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Big Bang Theory Essential Question: How did our universe begin? Warm-up: Set up TOC for entirely new section –
Astronomy and for today: Big Bang Theory!
Today is an introduction…
• You only need to write a few notes – they are in red.
• Mostly, just pay attention and think while watching the videos and participating in the demos.
• We will do more investigations with Doppler Effect, wavelength, and visible light/colors later
Key Points of the Video all these are state standards – please write these notes!
• “Big Bang” is the currently accepted explanation of our universe.
• Big Bang was not an explosion
• “Expanding Universe Theory” is a more appropriate title!
Key Points of the Video all these are state standards – please write these notes!
• The universe is continually expanding and this started about 13.7 billion years ago.
• Evidence for this includes the “Red Shift/Blue Shift” data from Hubble.
References:
• Most of this information is from: Astronomy Today
• Please refer to this website if you would like more details:
http://www.astronomytoday.com/cosmology/bigbang.html
Big Bang Theory
• The universe, as we see it today, is expanding from a widely accepted theoretical event in space-time called the Big Bang that occurred approximately 13.7 billion years ago.
Our Expanding Universe
• We have observed that galaxy clusters, including our own, have been receding from each other.
• A common analogy applied to our expanding universe is of a spotted balloon being blown up.
• Make three dots on a balloon.
As the balloon is inflated, the dots move away from each other
Our Expanding Universe
• A similar thing happens in the universe, only in three dimensions.
• Ever since the Big Bang, the galaxies have been moving away from each other, but they are not moving away from any particular point.
• Instead, the space between the galaxies is stretching.
*please throw away your balloon so it doesn’t cause a problem in another class!
Are we moving also?
• Yes
• We watch the galaxies recede from us and believe ourselves to be stationary; however, this is just our relative view of the universe.
• Some galaxies do not recede from each other because their gravity holds them together. These are the galactic groups called 'clusters'.
Evidence?
• In 1929 Edwin Hubble, an American astronomer, discovered that galaxies all around us were receding, because light analyzed from each galaxy was red-shifted (the absorption lines were shifted to the red side of the spectrum, an effect known as the Doppler Effect, indicating that the light sources were moving away our galaxy).
• Edwin hypothesized that the further the galaxy, the faster its recession from earth; this became known as the Hubble Constant (Ho).
The Doppler Effect
• The Doppler Effect is the change in frequency of a wave for an observer moving relative to its source.
• This happens with both electromagnetic and mechanical waves.
• The animation below shows sound waves:
Doppler Effect
• As an object moves forward, waves are compressed
• Waves behind the object are elongated
• This change can be used to calculate distance and speed of moving objects (link to Carl Sagan below)
Try it yourself!
• Safety: only do this to yourself – no one else!
• Hold the tuning fork by the handle and gently tap it on the table.
• Bring it slowly to your ear and slowly move it away.
Big Bang – Day 2 Do Now:
• Collect Notebooks
• Pick Up “Expanding Universe” Prompt from front counter
• Please choose an answer off the “Expanding Universe” paper and write at least 1 sentence that supports your answer (Note – base your answer on the Big Bang Theory and what you think it states)
Doppler Effect & Wavelength • Please get your
notebook and review the notes from yesterday.
Waves - terms Sketch this diagram in your notebook
Frequency
• Frequency (of a wavelength) is how many complete waves go by a point per second
• EM waves move at a constant speed, but the frequency can change.
Types of waves
• Mechanical Waves need a “medium” to transmit energy
• Electromagnetic waves do not need a medium and are a combination of two waves that move together:
The Doppler Effect
• The Doppler Effect is the change in frequency of a wave for an observer moving relative to its source.
• This happens with both electromagnetic and mechanical waves.
• The animation below shows sound waves:
Doppler Effect
• As an object moves forward, waves are compressed
• Waves behind the object are elongated
• This change can be used to calculate distance and speed of moving objects (link to Carl Sagan below)
Try it yourself!
• Safety: only do this to yourself – no one else!
• Hold the tuning fork by the handle and gently tap it on the table.
• Bring it slowly to your ear and slowly move it away.
• Electromagnetic Waves have some different properties than mechanical waves, like sound and water waves, but they also can be changed by Doppler Effect.
• Notice that only a small band are visible to us as colors • Blue/violet waves have a shorter wavelength than the
orange/red waves
• If electromagnetic waves in the visible light band are longer or moving away so they appear to be longer, we see a color change.
• Moving away (making longer waves) causes a shift toward the red range.
• Shorter wavelength --------------longer wavelength
Red Shift • Different electromagnetic
wavelengths appear as different colors.
• Galaxies moving away from us have their wavelength stretched – it appears shifted to the longer wavelength colors – “red shifted”
• The further away a galaxy moves, the redder it becomes.
• Edwin Hubble is credited with this discovery! Click on Hubble
Red Shift/Blue Shift • Sketch this diagram in your notebook
• Discuss what is happening with a partner
RED
BLUE
Do we know everything about this?
• The structure of the universe is not fully known.
• Does it have any boundaries?
• Stephen Hawking believes the universe is boundless yet finite in size. One could keep on moving in one direction and eventually end up in the same place. As an analogy, if you walked in a straight line around Earth, you would eventually return to the same point at which you started.
“Background Radiation”
• Did you notice that longer electromagnetic waves are called “radio waves?” – they can be detected with electronic devices and transformed into sound:
“Background Radiation”
• Another phenomenon that is considered evidence of the “Big Bang” is “background radiation”
• This is a EM energy that is picked up from all areas of the universe.
• Most astronomers feel this is left over energy from the initial creation of our universe.
• There are many studies and lots of very technical reports about this!
“Expanding Universe”
• Think about the “Expanding Universe” paper – do you want to change your answer?
• Have you heard some ideas that support or go against your choice?
• The best answer is “B”
• The distance between the galaxies is expanding or stretching (like the balloon activity), but gravity holds the galaxies together, so they stay the same size.
Exit
• In your own words, explain why galaxies and stars moving away from our solar system appear red.
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