Transcript Structure of the Universe

What is a galaxy?
• A collections of
billions of stars held
together by gravity
• There are billions of
galaxies
• Galaxies make up the
universe
What is the name our
galaxy?
• Milky Way- Why is it called that?
• Because we are on an outer arm of the
spiral (looks like a pin wheel) when you
look into it, it looks like a milky cloud.
What is a star?
A ball of gases held
together by gravity
which produces large
amounts of energy.
How do stars produce
energy?
Stars produce energy
by combining smaller
elements to form a
larger one,
specifically two
hydrogen atoms form
a helium atom,
What is luminosity?
Measure of how
bright a star would
be compared to the
sun, if they were
both the same
distance away from
an observer.
What is apparent
brightness?
• The apparent brightness is what we
observe when we look at stars.
• The apparent brightness depends on:
– How close it is
– How bright it actually is.
Star types
• Main sequence
– Average size
– As temperature increases, so does luminosity
• Giant stars
– Large, bright, cool stars
– Red, orange or yellow in color
– 10 or more times brighter then the sun
• Super giants
– High luminosity, high temperature
– 100 to 1000 times bigger then the sun
– Later in life; already a main sequence star
• White dwarfs
– Small, dim and hot stars
– Last shinning stage of a star
• Black dwarfs
– A white dwarf that cools and no longer gives off energy “dead
star”
Using the Reference tables
How would you classify our sun?
A main sequence star with a yellow
color and average size, and about
5,000-6,000 degrees in temperature.
What is the life cycle of a star?
What determines the
stages of star development?
The original mass of the star determines
its life cycle and how long it lasts.