Stars and Galaxies

Stars and Galaxies

Introduction
What do you always see when you look up at the sky at night? All that you see existed by natural processes. Do you ever wonder about the rising and setting of the Sun? What implications does this have on human life?
In this chapter, you will understand the life cycle of stars together with their source of energy.

7.1: Nature of Stars
Although all that you observe in the sky existed by natural processes, they have implications on human life. In this regard, one needs to understand the nature of these bodies.

Activity 7.1 Understanding the nature of stars Part (a)
Key question: Explain how the behaviour of stars behave.
What you need: Note book, pens, ICT resources and relevant text books Initial question: How are stars different from planets?

What to do: (in groups)

1. Use an ICT resource or any relevant text book and research about stars.
2. Share your findings with others through a discussion.
   ! Conclusion and Application
3. What do you understand by the term stars?
4. Explain where stars are found.
5. Discuss when stars become visible to humans.
6. Explain the importance of stars to humans.
   Part (b)
   What to do (In groups):
7. Study the picture in Figure 7.1 which represents a small section of a night sky taken by a telescope.

2, Share your findings with others for further discoveries.

3. Identify the colours exhibited by stars.
4. conclusion and Application)
5. Explain what you think enables stars to stay in groups.

7.2: Colour and Temperature
In day to day life, the word colour is casually used to define the physical appearance of objects. However, in the study of stars and galaxies, scientists use colour to make a number of meaningful conclusions as you will explore in activity 7.2.

Activity 7.2 Investigating more about stars
Key question: What does colour represent in the study of stars.
What you need: Candle, match box, note book, pen, ICT resource, relevant text books.
Initial question: Identify and explain whether all stars in the night sky look the same?
What to do (In groups):

1. Using a match stick, light up a candle as shown in Figure 7.2.

2. Study the candle flames and writedown the observations made in your note book.
3. Discuss your findings with other members.
   Conclusion and Application
4. Use colours to state which part of the flame is at a;
   (a) higher temperature
   (b) lower temperature

5. Suppose the candle represents a star, describe how you WOUld identify a hotter star from a number of other stars.
   The idea of studying colour in relation to temperature is of great importance during the study of stars. Find out more about colour and temperature of stars
   in activity 7.3
   Key question: Describes the different classes of stars.
   What you need: ICT resource, relevant text books, notebooks, and pens
   Initial question: What is the basis of classifying stars?
   What to do (In groups):
6. Conduct a research on how stars are classified in terms of colours.
7. Share your findings with others.
   Conclusion and Application
8. Identify the different spectral classes of stars.
9. Organise the classes in order of decreasing temperature.
10. In which class does our sun belong?
11. Discuss about the importance of the knowledge of star classification.

7.3: Energy in Stars
Think about the total amount of energy you obtain from the sun in just a single day. Imagine how this will be in a period of one year! In this section, you will understand how stars produce energy.
Activity 7.4 Understanding the source of energy in stars
Key question: Explain how stars produce energy.
What you need: ICT resource, relevant text books, notebooks, and pens
Initial question: What is an energy source?
What to do (In groups):

1. In your respective groups, use the internet or a library resource and research about how stars produce energy.
2. Share your findings with the whole class for further discovery.
   Conclusion and Application
3. Identify the most abundant chemical elements found in stars. Explain the process by which stars generate energy.

4. Discuss and state the energy changes which take place in a star.
5. Suppose you have a red and a blue star, identify and explain which of the two stars has a higher chemical composition than the other. Stars emit large amounts of energy which supports a number of earth based processes such as photosynthesis, generation of electric power,
   preservation of food and many others.

7.4: Evolution of Stars
You have always seen the sun rising from the east, providing us with various forms of energy and then setting in the west. But, have you ever thought about how long the sun has been providing us with light and energy? In other words, what do you think could be the sun’s age. Did you know that our sun will also die! In activity 7.5, you will understand how stars get born and live until they die.

