Electromagnetic Spectrum and what it points to

Waves Properties Review• Amplitude

– “…is the maximum distance that the particles of the medium carrying the wave move away from their rest positions” (Pasachoff 13).

• Wavelength– “…the number of meters needed for the wave to repeat itself at a given

moment of time” (McMillan 45).• Frequency

– “…is the number of complete waves that pass a given point in a certain amount of time” (Pasachoff 13).

scienceaid.co.uk

Doppler Effect

– “The change in frequency of a wave as its source moves in relation to an observer is called the Doppler effect” (Pasachoff 46).

– The change in frequency is heard through pitch/sound

– When the source move towards the observer the frequency increase as the wave move closer together (wavelength decreases)

– When the source moves away from the observer the wavelength gets longer and the frequency decreases

Electromagnetic Waves

• Transverse wave made up of electrical and magnetic energy• It is produced when the electric and magnetic fields switch

back and forth (vibrating) causing a disturbance that travels through space as a wave.

• This wave carries energy and information from one part of the universe to another, which is called electromagnetic radiation.

• Our instruments pick up these electromagnetic waves and change them into vibrating tunes/static

• Travel at the speed of light: 299,792.458 km/s in a vacuum

Electromagnetic Spectrum

• “All electromagnetic waves travel at the same speed in a vacuum, but they have different wavelengths and different frequencies” (Pasachoff 75).

• “…is the complete range of electromagnetic waves placed in order of increasing frequency” (Pasachoff 75).

• Radio waves, Infrared rays, Visible light, ultraviolet rays, X-rays, and gamma rays.

• Radio Waves– Longest wavelength and lowest frequencies– Broadcast waves and microwaves

• Infrared Rays– Wavelength shorter than radio waves– The invisible heat you feel

Visible Light

• You can see• The longest wavelengths and lower

frequencies appear in the red and the shortest wavelengths and higher frequencies appear in the violet/blue

• Violet Blue Green Yellow Orange Red

• Ultraviolet rays– Shorter wavelengths and higher frequencies than visible light– They carry more energy than visible light– Pros: killing bacteria and providing vitamin D– Cons: to much exposure causes skin cancer, can damage your eyes, and

burn your skin• X-Rays:

– Shorter wavelengths and higher frequencies than ultraviolet rays, thus can carry more energy

– Can go through most matter, except dense matter like bones• Gamma Rays:

– Have the shortest wavelength and highest frequencies, thus has the greatest amount of energy

– Great penetrating ability– Pros: use to kill cancer cells inside the body, use to help see inside the

body– Cons: nuclear reactions produce and can be harmful (even deadly if

exposed to too much).

Spectrographs

Activity 2

• http://www.learner.org/teacherslab/science/light/color/spectra/

• Draw the different spectrum for each element in your science journal

• Violet Blue Green Yellow Orange Red

• Sodium

Spectral Line Analysis

Activity 3

Study the following.

Spectrums A, B and C are from identical stars within our galaxy. Spectrum A represents a possible spectrum of a star not moving toward or away from Earth. Spectrums B and C show stars in motion with respect to an observer on Earth. Compare the three spectrums and answer the following questions:

Questions

1. What is the approximate range in nanometers that the black lines fall in for A? for B? for C?

2. Which spectrum is that of a star moving toward Earth? 3. Which spectrum is that of a star moving away from Earth? 4. In comparison to A, which is moving faster, B or C? Using data, justify your answer.

Distant Galaxy Spectrums

Activity 4

Galaxy Wave length (cm) Light-years away 21.00 21.10 21.20 21.30

Stars in the Milky Way ІІ

A few light-years 21.00 21.10 21.20 21.30Ursa Major ІІ

1,000,000,000 21.00 21.10 21.20 21.30Corona Borealis ІІ 1,400,000,000 21.00 21.10 21.20 21.30

Bootes ІІ 2,500,000,000 21.00 21.10 21.20 21.30

Hydra ІІ 3,960,000,000 21.00 21.10 21.20 21.30

With the advent of new microwave detectors, hydrogen was found to emit 21.00 cm wavelengths of “light”. This wavelength of “light” belongs to the microwave region of the electromagnetic spectrum. Below are presented spectral data taken from stars in our own galaxy and of far-away galaxies. Each spectrum only shows information collected in the microwave (21.00 – 21.30 cm) region of the electromagnetic spectrum where the characteristic dark lines of hydrogen are found. The microwave “light” given off by hydrogen is shown as the two dark bands in each of the spectrums below. These spectrums have been redrawn from the actual spectra of hydrogen measured in a laboratory to enhance their clarity.Questions:1. Make a chart below that contains the name of each galaxy and the approximate wavelength reading for the hydrogen emission “dark bands” in that galaxy. 2. Based on your understanding of the Doppler Effect, what two things can you infer from these spectrums? Use the data to defend your conclusions.

The Big Inference

Activity 5

Hubble’s Discovery

• “Just as the light from a single star can be used to make a stellar spectrum, scientists can also use the light given off by an entire galaxy to create the spectrum for that galaxy” (Holt 793).

• In the 1920s, Hubble found that the spectra of galaxies, except a few near our own, where all shift towards the red end of the spectrum.

• By measuring the redshift he was able to determine the speed at which the galaxies were moving away from us.– Most distance galaxies show the greatest speed and redshift

• This evidence point to the fact that our universe was expanding.

• Most galaxies are red-shifted, or moving away from us today. Let’s rewind the clock of time. Using the information and data from what you have learned, what can be inferred about the origin of the universe?

Rescores

• Allison, Mead A. Ph. D, DeGaetano, Arthur, T. Ph. D, and Pasachoff, Jay, M. Ph. D. Earth Science. Holt, Rinehart and Winston. 2006.

• Maggio, Deanne, Exploring the Spectrum. Bountiful Junior High.

• McMillan, Chasisson, Astronomy: a beginners' guide to the Universe. Pearson Education, Inc., St. San Francisco CA 2010 6th edition.

• Pasachoff, Jay M. Ph.D, Sound and Light: Science Explorer, Prentice Hall. Upper Saddle River, New Jersey. 2005