Tyler Brown
Fall 2012
Professor Jeff Adkins
Astronomy 010

FIRST SOURCE
Name of Page: The Doppler Effect
Summary: The Doppler effect occurs in sound, for example, when a train passes by and the pitch of the noise drops. This is because the wavelengths are different frequencies when the train is approaching you and moving away. The Doppler effect can also occur with light. The shift to shorter wavelengths with the Doppler effect in reference to the speed of light is called a "blue shift" while the shift to longer wavelengths with the Doppler effect in reference to teh speed of light is called a "red shift".
Name of Website: Astronomy 162, Stars, Galaxies, and Cosmology
URL: [[http://csep10.phys.utk.edu/astr162/lect/light/doppler.html]]
Author: Author unknown. Site apppears to be maintained by an indivual. The material seems to be trustworthy because it appears as if the site was set up by a teacher/professor for his students.
Last Updated: Unknown.
Date Reviewed: December 10, 2012.
Reviewed by: Tyler Brown.
Accuracy: Information seems up to date and accurate. Appears to be a study guide for students so I trust the source of the information is probably a textbook.
Readability and Clarity: Audience is students. The material is written well for students and is easy to comprehend.
Ease of Navigation: There are many more topics discussed on the website and it is easy to navigate around on and is in the simplest form that a website could be in.
SECOND SOURCE
Name of Page: The Doppler Effect and Sonic Booms
Summary: The Doppler effect was discovered by Christian Doppler in 1842. The Doppler effect is displayed when a jet plane flies faster than the speed of sound creating a cone which represents that jet flying faster than the speed of sound and creating a delayed "boom" because it takes the sound of the jet hitting supersonic speed longer to travel than the jet itself.
Name of Website: Acoustics and Vibration Animations
URL: [[http://www.acs.psu.edu/drussell/Demos/doppler/doppler.html]]
Author: Danielle A. Russell, Ph.D. Site is maintained by a university. The material is trustworthy considering that it is maintained by a school.
Last Updated: The exact date is unknown but the site is dated 2004-2011.
Date Reviewed: December 10, 2012.
Reviewed by: Tyler Brown.
Accuracy: The information is up to date and accurate.
Readability and Clarity: Audience is students. Easy to understand and does not require a high skill level to understand.
Ease of Navigation: The website is kind of easy to navigate around. It seemed to be linked to a different website which was confusing.
THIRD SOURCE
Name of Page: Explainer: the Doppler effect
Summary: The Doppler effect was discovered in 1842 by Christian Doppler when he observed that certain stars were either red or blue (due to the fact that they were either moving closer or further away creating a "blue shift" or a "red shift"). The Doppler effect has allowed us to understand many things in the universe and one day, the reversability of the Doppler effect could allow us to explore many new things only known in science fiction such as an invisibility cloak.
Name of Website: The Conversation
URL: [[http://theconversation.edu.au/explainer-the-doppler-effect-7475]]
Author: Gillian Isoardi. Site is maintained by a business perhaps. It appears so because there are advertisements.
Last Updated: July 3, 2012.
Date Reviewed: December 10, 2012.
Reviewed by: Tyler Brown.
Accuracy: The accuracy is questionable because the site appears to be a site for people to discuss things. However, none of the facts contradict any former knowledge that I have of the subject.
Readability and Clarity: The readability is very basic. The audience could be anybody from a 3rd grader to an adult.
Ease of Navigation: The page is fairly easy to navigate around. It has many other discussion topics and categories which are available at the top of the page.
FOURTH SOURCE
Name of Page: Doppler- Effect
Summary: The Doppler effect plays in important role in radar...in fact, radar would not exist without it. The way the Doppler effect works in radar is that wave lengths are transmitted from the radar to the object that is travelling at a certain speed. The wavelengths then bounce back and the number of wavelengths tell the radar how fast the object is travelling. This same process can also be used to determine if there is an object nearby within the reach of the radar.
Name of Website: Radartutorial .eu
UR: [[http://www.radartutorial.eu/11.coherent/co06.en.html]]
Author: Author unknown but the publisher is Christian Wolff. This website appears to be internationally maintained by multiple businesses.
Last Updated: Unknown.
Date Reviewed: December 10, 2012.
Reviewed by: Tyler Brown.
Accuracy: The site appears to be very accurate. There are many illustrations and links to other sites.
Readability and Clarity: The readability is normal. It seems to be best fit for college students but high school students would have no problem understanding it.
Ease of Navigation: The website is mainly a website for radar use/radar technology so I can't exactly navigate it successfully because I am not knowledgable in the subject.
FIFTH SOURCE
Name of Page: The Doppler Effect
Summary: The Doppler effect is best described as the change in picth of a sound that it moving towards or away from the ovserver. This explains that change in pitch of a moving race car engine or police sirens. Edwin Hubble used the Doppler effect to discover that the universe was expanding.
Name of Website: Windows to the Universe
URL: [[http://www.windows2universe.org/earth/Atmosphere/tornado/doppler_effect.html]]
Author: Becca Hatheway. The website is maintained by a business which is known because of the many advertisements.
Last Updated: June 11, 2010.
Date Reviewed: December 10, 2012.
Reviewed by: Tyler Brown.
Accuracy: The material is up to date and accurate. There are no flaws in the facts.
Readability and Clarity: The readability is incredibly basic. This site gives the most basic description of the Doppler effect and is very brief but informative.
Ease of Navigation: The website is easy to navigate around. There are also many additional extra things on the website that make it unique.

