1. STARS!

2. Gravity is a force that pulls objects with mass toward each other. Gravity increases as mass increases, so the Sun has stronger gravity than the Earth. Gravity decreases as the distance between objects increases. Side Note on Gravity

3. A star is matter that emits huge amounts of energy. Stars are formed when: –clouds of dust and gas shrink under their own gravity –the dust collects together and splits into clumps. –as the cloud collapses, lots of heat is released due to nuclear fusion. Formation of star

4. The unit that is used to measure distance in the universe and between stars is the light year. A light year is distance that light travels in one year. Light travels 300 000 km/s. There are 31 536 000 seconds in a year. Distance = speed x time One light year = 9.46 x 10 12 km (this is equivalent to 2 billion Canadas laid end to end!!!)

5. The closest star (Alpha Centauri) to Earth is 4.3 light years away. This is 41 000 000 000 000 km away!!

6. Light years tell us how far back we are looking in time. The light from Alpha Centauri that we see tonight actually left the star 4.3 years ago! By looking at stars that are that are thousands or billions of light years away, astronomers can look back in time to see what the universe was like when it was younger.

7. Colour and Star Temperature The colour of stars tell us about their temperatures. ColourTemp Range (°C) Example Blue25 000 – 50 000 Zeta Orionis Bluish- white 11 000 – 25 000 Rigel, Spica White7500 – 11 000 Vega, Sirius Yellowish- white 6000 – 7500Polaris, Procyon Yellow5000 – 6000Sun, Alpha Centauri Orange3500 – 5000Arcturus Red2000 - 3500Betelgeuse

8. Galaxies A galaxy is a huge collection of gas, dust, and hundreds of billions of stars. The stars are attracted to each other by gravity and are constantly in motion. We are part of the Milky Way Galaxy.

9. Milky Way Galaxy Facts Contains –400 billion stars –our Solar System, –Dark Matter (does not reflect light) The Milky Way is disk-shaped Our Sun is located near the outer part of the disk Thicker inner region is called the central bulge – the whole galaxy rotates around this bulge.

10. Life of a Star Stars evolve from clouds of dust and gas and have a predictable series of stages: –Birth –Development –Death

11. Birth: –All stars begin in nebulas. A nebula is a huge cloud of dust and gas. –The dust swirls around and particles bump into each other. –Gravity pulls the particles together, and gets stronger as the clumps get bigger. –Nuclear fusion begins when the clumps are dense enough.

12. Major Part of Life: –During most of its life, a star uses nuclear fusion to produce energy. The time frame depends on the size of the star. Smaller stars will produce energy for a longer time. Old Age –During old age, a star uses up its hydrogen fuel and swells to a red giant. Death –When a star dies, its core collapses inwards creating a supernova.

13. Remains –Depending on size: Small stars will become a white dwarf, cool and fade Medium stars will have core material packed together as a neutron star Large stars will have core material pack together as a black hole

14. Types of Stars Red Giants: –Older stars that have swollen and cooled. White Dwarf: –Small star with a higher temperature than red or yellow stars. –Forms when a star dies: nuclear reactions are reduced the core shrinks outer layers drift away remaining material becomes a white dwarf

15. Neutron Star: –An extremely dense star composed of neutrons; happens when a star 10 times the mass of the Sun dies. Supernova: –An enormous explosion that occurs at the end of a star’s life. –Produces either a neutron star or a black hole.

16. Black Holes: –Small, very dense object with a force of gravity so strong that nothing can escape from it, not even light. –Happens when a star 30 times the mass of the Sun dies. –Very very dense. Has a very large mass.