Activity 7.5 Understanding the life cycle of stars
Key question: Explain how stars get born and spend their life time.
What you need: Note book, any resource, relevant text books and writing material.
Initial question: Suppose you have a blue and red star, which of the stars has more fuel?
What to do (In groups):

1. Study Figure 7.3 which describes the whole process of how stars evolve during their life time.

2. Research and make notes about each of the following stages of star evolution:
   (g) Neutron star
   (d) White dwarf
   (a) Protostor
   (e) Planetary nebulae
   (b) Red giants
   (f) Black hole
   (c) Supernova
3. Share your findings with other groups through a discussion.
   Conclusion and Application
4. Identify and write down the factor(s) that determine the path of evolution to be followed by a star.
5. At what stage of evolution is all the star’s fuel used up?
6. What happens to the temperature and stability of stars when all their energy is used (for both low and large massive stars).

Self Check
Suppose you have a blue star and a red star. Explain which of the two stars contains more fuel than the other. Hence state which star is older than the other.

7.5: The Sun
At an earlier stage, you learnt about photosynthesis where green plants manufacture their own food in the presence of sunlight. In addition, recall what brings about the changes in seasons from time to time as previously learnt in Senior Two. Carry out activity 7.6 to investigate more
about the sun.

Activity 7.6 | Investigating more about the sun
Key question: Explain how relevant the sun is to human life.
What you need: Note book, ICT resource, relevant text books, and writing
materials.
Initial question: How would the world be without the sun?
What to do (In groups);

1. Use the available resources and make research about the sun in the
   following areas:
   (a) Spectral class of the sun

(b) Composition of the sun
(c) Mass of the sun

2. Share your findings with other groups for further discoveries.
   Conclusion and Aoplication
3. what form of energy is obtained from the sun?
4. Suggest at least three (3) uses of the sun.
5. Give the location of the sun.
6. Identify the colour of the sun.
7. Describe the geometrical shape of the sun.
8. Identify whether the sun is a low massive or large massive star.
9. Explain the life cycle of the sun.
10. What is the sun’s current stage of evolution. Hence state the fate of the sun.

7.6: Galaxies
In section 7.1 , you learnt about the nature of stars. What did you find out about stars? In this section, you will learn about a collection of a large number of stars. In this regard, a collection of such stars is known as a galaxy. In this section you will explore what galaxies are and how such a large number of
stars can exist in a galaxy.

Activity 7.7 Investigating the different views about the nature of galaxies Key question: Explain the nature of galaxies.
What you need: Internet resource, relevant text books, note books, and writing material.
Initial question: What could be that faint irregular glowing strip of light visible across the dark night sky as shown in Figure 7.5?

What to do (In groups):
For thousands of years, people of various cultures had different views about
the glowing strip of light across the night sky. Most of these views were in form of stories or beliefs.

1. Using any available ICT resource or text books, research about the different understanding of the glowing strip in the night sky.
2. Share your findings with other members for further discovery.
   Conclusion and Application
3. Explain how each of the following cultures explained this irregular strip of visible light across the dark night sky:
   (a) Chinese (b) Egyptian (c) Polynesian (d) Greek
4. In your own opinion, develop a report explaining how traditions in Uganda might have explained this irregular strip of visible light across the dark night sky.

Activity 7.8 Understanding the nature of galaxies
Key question: Do you think all galaxies look the same?
What you need: ICT resource, relevant text books, notebooks, and writing material.
Initial question: Identify the force which keeps two or more bodies in space.
What to do (in groups):

1. Watch a you tube video about galaxies or use any available research
   material to find out more about galaxies.
2. Share your findings with other members through a discussion.
   Conclusion and Application
3. Identify and name the different types of galaxies.

4. Study the pictures in figure 7.6 which shows some of the different galaxies which exist in the universe. You are required to explain which of the three galaxies consists of young stars.
5. Identify and name our Galaxy and write down underwhich type does it belong.

Chapter 7 Summary
In this chapter you have leant that;
Stars exist in groups but not in isolation and differ in terms of colour.

Blue stars contain a higher amount of fuel as compared to red stars.

Red stars are older as compared to blue stars which are still burning fuel. e Our sun is an example of a star which will eventually turn out to be a white dwarf.

Galaxies are large collection of stars, gas and dust all gravitationally bound together.
Galaxies can be elliptical, Lenticulas, Spirals or irregular galaxies. We are in a spiral type of galaxy called the Milky way galaxy.