Mass: 1.99 x 1030 kg. Diameter: about km = 100 x the Earth diameter. Density: about kg/m3

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2 Mass: 1.99 x 1030 kg Diameter: about km = 100 x the Earth diameter Produces a strong gravitational forces: about 28 times greater than the gravitational force produces by the Earth Temperature: Surface-6000C Centre of the Sun C Density: about 1500 kg/m3

3 Surface of the Sun About 500km thick Consists of dense gases The temperature is about 6000C Outermost layer Extends hundreds of km from the centre of the Sun The temperature can reach C Middle layer Can only be seen during an eclipse The temperature about C

4 Sunspots ü Dark areas on the Suns ü Cooler than the surrounding areas ü May last for more than a week Prominences Throw out matter from the Sun into space at speeds from 600km/s to more than 1000km/s Last for a few days or even for a few month

5 Solar Flares ü violent and spectaculars gas explosion that often occurs near sunspots ü made up of numerous charged gaseous particles from the Sun shooting outward at high speed into outer space ü interact with Earth s magnetic field producing dazzling light display called aurora Aurora Borealis, (northern light) Aurora Australis, (southern light)

6 q Composition of Sun is helium and hydrogen q Because of the temperature, thermonuclear reactions occur in the Sun s core q Release large amount of heat and light energy q Temperature reach C q Energy from the core is distributed by the processes of radiation and convection q Sun energy is emitted as electromagnetic waves

7 Star with mass <1.4 x Sun s mass Star with mass 1.4 to 3.0 x Sun s mass Star with mass >3 x Sun s mass

8 The diagram above shows the formation and death of stars Stars begin as a large cloud of gas and dust called nebula After ten thousands of year collapse, a hot core will be formed When the supply of gas in a star runs out, the star dies When a star with a mass of up to 1.4 times the Sun s mass, it will become a red giant The red giants then contracts, releasing its gas and turns into white dwarf When a star with mass of between 1.4 and 3.0 times the Sun s mass, it will become red giant then continues swell even more to become supergiant The supergiant then explodes producing supernova As the supernova collapse, a neutron star is formed When a star with mass of more than 3.0 times the Sun s mass, it swell up become red giant then become supergiant The supergiant then explodes producing supernova As the supernova collapse, its core becomes so massive that its gravity sucks everything including light into it The core is called a black hole

9 Stars are grouped together in vast collections called galaxies Our Solar System with only one star, the Sun, forms a tiny part of galaxy called the Milky Way Galaxy are classified into various type based on the shaped. Three common types of galaxies are spiral, elliptical and irregular shaped

10 Large galaxy with 20k to 100k light years of diameter Disc-shaped centre : older spiral arms : new stars, Gases and dust 30% of galaxies are spiral Diameter of galaxy is 3k to 10k light years Smooth & rounded / oval in shape Brightest at the centre & fades towards the edge Consists of mainly old star 60% of galaxies are elliptical Diameter of this galaxy is 25k to 32k light years No definite shape & exists in various forms Consists of bluishwhite stars (young star) & nebulae 10% of galaxies are irregular

11 A spiral-shaped galaxy with a diameter of 100k light years & is about 10k light years thick Consists of old stars at the centre at the center & nebulae (dust and gases) at spiral arms Stars in Milky Way galaxy are so close together & observed as hazy patches The Sun is 30k light years from the center of Milky Way The Sun takes 200 million years to orbit the centre of the Milky Way

12 Sunlight is essential for photosynthesis Encourage the development of technologies based on the Moon travelling Main Source of Energy Affect the occurance of ocean tidal Causes water to evaporate produces rain Calendars based on phases of the Moon

13 Nobody knows exactly how the Universe began or how it will end. Among the various scientific theories about the formation of the Universe, the most widely accepted scientific theory is the Big Bang theory According to the Big Bang theory, about 12 billion to 15 billion years ago, our Universe began with enormous explosion. Since then, the Universe has forever been expanding everywhere at the same time