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Earth in the Solar System –

Essential Question: How does the position of Earth in the solar system affect conditions on our planet?

8.3 — The solar system is composed of planets and other objects that orbit the sun.

GRADE-LEVEL CONCEPT 8.3.a

Gravity is the force that governs the motions of objects in the solar system.

1. Earth is part of a system of celestial bodies that are grouped together around a central star, the Sun. This system includes objects of different masses and composition such as planets, moons, asteroids, minor planets, and comets. These objects move in predictable paths determined by gravity.
2. Gravity is a force of attraction between two objects. The strength of gravitational force depends on the total mass of the two objects and the distance between them. The greater the total mass, the greater the force of gravity. The greater the distance between two objects, the less the force of gravity.
3. The difference between an object’s mass and its weight is explained by gravity. Mass is the measure of the amount of matter in an object; weight is the force of gravity between an object and the celestial body it is on. Bodies in the solar system have different masses; therefore the same object has a different weight on each celestial body.
4. Objects in the solar system are held in their predictable paths by the inward-pulling gravitational attraction of the very massive sun. The interaction of the center-pulling force of gravity with a moving object’s inertia (tendency to keep moving) keeps one object in circle-like motion (revolution) around another. This causes planets to orbit around the center of the solar system and moons to orbit around planets.
5. The Earth and other planets move through space in two ways: rotation on an axis and revolution around the sun. Earth revolves around the sun in a near-circular path, explaining cyclical phenomena such as seasons and changes in visible star patterns (constellations).
6. The time it takes for an object to complete one revolution around the sun depends on the speed at which it is moving and the size of its orbit. Objects more distant from the sun’s gravitational pull move slower than those that are closer. Earth’s period of revolution is about 365 days (year); planets that are more distant from the sun take longer to orbit (revolve) around the sun, resulting in longer years.

C28. Explain the effect of gravity on the orbital movements of planets in the solar system.

GRADE-LEVEL CONCEPT 8.3.b

The motion of the Earth and moon relative to the sun causes daily, monthly and yearly cycles on the Earth.

1. Earth rotates around an axis or rotation, a line going through the center of the earth from the north pole to the south pole. The tilt of Earth’s axis relative to its orbital path, combined with the spherical shape of the earth, cause differences in the amount and intensity of the sun’s light striking different latitudes of the earth.
2. Earth experiences seasons as northern or southern hemispheres are tilted toward the sun over the course of its 365-day revolution period. Earth’s tilt causes seasonal differences in the height of the perceived path of the sun and the number of hours of sunlight. Seasons are not related to a change in distance between the Earth and the Sun, since that distance changes very little.
3. The moon changes its position relative to the earth and sun as it revolves around the earth in a period of about 29 days. The same half of the moon is always reflecting light from the Sun; some of the reflected light reaches Earth. Phases of the moon are explained by changes in the angle at which the sun’s light strikes the moon and is reflected to Earth. The relative position of the Sun, Earth and moon can be predicted given a diagram of a moon phase.
4. Eclipses occur when the moon, Earth and sun occasionally align in specific ways. A solar eclipse occurs when the when the moon is directly between the Earth and the sun (during new moon phase) and the moon blocks the sun’s light, creating a moving shadow on parts of the earth. A lunar eclipse occurs when the Earth is directly between the moon and the sun (full moon phase), the Earth blocks the sun’s light, casting a shadow over the moon.
5. Ocean tides on Earth are caused by the moon’s gravitational force pulling on large bodies of water as the Earth and moon move around each other daily. The regular daily and monthly movement of the water (tides) can be predicted.

C29. Explain how the relative motion and relative position of the sun, Earth and moon affect the seasons, phases of the moon and eclipses.

Grade Level Expectations

1. Relate the strength of gravitational force between two objects to their mass and the distance between the centers of the two objects and provide examples.
2. Describe in writing how gravitational attraction and the inertia of objects in the solar system keep them on a predictable elliptical pathway.
3. Distinguish between rotation of Earth on its axis and its elliptical revolution around the sun.
4. Investigate and report in writing how the Earth’s revolution around the sun affects changes in daylight and seasons.
5. Compare the revolution times of all the planets and relate it to their distance from the sun.
6. Conduct and report on an investigation that shows how the Earth’s tilt on its axis and position around the sun relates to the intensity of light striking the Earth’s surface.
7. Use a model to demonstrate the phases of the moon relative to the position of the sun, Earth and moon.
8. Develop a model or illustration to show the relative positions of the Earth, sun and moon during a lunar and solar eclipse and explain how those positions influence the view from Earth.

SCIENTIFIC LITERACY TERMINOLOGY: Force, gravity, orbit, revolution, year, period, mass, weight, rotation, hemisphere, season, phase, new moon, solar eclipse, lunar eclipse, tides.