Unit 11, Chapter 31

Integrated Science

Unit Eleven: Astronomy

31.1 Earth and Moon

31.2 Solar System

31.3 The Sun

Chapter 31 The Solar System

Chapter 31 Learning Goals Describe how Earth’s dimensions were determined. Use the equation of universal gravitation to determine mass and

gravitational force. Explain why the moon stays in orbit around Earth. Describe the moon’s formation. Define the solar system in terms of gravity. Characterize the planets in terms of size, distance from the sun,

atmosphere, and period of orbit. Name and describe other objects found in the solar system. Describe the size and composition of the sun. Explain the process through which the sun produces energy. Identify and define the parts of the sun. Explain how the sun’s energy can be harnessed. Describe how a photovoltaic cell works.

Chapter 31 Vocabulary Terms asteroid astronomical unit comet gravitational force law of universal

gravitation gas planets meteor orbit

orbital speed satellite solar constant solar energy solar system

sunspots

terrestrial planets

tides

31.1 Earth and MoonEarth's Dimensions

— Earth’s shape is almost spherical except for a slight bulge at the equator.

— If you were to travel exactly once around along the equator, you would travel 40,076 km

— This distance is the circumference of Earth.

31.1 Earth and MoonEarth's Dimensions

— The diameter is 12,756 km and its radius at the equator is equal to half of this value, or 6,378 km.

— Because of its slight bulge at the equator, if you were to measure the radius from one of the poles it would be slightly less (6,357 km).

31.1 Earth and Moon Earth’s only moon

revolves around us at a distance of 384,400 kilometers (240,250 miles).

It is the only object beyond Earth that humans have visited.

31.1 Earth and MoonGravitational force is a

measure of the attractive force exerted by an object (planet or moon) on a 1 kg object held at its surface.

This quantity is measured in newtons or pounds.

31.1 Earth and Moon Orbital speed is the speed

required to achieve a balance between the pull of gravity on a satellite and its forward motion.

The orbital speed of the moon is about 3,700 kilometers per hour.

If the moon were any slower, it would fall toward Earth and eventually crash into it.

31.1 Earth and MoonKey Question:

What does the length of the year have to do with Earth's distance from the sun?

*Read text section 31.1 BEFORE

Investigation 31.1

31.2 The Solar System Through their observations of the night sky, ancient

observers noticed that five bright objects seemed to wander among the stars each night.

They called these five objects planets, from the Greek word meaning “wandering star."

31.2 The Solar System German mathematician Johannes Kepler (1571-1630)

discovered that the orbits of some of the planets were not perfectly round but slightly oval or elliptical in shape.

31.2 The Solar SystemThe solar system consists of the sun, the nine

planets and their moons, and a large number of smaller objects (asteroids, comets, and meteors).

The solar system is the region in space where the sun’s gravitational force is dominant.

The reason they don’t fall into the sun is because as they fall toward it, they are moving forward because of their inertia.

Astronomers often use the distance of Earth from the sun as a measurement of distance in the solar system. One astronomical unit (AU) is equal to 150 million km.

31.2 The Solar SystemKey Question:

How big is the solar system?

*Read text section 31.2 BEFORE Investigation 31.2

31.3 The SunThe sun’s diameter is 1.4 million km.About one million Earth could fit inside of the sun.The core of the sun is about 15 million °C.The coolest parts of the sun are nearly 4,000 °C.The outermost layer of the sun can stretch millions

of km into space.The sun is 150 million km from Earth.The sun spins around once every 27.4 days.The sun is about 5 billion years old.

31.3 The SunThe sun’s energy

comes from nuclear fusion.

Nuclear fusion occurs when the nuclei of atoms are joined, or fused.

31.3 The Sun In 1905 Albert Einstein proposed that matter can

be converted into energy.

His famous equation shows how huge amounts of energy can be created from a smaller mass.

E mc2=

31.3 The Sun

31.3 The SunThe sun has three regions:

— The chromosphere is a very hot layer of plasma, a high energy state of matter.

— The corona is the outermost layer of the sun’s atmosphere extending millions of kilometers beyond the sun.

— The apparent surface that we can see from a distance is called the photosphere, which means “sphere of light.”

31.3 The Anatomy of the SunSunspots are areas of gas that are cooler than the

gases around them.

31.3 Solar CellsPhotovoltaic (or PV) cells,

also called solar cells, are devices that convert sunlight directly into electricity.

You may have seen PV cells on calculators, watches, or some outdoor light fixtures.

They are made out of at least two layers of a semiconductor material such as silicon.

31.3 Solar Cells One layer has a negative charge,

and the other has a positive charge.

When light falls on the cell, some of it is absorbed by the semiconductor atoms, freeing electrons from the PV cells’ negative layer.

These electrons then flow through an external circuit and back into the positive layer.

The flow of electrons produces electric current.

31.3 The SunKey Question: How can we use energy from the sun to

generate electricity?

*Read text section 31.3 BEFORE Investigation 31.3