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ASTRONOMY NOTES 1. How is a planet different from a star? a. Planet doesn’t create its own light, Planet has weak source of energy, stars have no solid surface, stars made up of gas, planets mix of solid & liquids, planets smaller- less massive. 2. How many planets are known to exist? a. 8 major planets- (order closest to sun) Mercury, Venus, earth, mars, Jupiter, Saturn, Uranus, Neptune Solar system → sun, 8 planets, satellites of the planets, asteroids, comets, etc. 1. Why are so few craters on earth? b. Dense atmosphere, craters usually burn in atmosphere c. Most craters ever formed on Earth have been worn away by erosion (& other geological processes) d. moon 1/80 th mass of earth, only other planet to step on. i. Mars - smaller than earth, has polar cap, Olympus Mons (volcano) on mars, → larger at any other mountain in solar system! ii. Jupiter - is much larger than earth (10x diameter), largest in solar system, (“The Great Red Spot”- hurricane type weather.), rotates so fast clouds get stretched into bands, Jupiter has 2 moons (Io, Europa), Io is volcanically active. iii. Saturn- has ring, rings aren’t solid- atoms, rock, ice etc. make up rings. iv. Uranus- no cloud patterns looking at planet v. Neptune - blue, has some clouds and bands, has a cyclonic storm vi. Pluto - recently designated a dwarf planet vii. Sun-star (globe of gas)-Contains ⁿ/500 th of matter in solar system, 100x larger in diameter than earth, 300,000x more massive. Solar Neighborhood- (Milky Way Galaxy) 1. Light travels quickly! a. 186,000 miles/second, 7x’s around earth in 1 second, 1 foot in a billionth of a second. 2. Light travel time: a. Light second- 186,000 miles – 80% of distance to moon b. Light hour- 700 million miles- Distance from sun to Saturn c. Light year- 7 trillion miles- 1/4 th distance to nearest star i. Year- unit of time ii. Light year- unit of distance d. Almost all visible matter in universe are inside stars
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Solar Neighborhood- a. A “sea” of stars closest to the sun (w/in a few 100 ly) b. Several 10’s of thousands of stars c. Solar system very isolated from other stars 1. What is a galaxy?- cluster of stars 2. What is the name of our galaxy?- The Milky Way 3. Shape of our galaxy? - Fried egg, spiral galaxy, flattened spiral, flattened with a central bulge. a. Milky way diameter- 100,000 ly!, huge flattened system of several 100 billion stars b. earth→ solar system→ (Milky Way) Galaxy→ Local group→ Local Supercluster 4. How do stars move in the galaxy? - They revolve around the center, solar system takes 250 million years per orbit. (250 km/sec around galaxy)- solar system around galaxy 5. The Local Group- (a group of about 25 galaxies) a. Milky way- ours b. c. Andromeda Galaxy- similar to our structure d. NGC 300 6. Beyond Local Group- (several 1000 galaxies) a. Virgo Cluster 7. Local Supercluster- (about 10 galaxy clusters) a. The Local Group b. The Virgo Group 8. The Universe at Large:
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