STARSSTARS

What are stars?What are stars?

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Please pick up the TWO STARS packets from the back and sit down. Fill in the upper right and READ through the fill in the blank notes sheet to see what you know. We will begin our notes shortly

Stars are self-luminous spheres. Stars are self-luminous spheres. Self luminous means that stars Self luminous means that stars generate their own light.generate their own light. This makes stars different from This makes stars different from

planets, moons, asteroids, and planets, moons, asteroids, and comets, all of which shine by comets, all of which shine by REFLECTING light.REFLECTING light.

Stars are different in other Stars are different in other ways:ways:

They possess far more mass They possess far more mass (stuff).(stuff).

They have different They have different compositions.compositions.

They are hotter.They are hotter. Most are bigger that planetary Most are bigger that planetary

objectsobjects

Lets use the sun, our nearest star as an Lets use the sun, our nearest star as an example. It is a self luminous, gaseous example. It is a self luminous, gaseous sphere. It has no solid surface. Its size sphere. It has no solid surface. Its size is about 100 times the Earth and its is about 100 times the Earth and its mass is about 300,000 times that of mass is about 300,000 times that of the Earth. Its core temperature is 27 the Earth. Its core temperature is 27 million degrees Fahrenheit and its million degrees Fahrenheit and its visible surface is 10,000 degrees visible surface is 10,000 degrees Fahrenheit. The Sun is made up of Fahrenheit. The Sun is made up of mostly hydrogen and helium. The mostly hydrogen and helium. The heavier elements carbon, oxygen, heavier elements carbon, oxygen, nitrogen, iron, and gold make up only nitrogen, iron, and gold make up only about 2% of the Sun’s mass.about 2% of the Sun’s mass.

The Sun’s luminosity, its brightness –The Sun’s luminosity, its brightness –referred to as one solar luminosity. referred to as one solar luminosity. This is comparable to 4 trillion one-This is comparable to 4 trillion one-hundred-watt light bulbshundred-watt light bulbs

Our Sun is rather average. Some Our Sun is rather average. Some stars are bigger, more massive, stars are bigger, more massive, and brighter. Others are and brighter. Others are smaller, less massive, and less smaller, less massive, and less bright. Some stars are single bright. Some stars are single like the Sun. Others have one like the Sun. Others have one or several companion stars. or several companion stars. Some stars are much older than Some stars are much older than the Sun. Others have been the Sun. Others have been formed very recently.formed very recently.

Interesting FactInteresting Fact

The Earth intercepts about one-half The Earth intercepts about one-half billionth of the energy radiated by billionth of the energy radiated by the Sun. If we could harness all of the Sun. If we could harness all of the energy the sun radiates in one the energy the sun radiates in one second, we’d have enough energy second, we’d have enough energy to satisfy the current US energy to satisfy the current US energy consumption for about 4 million consumption for about 4 million years.years.

What makes a star shine?What makes a star shine?

Stars are nuclear furnaces. Stars Stars are nuclear furnaces. Stars generate their own energy by generate their own energy by nuclear reactions in their super nuclear reactions in their super hot cores. This newly released hot cores. This newly released energy flows from the stars’ hot energy flows from the stars’ hot interiors to the cooler surface interiors to the cooler surface layers, where the energy is layers, where the energy is radiated into space. We see that radiated into space. We see that radiation and say the stars shine.radiation and say the stars shine.

Back to the sun as our example. Back to the sun as our example. The temperature is so hot in the The temperature is so hot in the core of the Sun that hydrogen core of the Sun that hydrogen atoms fuse into helium atoms atoms fuse into helium atoms with the release of large amounts with the release of large amounts of energy. It is the same process of energy. It is the same process that powers a hydrogen bomb that powers a hydrogen bomb explosion, the difference is that explosion, the difference is that the sun is not explosive and goes the sun is not explosive and goes on at a steady pace for billions of on at a steady pace for billions of years.years.

Most stars you see in the Most stars you see in the night sky get their energy night sky get their energy in this way. Eventually the in this way. Eventually the hydrogen core will become hydrogen core will become a helium core. The helium a helium core. The helium core will then fuse into core will then fuse into carbon and oxygen, with carbon and oxygen, with still more energy being still more energy being released.released.

Do stars shine forever?Do stars shine forever?Stars do not shine forever. Stars do not shine forever. Stars are of finite size. That Stars are of finite size. That means that stars have only means that stars have only a certain amount of nuclear a certain amount of nuclear fuel. Eventually they will fuel. Eventually they will use up all their fuel and use up all their fuel and fade.fade.

How long stars shine How long stars shine depends on how much depends on how much mass the have. Mass mass the have. Mass determines the amount of determines the amount of fuel stars have at birth. fuel stars have at birth. Mass also determines how Mass also determines how bright stars are, or how bright stars are, or how rapidly they consume fuelrapidly they consume fuel

The greater a stars mass, the The greater a stars mass, the greater is the amount of its greater is the amount of its nuclear fuel. However, the more nuclear fuel. However, the more massive stars are fuel guzzlers. massive stars are fuel guzzlers. They shine much brighter than They shine much brighter than less massive stars and use up less massive stars and use up their fuel very fast. So the more their fuel very fast. So the more massive stars have shorter lives.massive stars have shorter lives.

Our sun will last about 10 billion Our sun will last about 10 billion years ( we are currently about 5 years ( we are currently about 5 billion years into that life).billion years into that life).

Why are stars important to us?Why are stars important to us?

1.1. The Sun (our nearest star) gives us The Sun (our nearest star) gives us light and warmth.light and warmth.

2.2. The Earth was formed as a by The Earth was formed as a by product of the formation of the Sunproduct of the formation of the Sun

Our planet and other planets in the Our planet and other planets in the solar system came into existences solar system came into existences as by-products of the formation of t as by-products of the formation of t he sun.he sun.

Without the Sun, there would be no Without the Sun, there would be no Earth, and no life, as we know it.Earth, and no life, as we know it.

3. Carbon, Nitrogen, Oxygen and other elements 3. Carbon, Nitrogen, Oxygen and other elements needed for life were produced by earlier generations needed for life were produced by earlier generations of stars.of stars.

Nearly all of the elements heavier than hydrogen and Nearly all of the elements heavier than hydrogen and helium in today’s universe were manufactured in helium in today’s universe were manufactured in earlier generations of stars. The most massive of earlier generations of stars. The most massive of those stars ended in a super-energetic explosions, those stars ended in a super-energetic explosions, called supernovae, ejecting their heavy elements into called supernovae, ejecting their heavy elements into spacespace

Some 4.6 billion years ago, our sun and the planets Some 4.6 billion years ago, our sun and the planets formed from clouds of gas and dust enriched by formed from clouds of gas and dust enriched by heavy elements from earlier generation of massive heavy elements from earlier generation of massive stars.stars.

Stars Lab HomeworkStars Lab Homework Plot the 16 stars on the H-R Plot the 16 stars on the H-R

DiagramDiagram Define the 12 vocabulary words Define the 12 vocabulary words

on the back of your NOTES on the back of your NOTES packet.packet.