1. What is an Atmosphere? A layer of gas which surrounds a world is called an atmosphere. What is the greenhouse effect?

2. © 2005 Pearson Education Inc., publishing as Addison-Wesley Greenhouse Effect on the Planets Greenhouse Effect warms Venus, Earth, & Mars on Venus: it is very strong on Earth: it is moderate on Mars: it is weak avg. temp. on Venus & Earth would be freezing without it

3. Planet Atmospheres Moon and Mercury: essentially airless with very little atmospheric gas Venus: thick CO 2 atmosphere, with high surface temperature Mars: thin CO 2 atmosphere, usually below freezing Earth: nitrogen/oxygen atmosphere with pleasant surface temperature

4. © 2005 Pearson Education Inc., publishing as Addison-Wesley Weather on Venus Today Dense atmosphere of mostly CO2 Prevents sun’s heat from escaping into space There is no rain on the surface. it is too hot and Venus has almost no H 2 O Clouds on Venus contain sulfuric acid Yellow clouds Gas released by volcanoes?

5. What are galaxies? Systems containing millions or billions of stars What galaxy does the Earth belong to? Milky Way

6. Types of galaxies SpiralEllipticalIrregular The Milky Way is a spiral galaxy. -bright star in middle with spiral of stars -stars concentrated in center -stars spread unevenly