Transcript I. Stars - SharpSchool

Stars
The Brightness of Stars
-Star: A luminous sphere of gas with enormous mass,
that produces energy by fusion.
-Fusion: The joining of separate nuclei. Common in
nature, but not on Earth.
Actual vs. Apparent Brightness
•
Variables which
affect a star’s
brightness:
1. Star size
2. Distance from Earth
3. Star temperature
• Apparent Brightness:
The amount of light
received on Earth
from a star.
• Actual Brightness:
How large and hot a
star is in relation to
other stars.
Star Brightness
• Example: Sirius has a
greater apparent
brightness then Rigel,
even though Rigel is
a much hotter and
brighter star.
• Why?
Lifecycle of Stars
video:
http://www.nationalstemcentre.org.uk/elibrary/resource/5415/the-life-cycle-of-stars
http://www.youtube.com/watch?v=4s7vyDLgk3M
http://www.enchantedlearning.com/sgifs/Starlifecycle.GIF
Star Lifecycle explained
“As space expands there are many
more gaps forming and they need to be
filled by stars and energy. So stars
need to have a dynamic life cycle.
Moments of birth and death, right? ”
http://library.thinkquest.org/C0110277/stars/life_cycle1.htm
Where are stars born?
• Nebula (stellar nursery):
Stars are born in
nebulae-- Huge clouds
of dust and gas
• Dust and gas particles
exert a gravitational
force on each other
which keeps pulling
them closer together.
• Orion Nebula
More Nebulas
• As the particles pull
closer together the
temperature increases.
• At 10,000,000o C
fusion takes place and
energy radiates
outward through the
condensing ball of gas.
• Another view of
Orion
Stellar Evolution – A sun-like star
http://www.enchantedlearning.com/subjects/astronomy/stars/lifecycle/sunlike.shtml
http://t1.gstatic.com/images?q=tbn:ANd9GcT_XJP25-_6XInCs2WJ2x3ramBhnntqYRcDHvFfj96_z1LHKO8kw
Huge Stars…
http://www.enchantedlearning.com/subjects/astronomy/stars/lifecycle/huge.shtml
Giant Stars…
http://www.enchantedlearning.com/subjects/astronomy/stars/lifecycle/giant.shtml
Nothing (even light) can escape the gravity of
a BLACK HOLE
Videos:
http://dsc.discovery.com/tv-shows/other-shows/videos/how-the-universe-works-birthof-a-black-hole.htm
http://www.space.com/15421-black-holes-facts-formation-discovery-sdcmp.html
http://dsc.discovery.com/tv-shows/other-shows/videos/stephen-hawkings-universeblack-hole-time.htm
Hertzsprung-Russell Diagram
http://aspire.cosmic-ray.org/labs/star_life/hr_diagram.html
Determining a Star’s
Temperature
• A star’s temperature can be determined by its color.
• All objects will glow a different color when heated differently
• Colors hottest to coolest: Blue/white  yellow  orange 
red.
Light-Years
• Light-year: Distance light travels in one year. (Equal to about
9.5 trillion kilometers)
• Approximate distances:
-Sun to edge of solar system = 5.5 light hours
-Nearest star (Alpha Centauri) = 4.3 light years
-Center to edge of Milky Way = 50,000 light years
The Sun and You
• Our sun is a main
sequence star
according to the
H-R Diagram.
• The actual
brightness is
average for a star
of its average size.
Layers of the Sun
• Dense inner core
which is the site of
hydrogen fusion.
• Radiation zone:
Energy bounces back
and forth before
escaping.
• Convections zone:
Cooler layer of gas
that is constantly
rising and sinking.
Anatomy of Sun
• Photosphere:
Bright source of
much of the light
we see.
• Chromosphere:
Active layer which
is home to many
significant
displays.
Anatomy of Sun
• Corona: Outer
layer which is a
gradual boundary
between sun and
space.
Sunspots
• Sunspots: Cool dark
areas on the sun’s
surface.
-First discovered by
Galileo
-Not permanent
features—Will
appear and
disappear
Cycle of Solar Activity
• Cycle of Solar
Activity: 11 year cycle
which see number of
sunspots change.
• Sunspot Maximum:
Time of many large
sunspots.
• Sunspot Minimum:
Time of few
sunspots.
Solar Flares
• Solar Flares: Violent
eruptions near a
sunspot which
suddenly brighten
and shoot outward at
high speed.
Solar Flares
• The interaction of solar flares with Earth’s magnetic field
causes the aurora borealis/ aurora australis
(Northern/Southern Lights)
Earth’s Galaxy—and Others
• Galaxy: A large group
of stars, gas, and dust
held together by
gravity.
• Milky Way: Our
galaxy which contains
about 200 billion
stars and many
nebulas
• Spiral Galaxies
Earth’s Galaxy—and Others
• Galaxies are grouped
together in clusters.
• The cluster the Milky
Way belongs to is
called the Local
Group.
• Three types of
galaxies:
• Cluster of galaxies
Elliptical Galaxies
• Elliptical Galaxies:
Most common type
of galaxy; large threedimensional football
shaped galaxies.
-Contain mostly
older and dimmer
stars.
Spiral Galaxies
• Spiral Galaxies:
Circular galaxies that
have arms curve
outward from a
central hub.
• Arms are made up
of stars and dust
• Two spiral galaxies!!
More Spiral Galaxies
• Barred spiral
galaxies: Have two
spiral arms extending
out.
Irregular Galaxies
• Irregular Galaxies:
Come in many
different shapes and
are smaller and less
common than
elliptical or spiral
galaxies.
The Milky Way Galaxy
• 100,000 light years in diameter
• Our sun orbits the center of the galaxy once every 240 million
years
• Probably a barred spiral galaxy
• Contains over 200 billion stars