Transcript Scientists classify stars by

STARS
Instructions
• Students will underline the portions of the
PowerPoint that are underlined.
A Nuclear Furnace
1. A star is like a gigantic nuclear furnace.
2. The nuclear reactions inside convert
hydrogen into helium by means of a
process known as fusion.
3. It is this nuclear reaction that gives a star
its energy.
Classifying Stars
Scientists classify stars by:
1.Temperature
2.Brightness
Star Temperature
1. The color of a star tells us about its
temperature.
 Blue stars are the hottest, 7500°C30,000°C.
 Red stars are the coolest, less than
3500°C.
 Our sun is yellow in color, in the
middle of the temperature scale,
from 5000°C-7500°C.
BetelgeuseRed StarCoolest
RigelBlue Star-Hottest
CONSTELLATION ORION
Brightness or Magnitude
1. Stars are also classified by their brightness.
2. The brightness of a star as seen from Earth is
called apparent magnitude.
3. The actual brightness of a star is called absolute
magnitude.
Example: The SUN has an absolute magnitude
of 4.8 when compared to the other stars. The
SUN has an apparent magnitude of -26.8
because it is so close. The lower the number the
brighter the star.
Another Example of absolute and
apparent magnitude.
B
Which light is brighter, A or B?
A






Light A is brighter than light B.
We see the apparent magnitude of the lights
(how they look to us)
If lights A and B were next to each other they
would look the same because the two lights are
exactly the same.
Their absolute magnitude is the same.
Distance makes them look different. The same
is true for stars.
Two stars could be the same brightness but their
distance from us makes their brightness
different.
H-R Diagram
Brighter
1. The H-R Diagram
shows us color, size,
temperature, absolute
magnitude and the life
cycle of stars.
Dimmer
Hotter
Cooler
Life Cycle of A Star
1. Stars begin their lives as clouds of dust and
gas called a stellar nebula.
A Protostar
The gravity of a passing star or the shock wave
from a nearby supernova may cause the nebula
to contract.
1. Matter in the gas cloud will begin to come
together into a dense region called a protostar.
2. As the protostar continues to condense, it heats
up.
3. Eventually, it reaches a critical mass and nuclear
fusion begins.
4. This begins the main sequence phase of the star.
Our Sun is a main sequence star.
PROTOSTAR
Main Sequence Stars
1. The life span of a star depends on its
size.
2. Very massive stars will become blue
giants during their main sequence.
Their main sequence may last only a few
hundred thousand years.
3. Smaller stars, like the Sun, will burn for
several billion years during their main
sequence stage.
4. Our Sun is in its main sequence.
The main sequence is the longest part of a star’s life
Average sized
star like our
Sun during
main sequence.
Massive star larger
than our Sun during
main sequence
Red Giant and Red Supergiant
1. Eventually, the star's fuel will begin to run
out.
2. Our Sun will expand into what is known
as a red giant.
3. Massive stars will become red
supergiants.
4. This phase will last until the star exhausts
its remaining fuel.
5. At this point, the star will collapse.
Our Sun
1. Most average stars will blow away their
outer atmospheres to form a planetary
nebula.
2. Their cores will remain behind and burn
as a white dwarf until they cool down.
3. What will be left is a dark ball of matter
known as a black dwarf.
Planetary Nebula
White Dwarf
Massive Stars
1. If the star is massive enough, the collapse will
trigger a violent explosion known as a
supernova.
2. If the remaining mass of the star is about 1.4
times that of our Sun, it will collapse further to
become a neutron star.
3. If the remaining mass of the star is more than
about three times that of the Sun, it will collapse
and what is left behind is an intense region of
gravity called a black hole.
Massive Stars (Larger than our Sun)
Become Red Supergiants.
Red Supergiant becomes Supernova
in a giant explosion,
OR It becomes a Black Hole
This is an illustration, not an actual
black hole!!
Supernova Becomes a Neutron Star
Life Cycle of our Sun
1.
2.
3.
4.
5.
6.
7.
Stellar Nebula
Protostar
Main Sequence
Red Giant
Planetary Nebula
White Dwarf
Black Dwarf
Life Cycle of a Massive Star
Stellar Nebula
2. Protostar
3. Blue Giant
4. Red Supergiant
5. Supernova
6. Neutron Star
(Pulsar)
OR
7. Black Hole
1.
Interactive Website
• http://aspire.cosmicray.org/labs/star_life/starlife_main.html