The Sun - It is located at the centre of our solar system with all planets and objects (comets and asteroids) revolving around it Page 1 of 6 - It s gravitational pull keeps the planets and other objects in orbit around it and it takes 25 1 3 days to rotate in its own axis - 1 400 000 km in diameter ( 109 diameter of the Earth ) and 1.989 10 30 kg in mass ( 330 000 mass of the Earth) - The Sun has been in existence for about 4.5 thousand million years and is 1. 41 g cm 3 in density compared to water ( 1 4 density of the Earth) - The surface temperature of the Sun is 6000 o c and the temperature or the Sun s core is 15 10 6 o c The Sun s Atmosphere Corona - Outermost layer of gas and forms a circle of bluish-white light around the Sun - Only visible during the eclipse of the Sun and is about 1 500 000 o c Chromosphere - Bright-red layer of gas below the corona and only visible during eclipse of the Sun - Range of temperature ( 10 000 and 500 000 ) o c Photosphere - Compact layer of gas seen to be shining with yellow light from the Earth - Photosphere s surface appears turbulent because gases from the Sun s core are released to the surface and is responsible for radiating heat and light ( 6000 o c ) Sun s Core - Consists of hydrogen (74 %) and helium (25%) with a temperature of 15 000 000 o c - A nuclear reaction happens in the core all the time to generate and release heat and light energy - This reaction fuses hydrogen atoms to form helium atoms (Nuclear Fusion) - This reaction is the same as that which occurs in a nuclear reactor that produces energy Additional Information - A comet consists of ice and dust with its tail extending to several hundred million kilometers - An asteroid is a block of rock that orbits the Sun between the planters Mars and Jupiter - The average distance of the Sun from the Earth is 150 000 000 km and its light takes 8.3 minutes to reach the Earth
Labelled X Effects upon weather Page 2 of 6 Phenomena that Occurs at the Sun s Atmosphere Prominences - An explosion of hot gas that shoots out from the surface of the Sun with shiny bright light - Can be seen near the edge of the Sun during the eclipse (of the Sun) - The hot gas shoots out as far as 300-400 thousand kilometers and escapes into outer space but pulled back to the chromosphere subsequently by the gravitational force of the Sun - It emits charged particles and uv rays into outer space and can take place for a short while or last for several weeks - It can cause a flow of wind (solar wind) which consists of charged particles Solar Flares - Strong explosion of gases that happens suddenly on the surface of the Sun near sunspot groups - Happens when activities of the sunspots reach a peak every 11 years - Emits charged particles and rays like gamma rays and X-rays - Happens only for a few minutes or a few hours but releases a great deal of energy Sunspots - Dark spots on the surface of the Sun s atmosphere and usually exist in groups with different sizes - Has a lower temperature (4000 o c) then its surroundings (6000 o c) with a strong magnetic field - Occurs for a period of few hours to several months and their number reaches a peak every 11 years Effects of the phenomena on the surface of the Sun on Earth Effects upon Communications - Charged particles (solar flares) reach the North Pole or South Pole of the Earth & collide with gas molecules - Colourful lights (green, yellow, red) will be produced and can only be seen at night called aurora - The heat energy from the Sun affects temperature, atmospheric pressure, humidity, cloud formation, weather, climate, wind and ice on Earth - Believed that that quantity of heat increases when the phenomena occur - Charged particles and radiation from the sun (cosmic rays, X-rays, gamma rays) will collide with the particles with the Earth s atmosphere - It causes disturbance to the communications system (television and radio broadcasts, telegraph transmissions, telephone calls)
