Download Chapter 19 I. The Sun, Earth and Moon A. Sun is our closest star B

Chapter 19
I. The Sun, Earth and Moon
A. Sun is our closest star
B. Everything revolves around the Sun
C. Planets and distant stars are visible in the night sky
D. Earth is part of Solar System
E. Gravity holds the solar system together
1. We usually think of gravity as the attractive force that pulls us to
the Earth.
2. True definition of gravity is the attractive force between objects.
3. The more mass an object has the greater its gravitational pull.
a. The Sun has more mass than any object in the solar system
b. tides are caused by the moon’s gravitational pull on the
Water on the Earth
b. everything in solar system orbits around Sun
F. The Moon
1. Moon doesn’t orbit the Sun directly
a. orbits the Earth
i. due to this the moon has phases
2. How was the moon formed?
a. Earth collided by large body & part of the Earth “broke off”
i. ejected material clumped together
ii. moon began to orbit the Earth
3. Evidence?
a. composition of the moon is the same as the Earth’s
4. Phases of the moon
a. phases of the moon are not caused by Earth’s shadow
b. also see book page 634
5. Eclipses
a. occur when Earth, Moon and Sun line up…….SOLAR ECLIPSE
b. lunar eclipse
Formation of the Solar System
Nebular Model of Space Formation
A. according to this theory the solar system is about 4.6 billion years old.
B. See transparency A
II. During this process small celestial bodies also formed
A. Comets- long tails and icy centers
1. orbits around Sun usually very long
B. Asteroids- made from different elements
C. Meteorites- sometimes strike the Earth
Chapter 20
I. The Life and Death of Stars
A.
What are stars?
1. Stars are huge spheres of hot gas that emit light and other radiation
2. they are driven by nuclear fusion reactions
a. may take millions of years for energy to make its way through
B. Why are some stars brighter than others?
1. depends on star’s temperature, size and distance from earth
C. How do we get information about stars
1. LIGHT
a. the wavelengths ( including those out of the visible spectrum) tell us all about
the composition of the star
i. stars color tell us its temperature
*blue stars are the hottest
*red are the coolest
ii. spectral lines tell us what kinds of elements the stars are made of
D. The fate of stars
1. Remember the sun formed from a cloud of gas and dust
2. It now has a balance of inward and outward forces
3. AS fusion slows, the pressure in the core will drop and contract this will cause the
outer layers to expand
a. the sun will become a RED GIANT
4. After about 100 million years the core will run out of helium and will contract further
which will cause outer layers to expand further.
a. the sun will then become a WHITE DWARF
i. about the size of earth
5. Supergiants- very massive star
1. evolve faster than smaller stars
2. core is iron
a. iron cannot fuse together to make heavier element
b. put more energy in than is given out……..endothermic reaction
c. star will explode……supernova
d.. after this explosion either a neutron star (very massive, but only few
kilometers large) thimble full of a neutron star has more mass than 100 million times the
earth
e. or a black hole will form (matter so massive and compressed not even
light can escape it)
6. H-R Diagram shows how stars evolve
1. compares the temperature to the brightness
II. Origin of the Universe
A. Universe- everything physical that exists in space and time
B. We see the universe now as it was in the past
1. Recall we get information about the stars from light
2. It takes time for light to travel the enormous distances it needs to get to us
3. By the time this light reaches us, the star may no longer be there
C. Most of the universe is empty space
D. What do we know about the Universe?
1. The universe is EXPANDING
2. Doppler effect
a. Red shift……object coming closer to us
b. Blue shift……moving away
E. Future of the Universe
1. Future is uncertain
a. 3 possibilities….depends on the total amount of matter in the universe
i.
Keep expanding forever…not enough mass, gravitational
forces too weak to stop expansion
ii. Universe stop expanding……just right amount of mass…will
slow but never stop completely
iii. Universe stop expanding and fall back in on itself…..more mass
than gravity will overcome this expansion and the universe
will start to contract
*eventually this contraction could collapse into a single point
in space (big crunch)……maybe the universe will end or
maybe start all over with another big bang
2. Universe contains dark matter….scientist don’t know how much or how to
detect
3. Scientists are using math to build better models