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
H-R Diagram
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
3. Giants and Dwarfs
a. Very bright 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, which are the small,
dense remains of a low- or mediummass 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
Brightness of a Star
The actual “brightness” of a star depends
upon 3 things: actual size of the star,
temperature, and distance from Earth
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
iii. Light and heat
both travel this
way from a star
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 gas
b. Gravity pulls the small pieces of
dust to clump together & form a
protostar
2. 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 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
The path a star takes in its life
cycle depends on its size/mass
3. LARGE MASS STARS : Results in
huge, bright explosion called a
supernova
a. Supernova produce heavier elements up to
the element iron.
The path a star takes in its life
cycle depends on its size/mass
http://www.youtube.com/watch?v=xsfie0Ly
0Ic&NR=1&feature=fvwp
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 of the visible
light spectrum
b. http://www.youtube.com/watch?v=FhfnqboacV0
c. http://www.youtube.com/watch?v=3k
w4id0NvJ0&NR=1&feature=fvwp
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
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
What force is responsible for
causing interstellar material to
condense and form our sun?
GRAVITY
3. Evidence for the Bang
a. Red 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
4. What is the future of our
universe?
a. It all depends on the mass of our
universe
b. One of 3 things can happen:
i. Universe can continue to expand
ii. Universe can stop expanding and remain
constant
iii. Universe can collapse in on itself (“Big
Crunch”)
What causes the moon to
“shine?”
It’s actually a reflection of the sun’s light
off the surface, back to the earth.
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
and Earth as the moon revolves
around the Earth [Fig 8, p.634]
2. http://aspire.cosmicray.org/labs/moon/lunar_phase3.swf
http://www.sumanasinc.com/webcontent/animations/content/moonphase.html
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 vs Lunar Eclipses
http://www.youtube.com/watch?v=XMyqPx
Fh5Zw
http://www.youtube.com/watch?v=nXseT
WTZlks&feature=related
http://www.youtube.com/watch?v=wHxcW
SiD_4E
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
The Milky Way- our galaxy is a
spiral galaxy