Stars and Galaxies in the Universe Page 3 of 6 - A star is a natural object in outer space that an release heat and light energy through nuclear reaction with its distance from Earth is measured in light years - Therefore, the Sun is a star that is nearest to the Earth and the bright stars in the sky can be seen by the naked eye at night Bright Star Colour The Universe as a Gift from God Sirius Rigel Deneb Vega Spica Arcturus Pollux Antares Capella Castor Reddish Reddish Reddish Whitish Whitish - All gases move by expanding outwards in the universe which means it is still expanding and becoming larger - All objects contained in the universe will not last forever like all the stars that may die one day because of the depletion of hydrogen gas for nuclear reactions - Galaxies will also disappear when all the stars in it die or burn out and when a Sun dies, the solar system will be destroyed - The Moon is also important as it enables certain animals to come out at night to carry out activities like hunting (owl) Supplies light energy to green plants to make food Supplies light energy that enables humans and animals to see Importance of the Sun Facilitate evaporation and condensation processes leading to occurence of rain Supplies heat energy to warm the Earth to provide a suitable temperature sustaining life
Page 4 of 6 - Colour depends on its temperature - Star with low temperature :Red - Star with high temperature : Blue Classification of Stars Colour and Temperature Size Colour of Stars Surface Temperature ( o c) Very blue 40 000 Blusih 18 000 Whitish Blue 10 000 White 7 000 Yellow 6 000 Orange 4 000 Red 3 000 Star Dwarf Star (white dwarf) Brief Explanation Very small star, even smaller than Earth Giant Star Big star that is 10 bigger than the Sun Different Stars have different sizes Supergiant Star Very big star that is 100 bigger than the Sun Brightness Star Apparent Magnitude Sirius - 1.46 Rigel + 0.12 Arcturus - 0.04 Capella + 0.08 - Apparent Magnitude : Measurement of Deneb + 1.25 brightness of objects from the Earth The Sun - 26.8 - The lower it is, the brighter the object The Moon (Not Star) - 12.6 Additional Information 1. Hipparchus introduced the classification system using apparent magnitude (120 BC) 2. Alpha Proxima is the second nearest star to the Earth (4.2 light years away) 3. Sirius (8.6 light years away) and Rigel (900 light years away)
Life Cycle of a Star Birth Page 5 of 6 A star is born from a nebula (large cloud of dust and gas) 1. Gases and particles in the nebula are pulled by a strong gravitational force to form a lump 2. Strong gravitational force causes the lump to shrink and compressed until it becomes very compact to form a core 3. The increasing gravitational force causes the core to become smaller and more compact 4. When the temperature and the pressure in the core becomes very high, nuclear reaction occurs 5. Hydrogen gas is turned into helium, releasing large amounts of heat and light energy 6. The core shines and a star is born Death A star will die when all the hydrogen gas in the core is used up (nuclear fusion) Moderate Size like the Sun (or 1.5 smaller) 1. Hydrogen atoms in the star are used up and nuclear reaction stops 2. The star expands because of decreasing gravitational force and forms a red giant 3. Outer parts of the star drift out into outer space leaving the core (white dwarf) 4. The white dwarf (star that is dense and compact) becomes increasingly cold 5. The white dwarf continues to become colder and eventually leaves a black body (black dwarf) and looks dark in outer space Large Size (bigger than the Sun) 1. The outer layer of a star expands because of the decreasing gravitational force 2. It becomes a red giant and continues to expand and become a super red giant star 3. It finally explodes as a supernova producing large amounts of heat and light energy 4. The strong gravitational force in the core converts it to either a neutron star (from large star) or a black hole (from a super large star)
Page 6 of 6 Constellation - Group of stars that forms a certain pattern in the sky if an imaginary line is drawn - Some constellations are visible throughout the year (Ursa Major, Southern Cross) - Used as a compass and a calendar in ancient times - The Ursa Major and Southern Cross were used by sailors to navigate Galaxies - There are millions of galaxies in the universe and each galaxy : o contains millions of stars o has a different size and shape Type of Galaxies Elliptical Spiral Irregular The Universe - Defined as all of outer space & everything in it - Believed to have no end and contains thousands of millions of galaxies - Galaxies are scattered in the universe - Our solar system is in the Milky Way Galaxy The Milky Way - Our solar system is in the Milky Way Galaxy - It is spiral in shape and the Sun is one of the millions of stars in it - It has a thick centre and flat edges Additional Information - The Andromeda Galaxy is nearest to ours and the Milky Way is estimated to have about 10 000 000 000 stars - The Sun and other stars move around the Milky Way and takes about 200 million light years for the Sun to orbit the centre of the Milky Way