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Chapter 3 By Mrs. Shaw
Today’s astronomers use constellations to divide the sky into 88 regions.
Constellations are groups of stars, sometimes in patterns of animals, or objects.
Constellations are important because they can help define where in the sky astronomers are looking. (point of reference)
What are constellations and why are they important?
Lesson 1: The View from Earth
Remember that waves transfer energy. The amount of energy transferred has to do with the wavelength and frequency.
On one end of the spectrum are radio waves which have a longer wavelength and therefore transfer lower energy levels.
On the other end of the spectrum are Gamma rays which have a much shorter wavelength and higher frequency and therefore transfer energy at a much faster rate.
Review of Electromagnetic Spectrum
Spectroscopes Spectroscopes spread light into different wavelengths so
that astronomers can study a stars’ characteristics including temperature, compositions and energy.
Parallax is the apparent change in an objects position based on viewing it from different angles.
Astronomers use parallax angles to measure how far objects are in space.
Measuring distances in space
Measuring distances in space
Scientists use two different ways to measure distances in space: astronomical units and light years.
Astronomical units are used to measure distances within our solar system.
To measure much greater distances outside our solar system, scientists use light years. Light years are equal to the distance light travels in a year.
Actual measurements
1 AU = 149,598,000 kilometers (distance from Earth to Sun)
1 light year = about 9.5 to 10 trillion kilometers
• The sun is 109 times the diameter of Earth and about 8 light minutes away.
•Jupiter is about 40 light minutes away•Pluto is about 40 AU from the Sun or 5.5 light hours out•The next star is 4.5 light-years away!
•The center of the Milky Way is 25,000 light-years away.
Some perspective . . .
Measu
ring B
rightn
ess
Absolute Magnitude
The apparent magnitude of a star is the measure of how bright it appears from Earth.
Apparent Magnitude
The absolute magnitude of a star is the actual brightness of that star.
Scientists usually relate the brightness to the sun.
The term Luminosity is related to absolute magnitude.
As gravity pulls the cosmic dust in to create the star, atoms are colliding. When that happens with enough force the nuclei of the atoms combine and fuse during a process called nuclear fusion.
How do stars shine?
Lesson 2: The Sun and Other Stars
Interior of Stars
• Core: hydrogen is fused into helium, some massive stars have iron cores.
• Radiative Zone: shell of cooler hydrogen above the core
• Convection Zone: where hot gas moves up toward the surface and cooler gas moves quickly into the interior.
Atmosphere of Stars
•Photosphere: apparent surface of the star.
•Chromosphere: orange – red layer of a star’s atmosphere
•Corona: wide, outermost layer of star’s atmosphere. Highest temperature of all 3 atmospheric layers. (crown)
Composition of the SUN Know these layers!
Do these layers remind you of another structure you have learned bout?
As far as we currently know there is only one star in our solar system – the Sun!
Most stars exist in star systems bound together by gravity.
The most common system is a binary system where two stars orbit each other.
Stars also group in two types of clusters; open clusters and globular clusters.
http://imagine.gsfc.nasa.gov/docs/science/know_l1/binary_stars.html
Groups of Stars
GlobularCluster
OpenCluster
Binary
Stars are classified to learn about their past, composition, and future.
Stars can be classified by temperature, color, luminosity (brightness), and mass (size)
Classifying Stars
The H-R diagram classifies stars based on luminosity and temperature.
This classification helps scientists determine a stars approximate distance from Earth.
