Universe Celestial Object Galaxy Solar System

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2 ASTRONOMY Universe- Includes all known matter (everything). Celestial Object Any object outside or above Earth s atmosphere. Galaxy- A large group (billions) of stars (held together by gravity). Our galaxy is a spiral galaxy called the Milky Way. Our solar system is in one of the arms of the Milky Way. Solar System- The sun and all the objects that revolve it.

3 ORDER OF THE UNIVERSE Smallest to Largest: Planet Star Solar System Galaxy Universe

4 BIG BANG THEORY The Universe formed from an explosion called the Big Bang. It happened 10 to 14 billion years ago. The latest calculations now show that the universe is 13.7 or 13.8 billion years old. Most of the atoms were hydrogen and helium. The Universe has been cooling off ever since.

5 EVIDENCE OF THE BIG BANG THEORY Background Radiation Radiation has been found (microwaves) in all directions in the Universe. Doppler Effect (Electromagnetic Spectrum).

6 DOPPLER EFFECT - The universe is expanding. We know this because of the Doppler Effect. - The light from a star that is moving away from us will be shifted towards the red (infrared) end of the visible spectrum (Red Shift). Red light has a longer wave length. It is the space between the galaxies that is expanding. - A star that is moving towards us will be shifted towards the blue (ultraviolet) end (of the spectrum ( Blue Shift). Blue light has a short wavelength.

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11 STRUCTURE OF THE GALAXY Billions of stars held together by gravity. We are in the Milky Way Galaxy There are over 200 billion stars in our galaxy. It is a spiral galaxy (and it bulges in the center). We are located on one of the outer arms (ORION) on the left side. It is approximately 100,000 light years long.

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14 THE SUN Composed mainly of hydrogen. - Powered by nuclear fusion (hydrogen converting to helium). - The sun is an average star. It has average luminosity and temperature.

15 STARS A large ball of gas held together by gravity. Our Sun is an average star (medium mass). It is approximately 4.6 billion years old. It will live for about another 4.6 billion years. It is composed mainly of hydrogen (which is the most abundant element in the universe). Most stars live their lives on the Main Sequence. The HR Diagram (Classification of Stars Chart E.S.R.T.) is not a map. It is a classification system.

16 LIFE CYCLE OF A STAR THE MASS AT BIRTH DETERMINES THE PATH THE STAR WILL LEAD Most stars spend their lives on the main sequence.

17 LIFE CYCLE OF A STAR 1) Stars begin their lives as Molecular Clouds called Nebula. 2) Protostar: forms when a nebula is dense and cool enough to begin contracting into a star (GRAVITY). 3) When hydrogen begins to fuse into helium the protostar becomes a star (called Nuclear Fusion).

18 Solar System Also comets, asteroids, meteors H-R Diagram Classify stars by temp and luminosity Sun with planets revolving around it Nuclear Fusion powers the sun. Fusion = Lighter to Heavier Elements H H He He He C Sun has 6 layers Gas & Plasma

19 LIFE CYCLE OF A STAR 4) When stars use up all of their hydrogen they begin to fuse helium. The star expands, becoming a red giant. 5) When the helium is used up the star (Ex. Our sun) fuses carbon, the star is now a white dwarf. The star eventually runs out of fuel and burns out (becoming a black dwarf). 6) Large stars and binary stars may Supernova (blow up) instead of burning out. When they supernova a black hole or a neutron star might form.

20 OTHER STAR NOTES Luminosity of a star measures how bright it would be in relation to the sun if all stars were the same distance from an observer (Absolute magnitude). Apparent Magnitude This takes into account the absolute brightness and its distance from us. This is basically How the star looks to us at night. Light Year The distance light travels in a year (approx 6 trillion miles).

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23 LIFE CYCLE OF STARS

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26 SOLAR SYSTEM Consists of 8 planets and one star (Sun). 1) INNER PLANETS (Terrestrial Planets) Mercury, Venus, Earth, Mars Rocky surfaces High Density Low Mass 2)OUTER PLANETS (JOVIAN PLANETS) Jupiter, Saturn, Uranus, Neptune Gas Surfaces Low Density High Mass

27 PLANET NOTES Venus is the hottest planet due to the composition of its atmosphere - large amounts of Co2. Asteroid Belt - The area between Mars and Jupiter that contains asteroids or minor planets that orbit the Sun.

28 PLANET NOTES Evolution of the Solar System: Scientists believe that our solar system started to form approximately 4.6 billion years ago (see handout on beginning of the solar system). Astronomical Unit The distance between the Earth and the Sun (approximately 93 million miles). It takes about 225 million years for our solar system to move around the Milky Way Galaxy. Venus and Uranus rotate clockwise which is opposite of the other planets (counterclockwise).

29 Planets

30 SOLAR SYSTEM

31 OTHER CELESTIAL OBJECTS 1. MOONS bodies that orbit a planet (seen by reflected light only). 2. ASTEROIDS Rock fragments that revolve around the sun (most are in the Asteroid Belt). 3. COMETS Loose mass of rock, ice, dust, and gas that move throughout space together. 4. METEOROIDS Fragments of rock that travel through space. 5. METEORS Shooting Star meteoroid that has broken through our atmosphere. 6. METEORITE - chunk of rock that reaches Earth s surface.