Unit 4 - Exploring Our UniverseChapter 9 - The Solar System

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9.1 - Earth, Moon, and Sun Relationships

Day and Night: Earth’s Rotation

Our planet, the Earth, orbits the Sun - the largest and hottest object inour solar system. While Earth orbits the sun, it also spins on its own axis.This is called a rotation. A rotation takes almost 24 hours. This rotationcreates day and night.

Viewed from above the North Pole, Earth spins counter-clockwise. Thisexplains why the Sun appears to rise in the east and set in the west.

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Seasons: Earth’s Tilt and Revolution

Seasons occur all over the world but differ from region to region. InCanada, we have four seasons: spring, summer, autumn, and winter. NewZealand has the same four seasons, but they occur at opposite times.Why?

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The changing seasons are the result of Earth’s movement around the Sunand Earth’s tilted axis (titled at 23.5◦).

Earth travels around the Sun in an elliptical path called an orbit. Arevolution is one complete orbit of Earth around the Sun, a journey thattakes one year.

Because of this orbit and tilt, we have the seasons. For example, when thenorthern hemisphere is titled toward the Sun, we have summer.

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Earth’s Moon

A satellite is any object that orbits a planet. A moon is a natural satellite.Earth has only one Moon. It is much smaller than Earth and has noatmosphere.

The Moon is bright because it reflects the Sun’s light. However, the shapeof its bright part changes daily. Why?

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The Moon and Its Phases

The Moon’s phases are caused by the revolution of the Moon around Earthand our changing views of it. The phases are classified in eight categories:

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Eclipses

As Earth revolves around the Sun, and the Moon revolves around Earth,they sometimes line up in such a way that a partial or total shadow of oneobject is cast on another. Such overshadowing events are called eclipses.

Watch: “Lunar Eclipse” Watch: “Solar Eclipse”Unit 4 - Exploring Our Universe 7 / 13

Solar Eclipse

A solar eclipse occurs when the Moon lies directly between Earth and theSun, blocking all or part of the Sun’s light to viewers on Earth.

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Lunar Eclipse

A lunar eclipse occurs when Earth blocks out the Sun’s light shining onthe Moon, making the Moon briefly disappear. This happens when Earthlies directly between the Moon and the Sun.

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The Sun

The Sun is a star. A star is a body of electrically charged gas, or plasma,that emits energy from nuclear reactions taking place in its core.

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The Sun has a powerful magnetic field that causes four important eventsto take place on its surface and elsewhere:

1 Sunspots - is a region on the Sun’s surface that is cooler than thesurrounding areas. This indicates regions where the magnetic field isvery strong, slowing down convection.

2 Solar Prominences - a large, low energy, curved, bright stream ofparticles. This curve often forms a loop. It is shaped by the Sun’smagnetic field lines.

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3 Solar Flares - a high energy massive explosion at the surface of theSun. This sudden release of magnetic energy often flings hot plasmaout into space.

4 Solar Wind - The tremendous amount of energy at the Sun’s surfaceproduces a constant flow of particles streaming out of its surface outin all directions. Earth’s protective magnetic field, called themagnetosphere, deflects most of this solar wind.

Solar Flare Solar Wind crosses space and strikes Earth.

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An interesting product of solar wind:

Aurora Borealis - An aurora is a natural light displace in the sky. Aurorasform as particles from the solar wind are trapped by Earth’s magnetic fieldand are swept toward the North and South Poles.

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