Download Stars - cmamath

Objective-SWBAT:
Describe the life cycle of stars and be
able to diagram it.
Make and use an H-R diagram.
Define luminosity and magnitude.
Stars
A body of gases that gives off a
tremendous amount of energy in the
form of heat and light.
Star color
A clue to temperature
Red, orange, yellow, white and blue
Very hot = blue
Very cool = red
Medium = yellow (like our sun)
Size
Stars vary in size
Some stars are smaller than the sun.
The largest star is 2000 times larger
than our sun!
Sun’s diameter = 1,392,000 km
Composition
Hydrogen and helium are the two most
common elements found in stars.
Stellar Evolution
Stage 1: Nebulae
Cloud of gas and dust
70% H and 28% He
Dust is usually made of graphite,
diamonds, Si, carbide, and other
elements
Nebulae
Horsehead Nebula
Cat’s Eye Nebula
Stage 2: Protostar
Developing star; no nuclear fusion
Nebula contracts forming protostar
Very hot--10,000,000°C
Protostar
Stage 3: Main Sequence
90% of life spent in this stage
When the protostar is hot enough,
fusion begins
Stable during this stage
Will either become a large main
sequence star or a small main sequence
star (depending on mass)
Main Sequence
Stage 4: Red Giant or
Supergiant
Cooler surface gives a reddish appearance
Small main sequence stars become red giants
Large main sequence stars become
supergiants
A star enters this stage when all the H has
fused into He.
The star expands, then cools.
Red Giant
Our sun as a Red giant
Size comparisons
Stage 5: Burnout and Death
Death of a red giant
White dwarf: remains of low/medium mass
stars after nuclear fusion has completely
stopped.
After the white dwarf has completely
cooled, it becomes a black dwarf which is a
dead star that no longer shines.
White Dwarf
Death of a supergiant
Supernova: the star collapses and nuclear
fusion begins again (C into Mg into Fe)
The iron core collapses causing a brilliant
explosion
Next, the star can either become a black
hole or a neutron star
Supernova!
Black Hole
Formed from the collapse of large stars
Large mass contracted to an extremely
small size
Very, very dense
Gravity is so strong that even light
cannnot escape its pull.
Neutron Star
Mass left over from the explosion.
Smaller large main sequence stars.
Magnitude = brightness of a star
Apparent and Absolute
Magnitude
Apparent Magnitude
Describes how bright a star appears
from Earth.
Depends on the size of a star and its
distance from Earth.
Measured on a scale (-26.8 to +29)
Bright stars have low negative numbers
Sun is the brightest star in the sky
(apparent magnitude of -26.8)
Dimmest star in the sky has an
apparent magnitude of +29
The dimmest star seen with the
unaided eye is +6.
Anything dimmer must be
viewed with a telescope
Absolute Magnitude
True brightness
Describes how bright a star would
appear if seen from a distance of 32.6
LY
This is the distance that the brightness
would start becoming distorted.
Measured on a scale (-26.8 to +29)
Most stars have an absolute magnitude
between -5 and +5
Absolute magnitude of the sun is
+5
Stars less than 32.6 LY away
appear brighter than they really
are (low apparent magnitude and
high absolute magnitude.)
Sun is a perfect example. High
absolute magnitude (+5) and low
apparent magnitude (-26.8)
Stars more than 32.6 LY away
appear dimmer than they are
High apparent magnitude and low
absolute magnitude
If a star is 32.6 LY away, its
absolute and apparent magnitudes
will be the same.
Hertzsprung-Russell (H-R)
Diagram
Shows relationships between absolute
magnitude and temperature of stars.
Can also show the relationship between
temperature and luminosity
As temperature increases, brightness
increases and vice versa.
H-R Diagram