1. Chapters 24, 25 and 26

2.  The atmosphere is the layer of gases that surrounds Earth.  Forms a protective layer between Earth and space  Provides conditions suitable for life as we know it  Protects Earth from meteors, chunks of rock and metal, and from high-energy radiation 2

3.  Holds in heat and helps moderate Earth’s temperature  Without it Earth’s surface would be like the moon; boiling hot during the day and freezing at night  Provides gases essential for life 3

4.  Mixture of gases  Nitrogen, oxygen, water vapor, and many others  78% nitrogen, 21% oxygen, and 1% others 4

5.  Air pressure is the force exerted by the weight of a column of air on a surface  Air pressure changes with altitude  Atmosphere is densest near Earth’s surface and less dense as altitude increases because air can be compressed  Air pressure is greatest where the air is densest  So…as altitude increases, air pressure and density decrease 5

6.  4 primary layers  Troposphere, stratosphere, mesosphere, and thermosphere  Layers are divided by variations in temperature 6

7.  Lowest layer  Contains all the living things and most of the water vapor and suspended particles  Most weather takes place here  Height ranges from 9km at the poles to 16 km at the tropics with an avg. of 12km  Temperatures generally decrease with increasing altitude 7

8.  Above the troposphere  Altitude of about 12km to about 50km  Upper stratosphere is warmer than the lower part because of the ozone layer, which absorbs ultraviolet radiation from sunlight  Ozone layer is important for life because UV radiation can be harmful to life  Chemical pollutants can deplete the ozone layer, but ozone levels have mostly stabilized recently 8

9.  The layer above the stratosphere  Altitude from about 50km to about 80 km  Temperatures decrease with increasing altitude  Meteors generally burn up here 9

10.  Upper or outer most layer  Altitude from about 80km into space without boundary  Temperatures increase rapidly with increasing altitude 10

11.  Not a distinct layer of the atmosphere but a region in the Thermosphere  Region of charged particles (ions) that overlaps lower thermosphere  Mostly at altitudes of 80km to 400km  Nitrogen and oxygen lose 1 or more electron as they absorb solar radiation  Where the aurora occurs 11

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13.  2 primary models of the solar system: Geocentric Model and Heliocentric Model  Geocentric Model says that the Earth is stationary and objects in the sky move around it. Accepted for nearly 1400 years  Heliocentric Model says Earth and other planets revolve around the sun. Developed by the Greek astronomer Aristarchus. Mostly not accepted. Theory revived in early 1500’s by Copernicus. Proved by Galileo’s observations 13

14.  Our solar system is made up of the sun, planets, moons, and a variety of smaller objects  In 1600 Johannes Kepler (German mathematician) discovered that planets orbit the sun not in a circle, but an ellipse  Gravity and inertia (tendancy of an object to resist change in its motion) keep planets in their orbits 14

15.  Earth’s moon has very weak gravity  Gas molecules are not held in place with gravity so they float off into space-Moon has no atmosphere  The lack of an atmosphere means that the moon’s surface temperature varies from very hot during the day (about 130 ° C or 266 ° F) to very cold at night (about -180 ° C or -356 ° F)  Liquid water evaporated 15

16.  The major features of the moon are  Maria-low flat plains formed from lava flows  Highlands-rough mountainous regions covering most of the moon  Craters-round depressions from meteoroids  Hypothsis is that the moon formed from a collision early in Earth’s history 16

17.  Phases are the different shapes of the moon visible from Earth  Caused by changes in the relative position of the moon, sun, and Earth as the moon revolves around the Earth  Eclipses occur when the shadow of one body falls on another  Solar Eclipse occurs when the moon casts a shadow on the Earth  Lunar eclipse occurs when the Earth casts a shadow on the moon 17

18.  Tides are the regular rise and fall of ocean waters  Tides are caused mainly by the differences in the moon’s gravitational pull on Earth  The gravitational pull causes the oceans to bulge  The sun also has a gravitational effect, but it is about half of the moon’s effect 18

