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Earth in Space Benchmark Study Guide
1. Why do we experience day and night?
Half of Earth is always illuminated by the Sun, while the other half of Earth is in its own shadow, and is
dark. As an area on Earth rotates into the Sun’s light, that area experiences daylight. As an area on Earth
rotates away from the Sun’s light, that area experiences night.
2. Define the terms “rotation” and “revolution” as they relate to space science.
Rotation defines a planet’s or moon’s spin on its axis. Revolution defines a planet’s or moon’s orbit
around another solar system body.
3. Describe the Moon’s period of rotation and revolution.
The Moon’s period of rotation on its axis is 27.3 days, or about one month. The Moon’s revolution
around Earth also takes 27.3 days. Because the Moon’s rotation and revolution periods are equal, only
one side of the Moon ever faces Earth, the “near side”.
4. Describe the Earth’s period of rotation and revolution.
The Earth rotates on its axis every 24 hours, or 1 day. The Earth revolves around the Sun every 365 ¼
days, or 1 year. Since a calendar year is 365 days long, we add an extra day every 4 years to account for
the extra ¼ day.
5. Why can the Moon appear as large as the Sun even though we know the Moon is much smaller
than the Sun?
The Sun is 400 times farther away from the Earth than the Moon, and the Sun is also 400 times larger in
diameter than the Moon. This causes the two bodies to appear to be the same size.
6. Describe the relative sizes of the Sun, Earth and Moon.
The Sun is equal to 109 Earth diameters across. The Earth is 4 times larger than the Moon and about 30
Earth diameters away.
7. Why does the Sun appear to move across the sky each day?
The Earth rotates on its axis every 24 hours, or 1 day. As it does, the Sun appears to move across the
sky. Actually, it is Earth rotation that makes the Sun appear to move across the sky.
8. Why do shadow lengths change during the day? You may draw a picture to show changes in
shadow length relative to the Sun’s position in the sky.
As Earth rotates on its axis, the Sun appears to move across the sky. Shadow lengths depend on the
position of the Sun in the sky. When the Sun’s position in the sky is high (solar noon), shadows are short.
When the Sun’s position is lower (early morning/late afternoon), shadows are longer.
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9. Explain why shadow lengths change throughout the year.
Shadow lengths change throughout the year as Earth orbits the Sun and Earth’s position on its tilted
axis changes. When an area on Earth is tilted toward the Sun (summer), the Sun is high in the sky and
solar noon shadows are the shortest. When an area on Earth is tilted away from the Sun (winter), the
position of the Sun is lower and shadows are longer.
10. What causes seasons?
Seasons occur because of the tilt of Earth’s axis relative to the Sun. As Earth orbits the Sun, different
parts of Earth get more or less direct sunlight. (Summer-more, Winter-less)
11. How many degrees is Earth’s axis tilted?
23 ½ degrees
12. What causes the Moon to be illuminated? Looking at the Moon from space, how much of the
Moon always receives light from the Sun? Explain your answer.
The Moon gets its light from the Sun. Looking at the Moon from space, half of the Moon is always
illuminated by the Sun, unless there is a lunar eclipse. The illuminated part of the Moon that we can see
from Earth changes throughout the Moon’s orbit, causing lunar phases.
13. Sketch and label the phases of the Moon as they relate to the Sun and Earth.
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14. Draw a diagram of each eclipse listed below. Label the Moon, Sun, and Earth, umbra and
penumbra, and indicate that it is a total solar or lunar eclipse.
Solar eclipse:
Lunar eclipse:
15. Why do solar and lunar eclipses occur?
When the Moon aligns between the Sun and Earth and its shadow falls on Earth, the Sun’s light is
eclipsed causing a solar eclipse. If the Moon passes behind the Earth into its shadow, the Moon’s light is
eclipsed causing a solar eclipse.
16. During which phase of the Moon does a solar eclipse occur? Lunar eclipse?
A solar eclipse occurs during a New Moon. A lunar eclipse occurs during a Full Moon.
17. Why don’t we have eclipses every month?
The Moon’s orbit is tilted. This means that when the Moon passes between the Sun and Earth, the
Moon is normally lower than the Earth’s alignment with the Sun. When the Moon passes behind the
Earth, it is normally higher than the Earth’s alignment with the Sun.
18. Label the planets in their correct order in space.
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Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune
19. List the planets in order of size from smallest to largest.
Mercury, Mars, Venus, Earth, Neptune, Uranus, Saturn, Jupiter
20. Our 8 planet solar system is part of what galaxy and how are the planets categorized?
Our 8 planet solar system is part of the Milky Way galaxy. The planets within our solar system are
divided into two categories. The four inner planets, Mercury, Venus, Earth and Mars are called the
rocky planets. The four outer planets, Jupiter, Saturn, Uranus and Neptune are the called the gas
planets, or the gas giants.
21. What keeps the planets in orbit around the Sun?
The forces that keep planets in orbit around the sun are known as gravity and inertia. The inertia of the
planets and the pull of the sun combine to create a gravitational pull that keeps the planets in their
orbits. Sir Isaac Newton was the one to discover all this.
22. Where does gravity exist?
An object with mass attracts any other object with mass. The strength of that attraction depends on the
mass of each object and their distance from each other so gravity exists everywhere in the universe. So,
the farther an object is from the planets center, the weaker the pull between the planet and the object.
The closer the distance two objects are, the greater their gravitational force.