science form 3 chapter 9

8/3/2019 Science Form 3 Chapter 9

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CHAPTER 9 : STAR AND GALAXIES

9.1 The Sun

Characteristics of the Sun

1. At the centre of the Solar System, lies our veryown star known as the Sun.

2.The Sun is nearly 110 times bigger than theEarth.

3.The Sun appears bigger and brighter than all theother stars.This is because the Sun is the nearest

star to Earth.

4.The Sun is the largest object in the Solar System.The mass of the Sun is about 98% of the total

mass of the Solar System.

Structure of the Sun

Figure 9.1 Structure of the Sun showing some

phenomena on its surface

1.The core is the innermost layer of the Sun.Thetemperature of this layer can rise to

15000

000

C.

2.The surface of the Sun consists of three gaseouslayers: photosphere, chromosphere and corona.

The photosphere

1.The photosphere is the innermost atmosphericlayer of dense gases. It is considered as the

surface of the Sun.

2.The visible light that reaches Earth from the Sunoriginates from the photosphere

.

3.The photospheres experiences turbulence, muchlike the surface of a simmering pot of water.

This is due to the explosive eruptions of energy

on the surface of the sun.

4.

Sometimes, interactions with the Suns magneticfield result in the appearance of sunspots on the

photosphere.

The chromosphere

1.The chromosphere is the layer above the visiblephotosphere.

2. Solar energy passes through this region on itsway out from the centre of the Sun. The

temperature of this layer ranges between 6 000C

and 20000C.

3.The chromosphere glows red because hydrogengives off a reddish colour at these high

temperatures.

The corona

1.The corona is the extremely hot outermost layerabove the chromosphere.

2.Temperatures in the corona can reach over1000000C.

3. It is the thickest layer, stretching several millionkilometres into space.

Phenomena on the Suns surface

1.Prominences, solar flares and sunspots areexamples of phenomena that occur on the

surface of the sun.

2.These phenomena are believed to occur becauseof the changes in the magnetic field of the sun .

Prominences1.Prominences are immense clouds of glowing

gases that erupt from the upper chromosphere.

2.The loops or arches of gases may shoot as highas 100 000 kilometres from the surface of the

Sun. This allows some of the surface gases,

mainly hydrogen and helium, to escape into

space.

3.Prominences can last for two to three months andcan be seen during solar eclipses.


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Solar flares

1. Solar flares are the result of violent energyexplosions in complex sunspots groups.

2. Solar flares release gases and charged particlesfar into space.

3. Solar flares make the night sky above the polesappear colourful . this is known as an aurora.

Sunspots

1. Sunspots are dark regions which are visible onthe photosphere.

2. Sunspots appear dark because they are muchcooler than their brighter surroundings. The

temperature in these regions is about 4 000C.

Effects of the Suns phenomena on

Earth

1.The phenomena that occur on the surface of theSun have various effects on Earth.

2. a. The eruptions of prominences and solar flaresrelease large amounts of solar material into

space.

b. Gases that escape to space carry a stream of

electrically charged particles of energy.

c. The continuous flow of these particles from

the surface of the Sun causes a phenomenonknown as solar wind.

3.When the solar wind blows past Earth, there areeffects on the following.

4.Communications systemsa. Solar wind affects radio communication as it

causes radio signalsto fluctuate.

5.Navigation systemsand compassesa.Radio signals from transmitters are used by

ships and aeroplanes to determine their

locations.

b. Intense solar flares send out continuousstreams of electically charged particles which

interfere with the Earths magnetic field and

compasses.

6.Satellitesand astronautsa. The ultraviolet rays and X-rays given off by

solar flares heat up the Earths upper

atmosphere. As a result, satellites have to

orbit further up to prevent them from falling

back to Earth. Their lifespans are also

shortened.

7.Power generationa. The charged particles interfere with Earths

magnetic field and induce surges in the

electric current along power transmission

lines.

b.This overloads the power grids and causesblackouts over large areas.

