1. The Study of Light The Sun

2. Objectives 0 Explain how the sun produces energy which is transferred to the Earth by radiation. 0 Explain how incoming solar energy makes life possible on Earth

3. Properties of Stars 0 Star Birth – nebula 0 Protostar 0 developing star, not hot enough for nuclear fusion 0 Main-Sequence Stage 0 Main stage of the star (spends 90% of its time here) 0 Red-Giant Stage 0 The star expands as hydrogen is converted into helium 0 Burnout and Death 0 The star runs out of fuel and collapses due to gravity

5. Properties of Stars 0 White Dwarfs 0 Extremely small stars with extremely high densities 0 Neutron Stars 0 Smaller and more massive than white dwarfs 0 Diameter length of football field 0 Pea-size sample of this matter would weigh 100 million tons 0 Black Holes 0 Gravity so strong that even light can’t escape 0 Very hot

6. The Study of Light 0 Light behaves like waves and particles 0 Photons 0 Light acts like a stream of particles, which can push on matter. 0 Photons are able to push material away from a comet to produce a tail 0 Short wavelength – more energetic photons 0 Blue light has more energy than Red light

7. The Study of Light 0 Electromagnetic Radiation – light emitted from stars 0 This includes: 0 Gamma rays 0 X rays 0 Ultraviolet rays 0 Visible light 0 Infrared rays 0 Microwaves and Radar waves 0 Television and Radio waves

8. Structure of the Sun 0 Four parts: 0 Solar interior 0 Visible surface (photosphere) 0 Two atmospheric layers 0 Chromosphere 0 Corona

9. Structure of the Sun 0 Solar Interior 0 Nuclear Fusion 0 Energy is released by converting matter into pure energy 0 4 hydrogen nuclei are converted into the nucleus of a helium atom (releasing tons of energy) – core is made up of left over helium 0 Conversion of 1 pinhead’s worth of hydrogen to helium generates more energy than burning thousands of tons of coal. 0 Convection currents help transport this energy to the solar surface 0 The sun consumes an estimated 600 million tons of hydrogen each second

10. Structure of the Sun 0 E = mc 2 0 E (energy) = m(mass)*c(the speed of light) 2 0 The speed of light = 300,000 km/s 0 When hydrogen is converted into helium some of the mass is lost in the form of pure energy.

11. Structure of the Sun 0 Photosphere – visible surface 0 Radiates most of the sunlight we see 0 Consists of a layer of gas > 500km thick 0 Appears to be boiling as convection moves hot gasses to the surface. 0 Chromosphere – Observable during a total solar eclipse 0 Thin layer of hot gases a few thousand km thick 0 Causes the sun (sphere) to appear red

12. Structure of the Sun 0 Corona – outermost portion of the solar atmosphere 0 Very weak – only visible when the photosphere is covered 0 Extends a few million km from the sun (causes a glow)

13. Structure of the Sun 0 Sunspots – dark regions on the surface of the photosphere 0 Appear dark because their temperature is 1500K less than the surrounding solar surface. 0 Prominences – huge cloudlike structures consisting of chromospheric gases 0 Ionized gases trapped by magnetic fields that extend from areas of intense solar activity 0 Solar Flares – brief outbursts that normally last an hour 0 Release enormous amounts of energy in the form of ultraviolet, radio, and X-ray radiation 0 Aurora Borealis – occur in Earth’s upper atmosphere near magnetic poles

14. Key Points 0 How does the sun emit energy? 0 The sun is a huge ball of gas (hydrogen and helium). Gravitational attraction of all this mass creates enormous pressure in the interior that causes Nuclear Fusion, which releases energy. 0 How does the sun’s energy travel to Earth? 0 Energy is carried by photons (packets of light), only a small portion of which is visible. 0 Why is the sun’s energy important? 0 Solar energy makes life on Earth possible. This energy enables plants to grow, rain to fall, and wind to blow.