The Doppler Effect


The Doppler effect is the change in frequency of a wave that is moving further or closer to the observer. The Doppler effect is named after Christian Doppler who proposed the idea of it in 1842. In 1848, Hippolyte Fizeau discovered the same effect on electromagnetic waves independently.

Most people are familiar with the Doppler effect even if they don't know about it. That is because most people have observed it with sound waves as an object got closer or farther from them. When an object moves toward the observer the sound waves bunch up increasing the frequency and raising the pitch. As the object moves away from the observer it causes the sound waves to be further apart lowering the frequency and lowering the pitch.

ambu.jpg
Image demonstrating different wave lengths
Source:http://www.geography.hunter.cuny.edu/

In astronomy, the Doppler effect can be used to see if objects are moving closer to or further away from us. As an object in space moves closer to us, the light waves become bunched up causing the object to appear slightly bluer in color. This is called a blue shift. As an object moves further away, the waves become further apart causing the object to appear slightly redder than it should be. This is called a red shift.
shift.png
Image demonstrating red and blue shifts
Source:http://aha-moments.com/2008/08/the-momentum-of-social-networks-part-4-doppler-shift/


By using the Doppler effect, astronomers have learned that all galaxies (excluding the ones in our local group) are getting further away as they show a red shift. This is called the cosmological red shift and is evidence that the universe is expanding. On the other hand, the galaxies in our local group show a blue shift as they are all getting closer to each other. This is due to the fact that they are close enough that gravity is stronger then the expansion. Our Milky Way galaxy and the Andromeda galaxy are getting closer and chances are they will collide but not until 3 to 4.5 million years. The Sagittarius Dwarf Elliptical galaxy is a galaxy orbiting our Milky Way galaxy and is estimated to eventually pass through the galactic disk. The Sagittarius Dwarf Elliptical galaxy is also slowly being absorbed into our galaxy.

http://www.physicsclassroom.com/class/waves/u10l3d.cfm
describes the Doppler effect in a pretty easy to understand form. seems like a good place to learn how waves behave or any other physics related things as the website is about teaching people about physics. the site seems to be ok and would be updated if needed so there is no need to worry about it being outdated. overalll a good site for those who want to learn how the physics work.

http://archive.ncsa.illinois.edu/Cyberia/Bima/doppler.html
a site containing a small bit of info on the Doppler effect. the explanation should be good enough that a person not knowing too much should be able to understand the information. the website contains a few other things about astronomy. the only problem is that it was last updated in 1995. the info about the Doppler effect should be ok but the other info might be outdated.

http://galileoandeinstein.physics.virginia.edu/more_stuff/flashlets/doppler.htm
a flash application that shows how the wave frequency changes as on object moves closer or further from an observer. to use it drag the mic image to a location then click the button that makes the source move left or right. you can also change the speed of the object in terms of mach number. this app uses sound so when a wave hits the mic you will here a clicking sound. shows how that as an object aproches an observer hears the noise it makes with a higher pitch and frequency and as it gets further away with a lower pitch and frequency.
the link in the bottom links to the lecture notes related to the app and contains the math on how it works for those interested.
as the lecture notes are dated 10/14/09 that means its fairly recent but i don't expect there to be many if any updates.

http://astro.unl.edu/classaction/animations/light/dopplershift.html
a flash animation that shows the change in frequency in a wave. to use it just let it load then click start emission and either move the ball named S which stands for source or the ball named O which stands for observer. on the top it shows the wave sent from the source which is constant and under that is the wave that the observer observes as it or the source moves.
the simulator is easy to use. the main website (http://astro.unl.edu/) is full of simulators and other helpful things for those trying to improve their knowledge of astronomy.
overall a great site. last updated on April 6th, 2010

http://www.youtube.com/watch?v=Kg9F5pN5tlI
A 2 minute video by Blaine Greenhalgh explaining the Doppler effect. uploaded on youtube in 2008 so it's fairly recent. the video itself makes it easy to understand the Doppler effect and requires no reading so its good for those who don't like to read or are visual learners. i like it. about as good as Bill Nye