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AstronomyChapters 24, 25 and 26
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Ch 24.1: The Atmosphere
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
3
Atmosphere continued…
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
4
Composition of the Atmosphere
Mixture of gases Nitrogen, oxygen, water vapor, and
many others 78% nitrogen, 21% oxygen, and 1%
others
5
Pressure
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
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Layers of the Atmosphere
4 primary layers Troposphere,
stratosphere, mesosphere, and thermosphere
Layers are divided by variations in temperature
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Troposphere
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
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Stratosphere
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
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Mesophere
The layer above the stratosphere
Altitude from about 50km to about 80 km
Temperatures decrease with increasing altitude
Meteors generally burn up here
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Thermosphere
Upper or outer most layer
Altitude from about 80km into space without boundary
Temperatures increase rapidly with increasing altitude
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The Ionosphere
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
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The Ionosphere continued…
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25.1 Exploring the Solar System 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
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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
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25.2 The Earth-Moon System 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
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Moon continued…
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
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Phases of the moon
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
18
Tides on Earth
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
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Spring Tide and Neap Tide 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
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26.2 Stars
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)
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Properties of stars
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
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Properties of Stars continued…
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
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Properties of Stars continued…
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
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A Sample Spectrum with Absorption Lines
A solar spectrum with dark absorption linesThis line indicates the element sodiumThese lines indicates the element Mercury
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Properties of Stars continued…
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
26
Hertzsprung-Russell Diagram 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
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H-R Diagram
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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
Types of Stars on the H-R diagram
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26.3 Life Cycles of Stars
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
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Star Formation
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
31
Adult stars
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
32
26.5 The Expanding Universe 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
33
The Big Bang Theory
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
34
After the Big Bang
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
35
Evidence for the Big Bang Theory
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
36
Age of the universe
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
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The Dark Side
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
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What will happen in the future?
Will galaxies rush apart forever or collapse?
These are questions physicists and scientists have been, and are still trying, to answer