8.Global climatea. Sunspots bring about changes in temperature,

humidity and atmospheric pressure, which

affect the weather conditions on Earth.

b.Wind, land and sea breezes are a result of theeffects of sunspots.

9. Formation ofaurorae1. Aurorae result from a collision between the

charged particles of the solar wind and the gas

molecules in the atmosphere of the Earth.This interaction causes them to emit a visible

light.

Generation of energy by the Sun

1.Solar energy is generated deep in the core of theSun through a process called nuclear fusion.

2.Nuclear fusion is a nuclear reaction in whichseveral atoms of one element combine to form a

different element.3. In the nuclear fusion process at the Suns core,

four hydrogen nuclei combine to form a helium

nucleus and a large amount of energy is

produced.

4.The energy generated is carried to the surface ofthe Sun and released as light and heat.

9.2 Stars and Galaxies in the

UniverseDefinition of a star

1. A star is a celestial body that releases its ownheat and light. It is a big ball of hot gases.

2. Stars are made up of dust and gases likehydrogen and helium. They generate energy

through nuclear reactions.


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The Sun as star

1.The Sun is a medium-sized star. It is the closeststar to Earth. Therefore, the Sun appears big,

bright and hot, when compared to the other stars

in the sky.

2. It is formed in a huge cloud of gas and dustcalled nebula.

3. It is a huge sphere made up mainly of hydrogenand helium. It generates heat and light and

releases energy through nuclear fusion.

Various types of stars

1. Astronomers use some of these characteristics toclassify the stars.

The colour and temperature of stars

1.The colour of a star indicates its temperature.2.The hottest stars are blue and the coldest stars

are red.

3.The Sun, which is yellow in colour, is a star ofaverage temperature.

4. Stars can be divided into seven classes based ontheir temperatures.These are O, B, A, F, G, K

and M.

Table 9.1 the colour and temperature of stars

Class Colour SurfaceTemperatureC

Example

O BlueMore than

25000Spica

BWhitish-

blue11000 25000 Rigel

A White 7 500 11000 Sirius

FYellowish

- white6 000 7 500 Procyon

G Yellow 5000 6 000 The Sun

K Orange 3 500 5000 ArcturusM Red Less than 3 500 Betelgeuse

Size

1. Stars are of different sizes. They can beclassified as neutrons, dwarfs, giants and

supergiants.

2.The smallest star is the neutron star which has adiameter of about 10 kilometres.

3.The Sun is a medium-sized star. Most stars areabout the same size as the Sun. A dwarf is a star

that is about the same size as the Sun. A white

dwarf is a star smaller than the Sun.

4. A giant star is a star about twenty times biggerthan the Sun.

5. A supergiant star is a star that is more than 100times the size of the Sun.

Brightness

1. Long ago, the brightness of a star was known asthe apparent magnitude.This was determined

by naked eye.2.The brightness of a star depends on factors such

as the surface temperature , size and distance

from Earth. Classifications using the naked eye

are not accurate.

Formation of stars

1. Stars are formed within huge clouds of gases anddust called nebulae.

2. A nebula consists mainly of gases such ashydrogen and helium and dust that collect as a

result of thepull of gravitybetween the particles.

3. A star is formed when a nebula is pulled inwardstowards the core until it becomes compact. As

the nebula collapses, it starts to spin.

4.The gravitational force increases and this causesthe material within the nebula to condense. As a

result, the temperature and pressure of the gases

and dust particles at the centre increase.

5. a.When the temperature reaches 15000 C ,nuclear fusion takes place at the core of the

nebula.

2.Hydrogen atoms fuse together to form heliumatoms, releasing a large amount of heat and

light energy.

6.The ball of gas starts to shine and a new star isborn.7.The star continues to generate heat and light

energy through the nuclear fusion reactions that

take place in its core.

