Chapter 9=Stars and Galaxies
9.1 The Sun
-The sun is the main source of energy for the Earth.-The sun is a giant ball of hot glowing gases and it spins around in space.
Characteristics of the Sun
-Size
-Colour
-Temperature
-Brightness
Structure of the Sun
=Just like the earth,the sun has an atmosphere is divided into three layer is known as corona,the niddle layer is called chromospheres,and the innermost layer is known as photosphere.
The corona is made up of a thin layer of gas.It is only visible during a total solar eclipse.It appears as abluish white layer.Its temperature 2000000 C.The chromospheres is about 9600 km thick,temperature 15000 C and during a solar eclipse chromosphere layer appears reddish.The photosphere is the surface of the sun as ssen from the earth.The center of the Sun is known as the core.Its temperature 15000000 C.This is because in the core,hydrogen is beign changed onto helium.This process releases energy.It is this energy that keeps the Sun shinning.
Phenomena on the Sun’s surface and their effects
=On the Sun’s bright yellowish surface, the photosphere layer, three major phenomena take place.
Sunspots appears as dark patches.They appear dark because they are cooler than other part of the surface.The sunspots do not last more than a few weeks.However,every 11 years, the sun is very active with many sunspots.Sunspots are caused by magnetic disturbances deep inside the sun.These disturbances can cause changes in the Earth’s climate.
Prominences or ‘giant flames’ are also seen in the photosphere.These can extand to many thousands of kilometers from the surface.Some surface gases,mainly hydrogen and helium,escape to outer space.Gases that escape carry a stream of energetic,electrically charged particles.These particles cause wind as solar wind.The wind is strongest during periods when many sunspots are visible and solar activity is high.Solar wind can effect satellite,radio,television,telegraph and telephone communications.The charged particles also cause an aurora.An aurora is a phenomena in which the sky in the polar regions appears colourful
In addition to sunspots and prominences,flares are seen on the photosphere.A flare is a huge cloud of hydrogen that causes violent explosions.The flares may reach the earth’s surface and cause disturbances to telecommunication.Solar Flares have been seen as static on some radios.
Sunspots appears as dark patches.They appear dark because they are cooler than other part of the surface.The sunspots do not last more than a few weeks.However,every 11 years, the sun is very active with many sunspots.Sunspots are caused by magnetic disturbances deep inside the sun.These disturbances can cause changes in the Earth’s climate.
Prominences or ‘giant flames’ are also seen in the photosphere.These can extand to many thousands of kilometers from the surface.Some surface gases,mainly hydrogen and helium,escape to outer space.Gases that escape carry a stream of energetic,electrically charged particles.These particles cause wind as solar wind.The wind is strongest during periods when many sunspots are visible and solar activity is high.Solar wind can effect satellite,radio,television,telegraph and telephone communications.The charged particles also cause an aurora.An aurora is a phenomena in which the sky in the polar regions appears colourful
In addition to sunspots and prominences,flares are seen on the photosphere.A flare is a huge cloud of hydrogen that causes violent explosions.The flares may reach the earth’s surface and cause disturbances to telecommunication.Solar Flares have been seen as static on some radios.
Generation of solar energy
=The sun’s energy comes from deep within its core.Here a process called nuclear fusion takes place.Briefly,hydrogen is changed into helium,forming huge amounts of energy where it is released as heat and light.
Definition of a star
=Stars are made up of dust and gases like hydrogen and helium.They generate heat and light through nuclear fusion,in the same way hydrogen bombs release their energy.
The Sun as a star
=The Sun is a star because it is huge sphere made up mainly of hydrogen and helium.Its energy is formed through nuclear fusion and it generate heat and light.It appears big and hot to us because it is the closer star to earthVarious types of stars
=Various stars can be compared and contrasted by looking at the similarities and differences in their size,brightness,colour and temperature.
Size
=The smallest star is about km in diameter.It is known as a neutron star.The white drawf star is also small but is bigger than the neutron star.Sun is a medium-sized star.The biggest star is known as a supergiant star.
Brightness
=The brightness of a star depends on its surface temperature,size and distance from the Earth.Ex:-of bright stars are Sirius and Rigel.
Colour and Temperature
=The colour of a star depend on its temperature.blue coloured star have the highest temperature,while red coloured stars have the lowest temperature.
