Stars and the Universe
LIFE CYCLE OF A STAR:
-Show Me: Life Cycle of A Star
KEY CONCEPTS:
- The life cycle of a star is determined by its MASS. All stars begin in the Stellar Nebula also known
as the Stellar nursery. From there they enter into the Main Sequence which is the longest portion of
the star's life (10-80 billion years). Main sequence stars burn Hydrogen. Our sun is currently a Main
Sequence Star.
-If a star is around the same mass as our sun it will become a Red Giant after the main sequence
stage. During this stage the star expands as it begins to burn Helium. Eventually that Helium will float
out into space creating a Planetary Nebula.. Once the gasses have floated away all that is left is the
small core of the star which we call a White Dwarf. It glows very softly from the left over energy. Once
all of that left over energy is used up it no longer glows, it is dead, and called a black dwarf.
-Stars that are bigger than our sun become Super Red Giants after their main sequence stage.. Once
all of the helium is burned up the Super Red Giant explodes into a Supernova. Large stars will
become Neutron stars after the supernova. Neutron stars are very small (the size of an asteroid or
town on earth) but extremely dense. The most massive (HUGE) stars will become Black Holes after a
Supernova. A black hole is a
region of spacetime from which gravity prevents anything, including light, from escaping.
Here is a diagram of the life cycle of a star:
HR Diagram:
Show Me Video: HR Diagram
Scientists use the Herztsprung -Russell diagram to understand the relationship
between a star’s brightness and its surface temperature. On the Herztsprung Russell diagram there is a band known as the main sequence which contains about
90% of all stars. This shows that there is a strong relationship between a star’s
brightness and its surface temperature. The other 10% of stars are special types
(supergiants, giants, and white dwarfs), and each group falls in a distance area on
the diagram.
Apparent Magnitude: The brightness of a star as seen from Earth (The closer a star
the brighter it appears)
Absolute Magnitude: The "actual" brightness of a star. If all of the stars were placed
the same distance from the earth how bright they would be.
**Notice the X-axis is different on the HR Diagram than on most graphs. The Surface
Temperature is INCREASING as you move to the LEFT. The Absolute Magnitude
(Brightness) increases as you go up.
**Look at the graph and notice: The coolest brightest stars are red giants. The
hottest least bright stars are the white dwarfs. The main sequence stars follow the
general rule that the hotter the star the brighter it is :)
EM Spectrum:
Show Me Video: EM Spectrum
Key Concepts
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Key Concept 1: The electromagnetic spectrum is a range of all types of electromagnetic radiation. The
wavelengths range from very short wavelengths, including gamma and x-rays, to very long wavelengths, including
microwaves and radio waves. Radiation is energy that travels and spreads through space. As the electromagnetic
spectrum moves from long wavelengths to short wavelengths, the relative energy of the waves
increases. This means that long wavelengths have LESS energy and short
wavelengths have MORE energy.
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Key Concept 2: Radio waves have long wavelengths with low energy and carry data over long distances. They
are used in radios, televisions, cellular phones, and wireless networking. Radio waves are used to explore space,
such as with radio telescopes.
Key Concept 3: Microwaves have shorter wavelengths and more energy than radio waves. Recently, scientists
have discovered background microwave radiation left over from the early formation of the universe. This gives us
some idea about how far away other galaxies are from our galaxy.
Key Concept 4: Light waves have shorter wavelengths than microwaves and provide us with the visible light
spectrum – the colors that we see. Most stars emit energy in visible light waves. Since the speed of light is
constant, you can measure how long it takes for light to reach an object and then calculate the distance it resides
from that object.
Key Concept 5: Gamma rays are potentially dangerous waves with extremely short wavelengths and very large
amounts of energy. Solar flares and explosions of stars give off gamma rays. The radiation from gamma ray
bursts can be lethal to living things. Information about black holes and subatomic particles in space is studied
using gamma-ray telescopes.
Key Concept 6: The electromagnetic spectrum (EMS) can be utilized to evaluate distant components of the
universe to determine their movement relative to Earth’s position and location.
LIGHT YEARS: the way we measure distance in space. For smaller distances we
use Astronomical Units (AU) which is equal to the distance from the earth to the
sun.
Key Concepts
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Key Concept 1: Light travels at 300,000 kilometers per second. This is known as
the speed of light. It takes a ray of light about 8 minutes to go from the Sun to Earth.
Key Concept 2: Because of the vast distances between stars and other objects in
space, distances are measured in light years, which is the amount of distance light
can travel in one Earth year, or 365 days. It is a measure of distance, not time.
Key Concept 3: There is a time delay for images that are captured from objects in
space because light takes time to travel. Depending on the distance of the object
from the observer, by the time light enters through the lens of a telescope, it may
have been traveling for years.
ORIGINS OF THE UNIVERSE:
**In order from smallest to largest: Earth, Solar System, Galaxy, Universe-The earth,
other planets, and sun make up our solar system. Our solar system and others make up our galaxy
the Milky Way, galaxies combine to make up our universe.
There are 3 shapes of galaxies:
1. Spiral- Example: Milky Way (where earth is) and Andromeda
2. Elliptical- Example: M87 (Oval shaped with no arms)
3. Irregular- Example: Large Magellanic Cloud (No specific shape)
Theories on how Earth was Formed:
1. Big Bang: The idea that the whole universe is constantly expanding. Red
Shift (shows that most stars and planets are moving AWAY from earth)
supports this theory.
Key Concepts
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Key Concept 1: Because light travels at a known speed, we can take snapshots of
very distant wavelengths and determine the approximate age of the universe.
Key Concept 2: Evidence about the age of the universe can also be gathered by
studying how long certain known stars and other celestial objects took to form and
by measuring the speed at which galaxies are moving away from one another.
Key Concept 3: Scientists use a variety of methods to study the origins of the
universe, such as telescopes and maps of microwave radiation left over from the Big
Bang.
Key Concept 4: The Big Bang is a theory that says the universe began as a very
small and dense area that expanded rapidly. Data show that the universe is still
expanding.