All about the Stars
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The distances to stars are very large
so astronomers use light years as units.
A light year is the distance light can travel in one year.
1 light year = 9.5 trillion kilometers or 5.8 trillion miles.
(Light travels at a rate of 300,000 km per second.)
A stars brightness is controlled by 3 factors:
1. The size of the star
2. The temperature of the star
3. The distance from the viewer (this is the most important one)
Absolute Magnitude/Luminosity = The true brightness of a star
Apparent Magnitude = How bright a star appears to us on Earth
As the Earth’s distance from a star increases, it’s apparent magnitude
Stellar Evolution (How stars form)
In outer space there is plenty of material, but it is very spaced out.
Over time, gravity begins to pull this material together. Hydrogen is
the most common element that gets pulled in by gravity.
Eventually large, dark, cool clouds of matter form. Because of the
mass increase, gravity begins to contract the cloud further. The
temperature begins to rise and the cloud radiates heat (infrared). This
is a Protostar (infant star).
The gravity contraction continues, and the star reaches 10 million K.
Hydrogen nuclei begin to fuse (join together). This is called
Nuclear Fusion or Hydrogen Fusion. The hydrogen turns into
Helium when it fuses.
A star is formed by hydrogen fusing into helium. This is what all
stars are made of and why they continue to burn and explode today.
Take out page 15 in your Earth Science Reference Tables.
Let’s compare the two charts. Mrs. Degl
The Life Cycle of the Stars (the short summary)
All stars are born in the Red Dwarf Phase. Stars are coolest at this
point and relatively small. Stars stay in this phase for a few million
As they grow, they enter the Main Sequence Phase. This phase has a
temperature range from 5,000 ºC to 16,000 ºC. Stars that are born
small will have a lower temperature than stars that are born larger.
Stars stay in this phase for about 9.5 billion years. Larger stars will
leave this phase quicker than smaller stars.
After the Main Sequence, larger stars now enter the Blue Supergiant
phase. These are the largest stars. The smaller/medium stars will
enter the Red Giant after leaving the Main Sequence.
Now on to the death of stars………
How Stars Die Out
(very short summary)
The Blue Supergiants will begin to burn up all of the hydrogen that
they have after a few million years. When this happens, the outer
shell of the star begins to expand. It grows to about triple the size
that it currently is. The Blue Supergiant now becomes a
Supergiant. Supergiants are orange/yellow and are mostly helium.
This is the last stage before it blows up. Blue Supergiants can have
one of two fates. They will Supernova (explode) and become a
Neutron Star or a Black Hole. Only the high mass stars can do
these two things.
The small/medium stars have a completely different death.
After staying put in the Main Sequence stage for a a while, they
also run out of hydrogen, and expand to the Red Giant stage.
This is also about three times the size of the original star. Once
the small/medium stars run out of gas, they will Nova and end
up as White Dwarfs. In this stage, the stars slowly burn out.
These can form after a Supernova. A major explosion causes all of
the star matter to contract together. All of this contraction creates an
area of extremely high gravity and density. A pea sized sample of
neutron star would weigh 100 million tons. It is like taking each
person in the world and combining them into an area the size of a
sugar cube. These have very strong magnetic fields and can turn into
stars, called Pulsars, which emit radio waves, in a pulse like manner.
These are more dense than a Neutron Star. The intense surface
gravity does not allow light to escape. All surrounding matter is
pulled into it. These areas give off X-rays. That is how we can
Crab Nebula - Neutron Star
The relative sizes of the planets compared to
The Pillars of Creation
Eagle nebula, a nearby star-forming region 7,000 light-years
from Earth in the constellation Serpens.
Mountains of Creation
The Spitzer image shows the eastern edge of a region known as W5, in the
Cassiopeia constellation 7,000 light-years away. This region is dominated by a
single massive star, whose location outside the pictured area is "pointed out" by
the finger-like pillars. These pillars themselves are colossal, together
resembling a mountain range. These are more than 10 times the size of those in
the Pillars of Creation, in the Eagle Nebula.