8. Once a star is stable, its size remains constant.Deadth of stars

1.The lifespan of a star depends on its size.


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2. a. A star with a small mass has a longer lifespanwhen compared to a star with a big mass.

b.Small stars ( smaller than the Sun ) mayfinally die after more than 10 billion years but

super-large stars may not survive more than

100 million years.

3. Once the hydrogen fuel is used up and nuclearfusion is completed, the core of the star starts to

shrink.The star is said to be dying.4. a. The star cools, undergoes further changes

depending on the mass of the star and then

eventually dies.

b.A star will become either a white dwarf, aneutron star or a black hole when it dies.

Figure 9.2 Formation and death of Star

Galaxies

1. A galaxy is a group of millions or billions ofstars held together by gravity.

2.There are millions of galaxies scattered atrandom throughout the Universe. Each galaxy

has its own shape, size and luminosity, and

contains different bodies.

3.There are three basic types of galaxies.a. Elliptical galaxies

b.Spiral galaxiesc. Irregular galaxies.

The Milky Way

1. On a clear night, we can see a band of lightspreading across the sky.This is our own galaxy,

theMilky Way.

2. It is home to Earth and the Solar System.

3.The Milky Way is a Spiral Galaxy. It is shapedlike a flat disc and has projections.

4.The centre of the Milky Way has many old starswhile its spiral limbs have a lot of dust, gases

and young stars.

Figure 9.3The Milky Way

The Universe

1.The Universe consists of matter, energy andspace.

2.The Universe is everything you see around you.It is unimaginably huge.

3.The origin of the Universe is still unanswered but many astronomers support the Big Bang

theory.

4. Astronomers believe that the Universe is stillexpanding and galaxies are also breaking up.

5. Until today, astronomers still do not know theexact size of the universe.

Position of the Solar System in the

Universe

1.The Milky Way and millions of other galaxiesmake up the Universe.

2.Thus, the Solar System is only one tiny part ofthe whole Universe.


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9.3 The Universe as a gift

from God

The extent of the Universe

1.No one really knows the extent of the Universe.2.The Universe that is observed through the most

powerful telescope we have today may be only a

small portion of the real physical Universe.

3. If the current Big Bang theory is correct, theUniverse is 15 billion years old.We can assume

that the size of the Universe is about 15 biliion

light years.

The Universe is not permanent

1. All the stars in the galaxies in the Universegenerate light and heat energy through nuclear

fusion.2.The stars shine by burning hydrogen.When the

source of hydrogen in the Universe is exhausted,

all the stars will burn out and die.3.The gravity of the Universe may become so great

that it will bring all matter in the Universe back

together and the Universe will collapses into

black holes.4. It is, therefore, true to say that everything that

exists in the Universe is not permanent.The importance of the Sun to life on

Earth

1. Earth and other planets are linked to the Sun by agravitational force.The gravitational force of the

Sun is always present to keep Earth in the right

position to receive light and heat from the Sun.

2.Without light and heat from the Sun, life cannotexist on Earth.

3.The Sun provides light energy and heat energydirectly to living organisms.

4. All energy on Earth originates from the Sun.5.Heat energy from the Sun can lead to the

formation of clouds, rain, wind and droughts.

6. Green plants carry out the process ofphotosynthesis by absorbing and converting thesolar energy from the Sun into chemical energy.

This energy is stored in the food synthesised by

plants.

7.During photosynthesis, green plants also removecarbon dioxide from the air and increase the

supply of oxygen which is needed for life to

exist on Earth.

8. Solar cells convert solar energy into electricalenergy for our daily use.

The importance of the Moon to life

on Earth

1.The Moon influences life on Earth directly onindirectly.

2.The most obvious influence of the Moon onEarth is ocean tides.

3.When the Moon orbits close to Earth, the pull ofits gravity results in high tides. This, in turn,

causes erosion and the displacement of the

Earths surfaces which affect life on Earth.

science form 3 chapter 9

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