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

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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

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Composition of the Atmosphere

Mixture of gases Nitrogen, oxygen, water vapor, and

many others 78% nitrogen, 21% oxygen, and 1%

others

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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

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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

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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

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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

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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

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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

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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

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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

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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