Download Exploring the Universe

I.) Properties of Stars
A. Color and Temperature
1. A star’s color indicates that temperature
of its surface
a. Hottest stars (surface temps above
30,000K) appear blue
b. Milder stars (surface temps between
5,000-6,000K) appear yellow
c. Relatively cool stars (surface temps
~3,000K) appear red
B. Hertzsprung-Russell Diagram: a graph of
the surface temperature (or color) and
absolute brightness of a sample of stars
1. H-R diagrams are used to estimate the
sizes of stars and their distances, and
to infer how stars change over time
a. Horizontal axis=surface temperature
b. Vertical axis=absolute brightness
2. Main-Sequence Stars
a. Main sequence: A line or sequence in
an H-R diagram where most stars
spend 90% of their life.
i. A diagonal band running from the
bright, hot stars on the upper left to
the dim, cool stars on the lower right
ii. Example: The Sun lies in the main
sequence
iii. The sun is a yellow star (medium
sized) that does fusion of hydrogen
to helium
3. Giants and Dwarfs
a. Very bright/cool stars in upper right of
H-R diagram are known as
supergiants
i. Very large (100 to 1000 times the
diameter of the sun)
b. Just below the supergiants are the
giants
c. Below the main sequence are the
white dwarfs (hot/dim), which are the
small, dense remains of a low- or
medium-mass star
D. Energy From Stars
1. Energy moves through the layers of a
star by combination of convection,
conduction, and radiation
a. Convection: rising hot gas moves
upward, away from the star’s center,
and cooler, denser gas sinks toward
the center
b. Conduction occurs when energy is
transferred from individual atom to
individual atom
c. Radiation occurs when energy
radiates out from the star in the form of
light
i. Travels at the speed of light
ii. Light from Sun
takes 8 minutes
to reach Earth
II.) Life Cycle of Stars
A. How Stars Form
1. Nebula: a large cloud of dust & gas in
interstellar space
a. Composed of mainly hydrogen &
helium
b. Gravity pulls the small pieces of
dust to clump together & form a
protostar
2. When a protostar is dense & hot
enough it will begin fusion. Nuclear
fusion begins to take control over
the gravity and the star begins to
stabilize.
a. Fusion reactions in the core
produce an outward force that
balances the inward force of
gravity
B. Adult Stars
1. Most stars spend 90% of their life
in main sequence
2. Once achieving nuclear fusion,
stars radiate energy into space
C. The brightness of a star depends
on its distance from earth, size,
and temperature
C. The Death of a Star
1. When the hydrogen fuel has run out &
fusion can no longer continue, the star
collapses because the forces are no
longer balanced
2. Core collapses because of its own
gravity & then rebounds with a shock
wave that violently blows the star’s outer
layers away from the core
3. Results in huge, bright explosion called a
supernova
a. Supernova
produce
elements
heavier than
iron (like gold
or lead)
Some Definitions
• Universe- the sum of all space, matter, &
energy that exists, that has existed in the
past, & that will exist in the future
• -everything physical that exists in space
& time
• Galaxy- a collection of stars, dust, & gas
bound together by gravity
• Solar System- the sun & all of the planets
& other bodies that travel around it.
III.) Expanding Universe
A. Hubble’s Law
1. Edwin Hubble used observations of
spectral lines from other galaxies to
conclude that the universe is
expanding
a. Lines shifted toward the red end
(longer wavelengths) of the visible
light spectrum
Electromagnetic Spectrum
2. Red shift: the apparent shift toward
longer wavelengths of light caused when
a luminous object moves away from the
observer
a. Red shift showed that nearly all
galaxies are getting farther away from
Earth
3. Blue shift: an apparent shift toward
shorter wavelengths of light caused
when a luminous object moves towards
the observer
4. The red/blue shift help us to better
understand the Doppler Effect
B. Big Bang Theory
1. The Big Bang Theory states
that all matter and energy in
the universe was compressed
into an extremely small volume
that 10 to 20 billion years ago
exploded and began
expanding in all directions
3. Evidence for the Bang
a. Red shift, blue shift, and cosmic
background radiation
b. Cosmic background radiation: steady,
but very dim signals in the form of
microwaves that are emitted all over
the sky
i. Scientists believe that these
microwaves are the remains of the
radiation produced during the Big
Bang
IV.) Phases of the Moon &
Eclipses
A. The different shapes of the moon visible
from Earth are called phases
1. Moon’s phases are caused by
changes in the relative positions of
the moon, sun, and Earth as the
moon revolves around the Earth [Fig 8,
p.634]
The “Big Crunch”
• The varying theories of the universe’s
eventual fate all depend upon the
universe’s current mass
• The evidence that the universe is
expanding makes some scientists believe
that everything will collapse one day upon
itself and result in the “big crunch”
Phases of the Moon
• The moon is able to be illuminated due to
the sun’s light reflecting off of its surface
• As the moon revolves around Earth, the
illuminated portion of the side of the moon
facing Earth changes.
• When the moon is full, the earth is
between the sun and moon and the half
that faces you is lit.
• When the moon is new, the side that is
facing you is dark, so you can’t see it.
B. Eclipse: an event in which the shadow of
one celestial body falls on another [Fig 9,
p.635]
1. Caused by the changes in relative
positions of the moon, sun, and
Earth—when all three are lined up in a
certain order
2. Solar Eclipse: Moon blocks the sun
3. Lunar Eclipse: Earth’s shadow blocks
the moon
Solar Eclipse
Solar Eclipse: Moon blocks the sun and
causes a shadow on the earth
As seen from the Earth, a solar eclipse
occurs when the Moon passes between the
Sun and the Earth, and the Moon fully or
partially covers the Sun as viewed from some
location on Earth. The sky will turn dark as
the moon blocks out the sun.
Lunar Eclipse
A lunar eclipse occurs when the
moon passes behind the earth such
that the earth blocks the sun’s rays
from striking the moon. This can occur
only when the Sun, Earth and Moon
are aligned exactly, or very closely so,
with the Earth in the middle.
Hence, there is always a full moon the
night of a lunar eclipse & it passes into
the Earth’s shadow. All observers on
the night side of earth can see the full
moon darken
Lunar Eclipse: Earth’s
shadow blocks the moon
C. Tides
1. Caused by the differences in the pull of
the moon’s gravity on different areas of
the Earth
2. Coastal areas have two high tides and
two low tides each day
a. Times of the tides will vary because
the moon is orbiting around the Earth