19.  Spring Tide- Occurs during a full moon  The Earth, sun and moon are in a straight line and the sun and moon’s gravitational effect are added together  Change between daily high and low tides are the greatest  Neap Tide- When the sun and moon are pulling the Earth at right angles  Change between daily high and low tides are the least 19

20.  Most of the universe is empty space  Stars are separated by vast distances measured in light-years  A light-year is the distance light travels in a vacuum in one year (about 9.5 trillion km) 20

21.  There are many different types  Stars are classified by their color, size, and brightness. Chemical composition and mass are also important.  Color indicates temperature. Blue is hottest, then yellow then red 21

22.  The brightness of a star does not necessarily tell you how close it is  Apparent brightness is how bright a star appears from Earth  Absolute brightness is how bright a star actually is and does not depend on its distance from Earth 22

23.  Astronomers calculate mass by observing gravitational interactions  Astronomers use a spectrograph to identify elements in the star’s atmosphere  Spectrographs spread out the light into a spectrum containing absorption lines. The lines indicate the presence of various elements 23

24. A solar spectrum with dark absorption lines This line indicates the element sodium These lines indicates the element Mercury 24

25.  Most stars have a chemical makeup similar to the sun, with hydrogen (H) and Helium (He) together making up 96 to 99.9% of the star’s mass 25

26.  One of Astronomy’s most important tools is the Hertzsprung-Russell Diagram (H-R Diagram)  Discovered in the 1900’s through observations by two different astronomers  Graph of the surface temperature (color) and absolute brightness  Used to estimate the sizes of stars and their distances and to infer how stars change over time 26

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28.  Main sequence stars- 90% of stars. The diagonal band on the H-R diagram  Supergiants- very bright stars at upper right of diagram  Giants- large bright stars that are smaller and fainter than supergiants  White dwarf- small, dense, hot but dimmer than main sequence stars of same temperature 28

29.  Stars change over time  Most stars are on the main sequence  About 10% are white dwarfs  Less than 1% are giants or supergiants  Space around stars contains gas and dust 29

30.  Nebula- large cloud of gas and dust spread over a large volume of space  Protostar- a contracting cloud of gas and dust with enough mass to form a star  A star is formed when a contracting cloud of dust and gas becomes so dense and hot that nuclear fusion begins 30

31.  Stars spend about 90% of their lives on the main sequence  A star’s mass determines the star’s place on the main sequence and how long it stays there  The decreasing supply of fuel in a star’s core eventually leads to its death as a white dwarf, neutron star or black hole 31

32.  Hubble’s Law- The speed a galaxy is moving away from us is proportional to its distance from us.  Light from most galaxies undergoes red shift- their light is shifted toward the red wavelengths  Red Shift shows us that nearly all galaxies are moving farther away from Earth  Red shift is one way that we know the universe is expanding 32

33.  Astronomers theorize that the universe came into being at a single moment, in an event called the big bang  All matter and energy in the universe was concentrated in a hot and small area  About 13.7 Billion years ago 33

34.  The universe expanded quickly and cooled  First stars and galaxies formed about 200 million years after the big bang  Solar system formed about 4.6 billion years ago 34

35.  In 1965 Penzias and Wilson discovered the existence of cosmic background radiation produced during the big bang  The red shift of galaxies indicating they are moving away from us  Einstein’s theory of general relativity  Currently the best explanation of available evidence 35

36.  Astronomers calculate the age of the universe based on how fast it is expanding now  Based on these calculations astronomers estimate the universe if 13.7 billion years old 36

37.  Much of the matter in the universe can’t be seen. It is Dark matter  Although it can’t be seen its presence can be detected by observing its gravitational effects on visible matter  Astronomers don’t know what it is made of or how it is distributed  Much of the universe may be dark matter  Dark energy is also theorized to exist 37

38.  Will galaxies rush apart forever or collapse?  These are questions physicists and scientists have been, and are still trying, to answer 38