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Stars
What are stars?
Stars are giant spheres of superhot gas
made up mostly of hydrogen and helium.
Stars get so hot by burning hydrogen into
helium in a process called nuclear fusion.
Nuclear fusion is what makes them so hot
and bright.
Constellations
A constellation is a group of stars that
appear to form a pattern in the sky.
The stars in a constellation often have
no relationship to each other in space.
Properties of Stars
Astronomers classify stars by their
color, SIZE, and brightness.
Other properties include chemical
composition and mass.
A Star’s Color and Temperature
A star’s color indicates the temperature of its’ surface.
The HOTTEST stars appear BLUE
The COOLER stars appear RED
The spectrum of color in a star is from blues to greens to yellows to reds.
Properties of Stars
Mass- The single most important property that
determines other properties of the star.
Luminosity-(Brightness)-the total amount of light
energy that a star gives off into space.
Temperature- surface temperature, closely
related to the luminosity and color of the star.
Spectral Type- closely related to the surface
temperature.
Size-together with temperature determine the
luminosity.
Brightness of Stars
The brightness of a star viewed from Earth is dependent on a few things.
Color intensity
Distance
Apparent Brightness- is the brightness of a star as it appears from Earth.
Absolute Brightness-How bright the star really is-not dependent on distance.
Composition of Stars
Each star has its own color spectrum.
Most stars have a chemical make-up that is similar to the Sun, with hydrogen and helium making up most of the star’s mass.
Stars all start out the same way:
Stars start out in a giant cloud of interstellar dust,
hydrogen, helium gas, and plasma called
nebulae (nebula is singular).
Life Cycle continued
Sometimes part of the cloud shrinks
because of gravity.
As more and more dust gathers and
gravity gets stronger, the accumulation of
dust and gravity will create a protostar.
Once the center gets hot enough, nuclear
fusion will begin and a young star is born!
Main Sequence Star
Nuclear fusion keeps the star from collapsing.
A star will continue to burn energy and glow for billions of years.
This is the “state” of the star for the majority of its life and is called the “main sequence.”
During this time there is a balance (equilibrium) between gravity wanting to shrink the star and heat wanting to make it grow bigger.
The star will remain this way until it runs out of hydrogen.
Life Cycle to the END…
Average Star vs. Massive Star Death…
Classifying Stars
Two scientists, Ejnar Hertzsprung and Henry Russell made
discovery in the early 1900’s that in general, stars with
higher temperatures also have brighter absolute
magnitudes.
They developed a graph to show the relationship.
They placed temperature across the bottom and
absolute magnitude (increasing brightness) up one side.
It is known as the H-R diagram.
Most stars fit into a diagnol band that runs from the
upper left to the lower right of the graph. This band is
called the “main sequence.”
H-R Diagram
Neil DeGrasse Tyson explain a Black
Hole
https://www.youtube.com/watch?v=h1iJXOUMJpg#t=175