Hertzsprung-Russell Diagram
A. light years
B. kilometers
C. inches
D. astronomical units
Lesson 1 & 2 Review Game
1. What would an astronomer use to explain the distance from the Sun to the planet Neptune?
2. What is the difference between the terms astronomical unit and light year?
A. light years measure distances within the solar system but AU are used to measure distances outside it.
B. AU years measure distances within the solar system but light years are used to measure distances outside it.
C. light years are a much smaller number than astronomical units.
D. astronomical units are a much larger number than light years.
3. The term used to describe a stars actual brightness is . . .
A. apparent magnitude
B. brightosity
C. absolute magnitude or luminosity
D. constellation
4. Which answer has the terms in the correct order from smallest object to largest object?
A. planet, star, constellation, galaxy, universe
B. planet, star, constellation, universe, galaxy
C. star, planet, constellation, galaxy, universe
D. planet, constellation, star, galaxy, universe
5. The layer of the sun that we see from Earth is the . .
A. core
B. corona
C. photosphere
D. radiative zone
6. Which characteristic is related to a stars color?
A. mass
B. temperature
C. luminosity
D. composition
7. The layer of the sun where hot gas and cooler gas are circulated is ________________.
A. radiative zone
B. corona
C. photosphere
D. convection zone
8. Apparent magnitude is determined by
A. distance from Earth (or viewing point)
B. distance from the Sun
C. actual brightness or luminosity
D. color of star
9. When determining luminosity, a _______________ number has the most brightness.
A. higher
B. negative
C. positive
D. even
10. The chart used to classify stars based on absolute magnitude and temperature is a ______________________________. A. luminosity chart
B. main stage chart
C. H-R Diagram
D. constellation chart
Lesson 3: Evolution of Stars
All stars have a life cycle – a beginning and an end.
Stars lifespan depends mainly on their initial mass.
All stars are formed the same way.
All stars form deep inside a cloud of gas and cosmic dust called a nebula.
Gravity causes the densest parts to collapse, forming regions called Protostars.
Protostars continue to contract, pulling in surrounding gas, until their cores are hot and dense enough for nuclear fusion to occur.
The Birth of a Star
http://www.youtube.com/watch?v=4s7vyDLgk3M&feature=related
A star becomes a main-sequence star as soon as it starts fusing hydrogen into helium.
It stays a main sequence star until it runs out of hydrogen.
Lower mass stars last longer at this phase because they burn fuel at a slower rate then the high mass stars.
Main Sequence Stars
All stars start the same way but they don’t end the same way.
After Hydrogen is exhausted in core ...
1. Energy released from nuclear fusion counter-acts inward force of gravity.
2. Core collapses,
Kinetic energy of collapse converted into heat.
This heat expands the outer layers.
Meanwhile, as core collapses,
Increasing Temperature and Pressure
cause... . . . .
The Death of a Star
At 100 million degrees Celsius, Helium fuses.
Energy sustains the expanded outer layers of the Red Giant.
This is where the low to medium sized stars take a different path than the highest mass stars.
More FUSION!!
Supernovas can only happen when an aging massive star can no longer generate energy from nuclear fusion and undergoes a rapid gravitational collapse. This collapse releases potential energy that heats up and throws off the outer layers of the star in the form of an enormous explosion.
Higher Mass Star composition and fusion levels
White dwarf: are Hot, dense, slowly cooling spheres of Carbon.
Neutron Stars: Are dense cores of neutrons that remain after a Supernova.
Black Holes: Is an object whose gravity is so great that no light can escape.
What is left after a star dies?
At the end of a star’s life cycle, much of it’s gas escapes into space and into nebula where it will begin to clump together with other gases by gravity and eventually form new stars and planets again.
Recycling in the Universe
Galaxies are huge collections of stars.
The universe contains hundreds of billions of galaxies.
Lesson 4: Galaxies and the Universe
Matter that emits no light at any wavelength is called dark matter.
Scientists hypothesize that more than 90% of the universe’s mass is dark matter.
What is DARK MATTER??
Spiral Galaxies: have spiral arms that begin at a central disk. Spiral galaxies are thicker at the center, a region called the central bulge.
Elliptical Galaxies: shaped in a sphere or ellipse. Made of old red stars and contain little or no gas and dust.
Irregular Galaxies: are oddly shaped and contain many young stars and areas where lots of new stars are being formed.
3 Main types of Galaxies
Galaxies are not evenly distributed in the Universe. Gravity holds them together in groups called clusters.
Our Galaxy is the Milky Way Galaxy that is made of about 200 billion stars and about 30 different galaxies.
Scientists believe that our Milky Way Galaxy will eventually merge with the larger Andromeda Galaxy.
Groups of Galaxies
Scientists believe that the universe is 13-14 billion years old. In the beginning, the universe was very hot but it eventually cooled enough for atoms to form.
As atoms formed, stars and planets formed.
Scientists believe that space is expanding and stretching and objects are constantly moving away from eachother.
WHAT IS THEIR EVIDENCE BEHIND THIS BELIEF??
Origin and Expansion of the Universe
The Big Bang Theory
Doppler Shift
Dark Energy
How do Scientists measure movement of object in space?
The shift to a different wavelength that shows how light travels either towards or away from the observer.
Dark energy is a mysterious repulsive force that causes the universe to expand at an increasing rate.
