Science F3 Chapter 9-Stars and Galaxies-Part 1-PPT

Choong XH, Catholic High School (2010)

STARS AND GALAXIESScience Form 3 Chapter 9

Last update: 26/8/2010


Part A The Sun

F3 C9 STARS AND GALAXIES9.1 The Sun


Characteristics of the Sun

• The Sun is a star. It is the nearest star to the Earth

• The Sun is in the centre of the Solar System ( 太阳系 )

• It is the biggest object in the Solar System


Characteristics of the Sun

• It has a large force of gravity because of its big mass.

• The force of gravity causes the planets ( 行星 ) and asteroids ( 小行星 )in the Solar System to orbit around it



Part B The Structure of the Sun




Structure of the Sun

• The Sun has an atmosphere ( 大气层 ) which can be divided into three layers:– The corona ( 日冕 )– The chromosphere ( 太阳

色球层 )– The photosphere ( 光球

层 )



The Corona

• The corona is the outermost layer of the Sun’s atmosphere. It is actually a layer of gas boiled off from the sun

• The corona extends for thousands of kilometers into outer space


The Corona

• It is the hottest layer of gas in the Sun’s atmosphere, with a temperature of about 1 500 000oC

• The corona is a faint whitish blue region and can only be seen during an eclipse of the Sun

• The corona gives out X-rays.


The Chromosphere

• The chromosphere is a layer of gas below the corona

• “Chromosphere” means a sphere of colour, so called because of its reddish-pink colour.

• This layer of gas is about 5 000 km thick


The Chromosphere

• Its temperature can rise as high as 50 000oC

• It can only be seen during an eclipse of the Sun because it is not bright


The Photosphere

• The photosphere is a layer of heavy gas which can be seen from the Earth as a bright lighted surface

• “photosphere” means a sphere of light

• The photosphere has a temperature of about 6000oC


The Photosphere

• Its surface appears very rough because the gases from the core bubble through it.

• Solar flares, prominences and sunspots erupt from its surface


The Core

• The core is made up of hydrogen and helium under high pressure.

• The core is the hottest part of the Sun with a temperature of about 15000 000oC

• Thermonuclear reactions which are continuously going on in the core generate the Sun’s heat and light


Part CPhenomena on the Sun’s Surface



• Phenomena occurring on the Sun’s surface are:– Sunspot– Flares– prominences




Sunspots


Sunspots

• Sunspots are dark areas on the surface of the Sun

• These areas are dark because they are cooler than the other parts o the Sun’s surface

• Sunspots will disappear after several hours or several weeks

• They are caused by magnetic fields which slow down the emission of heat from the core of the Sun


Sunspots


Sunspots

• They are of different sizes and some may have diameters of several thousand kilometres

• They usually occur in pairs• They appear to move

across the Sun’s surface because the Sun is rotating from west to east.


Sunspots



Flares 太阳耀斑


Flares

• Solar flares are bursts of light from the Sun’s surface

• They give out a lot of energy although they last from several minutes to several hours only.

• They can reach a temperature of 5 000 000oC


Flares

• They also release charged particles into outer space, and some of these particles reach the Earth




Prominences 日珥



Prominences

• Prominences are clouds of burning hydrogen and helium exploding from the Sun’s surface

• These clouds of hot gases appear bright red and curved, and may reach a height of more than 100 000 kilometres

• They can have a temperature of 10 000oC


Prominences

• The hot gases cool down after some time and are pulled back to the Sun by the Sun’s gravity. At the same time some of the gases escape into outer space

• The gases which escape into outer space form the solar wind ( 太阳风 )


Prominences

• The solar wind causes the tail of a comet to point away from the Sun


Prominences


Part DEffects of Sunpots, Flares and Prominences on

the Earth





Effects of Sunspots, Flares and Prominences on the Earth

• Sunspots, flares and prominences on the Sun’s surface radiate X-rays, ultraviolet rays, the solar wind and charged electric particles into outer space.

• Some of the these rays and charged particles reach the Earth and have effects on the Earth



• These rays and charged particles influence the weather and climate on the Earth. It is believed that a large number of sunspots on the Sun’s surface can cause disturbing weather conditions on the Earth



• The electrically charged particles will collide with the particles in the Earth’s atmosphere and cause radio and television interference



• The electrically charged particles are deflected by the Earth’s magnetic field towards the north and the south poles. These produces green, yellow and red coloured lights in the sky near the poles at night. These coloured lights are called the aurorae 北极光


Aurorea


Aurorea


Aurorea


Aurorea


Aurorea


Aurorea


Part EGeneration of Energy by the Sun



Generation of Energy by the Sun

• The sun is the source of energy of the entire Solar System

• Energy is generated by thermonuclear reactions in the core of the Sun where the temperature and the pressure are extremely high



• During thermonuclear reactions in the core of the Sun, light hydrogen atoms combine to form heavier helium atoms with the release of large quantities of heat energy and light energy.

• The temperature reached in this reaction is about 15,000,000oC



• The energy generated in the reaction is brought from the core to the surface of the Sun by radiation and convection

• Most of the energy radiated from the Sun is in the form of heat and light. Only a fraction of the heat and light reaches the Earth



• When all the hydrogen in the Sun is used up, the Sun will become a small quiet object in outer space.


Questions – TEST YOUR UNDERSTANDING



Questions

1. Name the 3 layer of the Sun’s atmosphere2. Which layer of the Sun’s atmosphere can only

be seen in a total eclipse of the Sun? Why?3. Why do sunspots appear to move across the

Sun’s surface from the west to the east?4. What causes aurorae in the Earth’s north and

south poles?5. How is heat generated in the Sun’s core

Documents

Science F3 Chapter 9-Stars and Galaxies-Part 1-PPT