Formation of Stars
=Stars are formed nebulae.A nebulae is made up of a cloud of dust,and gases like hydrogen and helium.The gravitational attraction between particles of the gases and dust pull them together.The strong attractive force also causes the temperature of the star to rise,thus causing the star to expand.If there is a balance between the force pulling the star together and the heat pushing the star outwards,the star will become stable star.The Sun is an example of a stable star.
Death of Stars
=When nuclear fusion of hydrogen and helium has been completed,the core of the star will get smaller and smaller.The star is said to be dying.A lot of heat is generate.As a result,hydrogen within this layer starts to burn .This causes the star to expand.During this stage,the star appears red in colour and it called a red giant.
If the red giant is not massive,a white dwarf will be formed.However,if the red giant is big enough,it will contract so quickly that a big explosion called a supernova will occur.A supernova is extremely bright.It can be seen in daylight.As a result of the explosion,a neutron star will be formed if the original star is a large star.If the original star is a super-large star,a black hole will be formed.It is called a black hole because light in it cannot escape.Any matter that enters it cannot escape too.
If the red giant is not massive,a white dwarf will be formed.However,if the red giant is big enough,it will contract so quickly that a big explosion called a supernova will occur.A supernova is extremely bright.It can be seen in daylight.As a result of the explosion,a neutron star will be formed if the original star is a large star.If the original star is a super-large star,a black hole will be formed.It is called a black hole because light in it cannot escape.Any matter that enters it cannot escape too.
Galaxies
=Our solar system is in the galaxy called the Milky Way.Galaxies can be classified according to their shape.There are three types of galaxies:-
a)Spiral
b)Elliptical
c)Irregular
The Milky Way
=The Milky Way is a spiral-shaped galaxy that is about 100000 light years from one side to the other.The star are not spread evenly in it.Here,the star are so close to another that they are observed as hazy patches.The solar system occupies a very small part of the Milky Way.It is situated about midway out to the edge in one of the spiral arms.
The Universe
=The Universe consists of all the matter,energy and space that exist.It contains billions of galaxies,star,planet,particles.
Chapter 10=Space exploration
Developments in Astronomy
=Astronomy is one of the oldest in sience.It involves the study of object in the Universe like planets,star and galaxies.
The Greeks were the first people to study astronomy.For example,they classified stars based on constellations.
Astronomers need instrument to help them observe object that are far away.In 1608, Hand Lippershey,a Dutch optician,invented the telescope.This started a new era in astronomy.Galileo Galilei,an Italian astronomer was the first man to observe object in space using a telescope.
Development in space exploration
=Major development in space exploration began after 1957.Since then,other development have helped scientists discover more about space.For example,space telescope have been put into orbit by rocket.These telescope have helped astronomer discover distant object in space that could not be seen before.Space probes,a type of spacecraft,send valuable images and data back to earth.
In 1961,Yuri Gagarin,a Russian astronaut become the first humen to orbit the earth in a spacecraft.1969,the American astronaut Neil Armstrong became the first humen to set foot on the moon.
In 1971,the first space station was launced by the Russians.Space stations are designed to stay in space for along period of time.Since 1981,space shuttles have been used to carry astronaut.These astronaut have helped retrieve and repair damaged satellities,as well as carry out research in space.
Satellites are used in areas such as communication,weather,monitoring, defence,navigation and environmental monitoring.
a)Communication satellites allow us to have instant radio and telephone communication.
b)Weather satellites monitar the world’s weather,enabling forecasters to predict weather hazards like typhoons and flood more accurately.
c)Navigation satellites guide ships and aircraft.
d)Military satellites help nations improve their security and defence.
e)Global Positioning System(GPS), is very important for search and rescue.
f)Environmental satellites survey the world’s resources.
Remote sensing means studying conditions on earth from space.Data is captured by remote sensing satellites and image are presented on a computer screen.There are two types of remote:-
a)Active remote sensing
=sends signals to earth
b)Passive remote sensing
=record the sun radiation
The Malaysian Centre for Remote Sensing(MACRES)is the body responsible for remote sensing projects in Malaysia.MACRES compiles research data on remote sensing and other related technologies such as GPS.
Space research and technology have helped in the manufacture of certain pure and high quality materials.Some example are microchips,crystals and special metals.
Space exploration helps us to learn about our Universe.There are many benefits derived from space exploration that can help improve the quality of life on earth.
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