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Characteristics of Stars and The Life of Stars Chapter 21 2012.

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Presentation on theme: "Characteristics of Stars and The Life of Stars Chapter 21 2012."— Presentation transcript:

1 Characteristics of Stars and The Life of Stars Chapter 21 2012

2 How are stars formed and what are they made of? There are huge clouds of Hydrogen gas in outer space. (Nebula) Over time gravity causes gas to come together. Once enough gas comes together, there is enough pressure to cause a nuclear reaction “lighting” the star. (a star is born) Nuclear fusion is what causes a star to “burn” Hydrogen is converted into helium during nuclear fusion.


4 1.Imaginary patterns made up of stars are called constellations. 2.What gases are stars made of? Hydrogen and Helium 3.How do stars produce energy? Nuclear fusion

5 Classifying Stars 1. What are some characteristics scientists use to classify stars? By their color, temperature, size, composition, and brightness 2. What can a star’s color tell us? It can tell us the stars temperature. Cooler stars appear red and hotter stars are blue 3. The largest stars are called red giants or super giants. 4. The smallest stars are called neutron stars.

6 5. What is a spectrograph? A spectrograph breaks light into colors and produces an image of the resulting spectrum. Dark lines in the image can ID the chemicals present. How is it used? A spectrograph can tell scientists what distant objects are composed of.

7 The spectrum and spectrographs

8 Brightness of stars 6. What does the brightness of a star depend on? Size and temperature 7. What is apparent brightness? A stars brightness as seen from Earth. Affected by distance 8. What is absolute brightness? The brightness a star would have if it were a standard distance from the Earth. 9. Why is finding a stars brightness so difficult? An astronomer must find the apparent brightness and the distance from the Earth.

9 10. What is a light year? The distance that light can travel in one year. (9.5 million million kilometers) Milkyway galaxy 100,000 light years across. The Andromeda galaxy is 2.5 million light years away from Earth

10 11. What the heck is a parallax? The apparent change in position of an object when you look at it from different places

11 Hertzsprung- Russell Diagram 12. What is the Hertzsprung- Russell diagram? The diagram plots the temperature and absolute brightness the star would have.



14 Size comparison of stars




18 Life of Stars Nebula- a large cloud of gas and dust spread out in an immense volume. A star on the other hand is made of a large amount of gas in a small volume. How does a star form from a cloud of gas? Gravity pulls gas and dust into a dense ball eventually triggering nuclear fusion. The life of a star depends on its mass. -Stars with less mass than the sun burn their fuel slowly and can live up to 200 billion years. Medium sized stars can live up to 10 billion years.

19 The Death of Stars What happens to a star the begins to run out of fuel? The core shrinks, and the outer portion expands. What happens when it completely runs out of fuel? The star becomes a white dwarf, a neutron star or a black hole. White Dwarfs Planetary Nebula- The outer parts of a dying star drifting into outer space forming a glowing cloud of gas White dwarf- the core of a dying star the size of Earth with as much mass as the sun. (1 spoonful has as much mass as a large truck. Supernova When a high mass star begins to die it turns into a supergiant. When a supergiant runs out of fuel it can suddenly explode. This explosion is called a super nova.

20 White dwarf compared to Earth

21 Neutron Star Describe a neutron star: neutron stars are the remains of high mass stars. Smaller and denser than white dwarfs. They can contain as much as three times the mass of the sun but only 25 km in diameter! -A spinning neutron star is called a pulsar.

22 Black Holes What is a black hole? A black hole is an object with gravity so strong nothing, not even light can escape it. How can astronomers detect black holes if they cannot see them? They use indirect evidence like gas near a black hole that spins faster and faster. They can also detect heat and X- rays coming from it.

23 Life and Death of a Star

24 Wow! A single sugar cube sized amount of white dwarf would weigh about 1 ton. A white dwarf was once the size of the sun, but has been squeezed down to the size of the Earth. A white dwarf has burned off all its fuel and only carbon remains.

25 Wow continued Neutron stars A neutron star is about 20 km in diameter and has the mass of about 1.4 times that of our Sun.mass This means that a neutron star is so dense that on Earth, one teaspoonful would weigh a billion tons!dense

26 How does gravity in space keep objects in orbit?

27 We are made of stars! Once helium runs out, the nuclei of carbon, oxygen, and other elements begin to fuse. Since the heaviest element created in a star by nuclear fusion reactions is iron, a large iron core eventually forms at the center of everything. At this point, gravity becomes overwhelming, the core collapses, and an explosion occurs (supernova), during which outer layers of gas and heavy elements are ejected to space.

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