light is blocked. In the penumbra, the light is dimmed but not totally absent.
A total lunar eclipse occurs when the Moon travels completely in Earth’s umbra. During a partial lunar eclipse, only a portion of the Moon enters Earth’s umbra. Earth’s shadow is large enough that a lunar eclipse lasts for hours and can be seen by any part of Earth with a view of the Moon at the time of the eclipse (Figure below).
Questions
1. Why is there no weather on the Moon?
2. How much do landscape features on the Moon change over time compared to landscape features on Earth? Explain your answer.
3. Why is the force of gravity on your body weaker on the Moon than on the Earth?
4. Explain how the positions of the Earth, Moon, and Sun vary during a solar eclipse and a lunar eclipse.
5. Draw a picture that shows how the Earth, Moon, and Sun are lined up during the new moon phase.
1. Why is there no weather on the Moon?
2. How much do landscape features on the Moon change over time compared to landscape features on Earth? Explain your answer.
3. Why is the force of gravity on your body weaker on the Moon than on the Earth?
4. Explain how the positions of the Earth, Moon, and Sun vary during a solar eclipse and a lunar eclipse.
5. Draw a picture that shows how the Earth, Moon, and Sun are lined up during the new moon phase.