Properties of Waves All electromagnetic waves travel at the same speed The speed of light: 300,000,000 m/s trough crest
Wavelength (length/cycle) Wavelength ( ): the length of one complete cycle trough crest Properties of Waves All electromagnetic waves travel at the same speed The speed of light: 300,000,000 m/s
Wavelength (length/cycle) Amplitude : 1/2 height between trough and crest Amplitude trough crest Properties of Waves All electromagnetic waves travel at the same speed The speed of light: 300,000,000 m/s
Wave Speed = wavelength x frequency Wave Speed = f (length/second) = (length/cycle) x (cycle/second)
Light as a Wave Light waves are characterized by a wavelength and a frequency f c = 300,000 km/s = 3 10 8 m/s l
Light as a Wave Wavelengths of light are measured in units of nanometers (nm) or Å ngstr öm (Å) : 1 nm = 10 -9 m 1 Å = 10 -10 m = 0.1 nm Visible light has wavelengths between 4000 Å and 7000 Å (400 nm – 700 nm) .
The Electromagnetic Spectrum Need satellites to observe Wavelength Frequency High flying air planes or satellites
Wavelengths and Colors D i f f e r e n t colors of visible light correspond to different wavelengths.
Visible Light (VIS) 700 to 400 nm Our eyes are sensitive to this region of the spectrum Red - Orange - Yellow - Green - Blue - Indigo - Violet
Solar Radiation The Source for 99.9% of Earth’s Energy
Solar Spectrum The sun emits radiation at all wavelengths Most of its energy is in the IR - VIS - UV portions of the spectrum ~50% of the energy is in the visible region ~40% in the near-IR ~10% in the UV Wavelength (m)
Have the longest wavelengths and lowest frequencies of all the electromagnetic waves.
A radio picks up radio waves through an antenna and converts it to sound waves.
Each radio station in an area broadcasts at a different frequency. # on radio dial tells frequency. MRI (MAGNETIC RESONACE IMAGING)
Uses radio waves with a magnet to create an image
Microwaves —have the shortest wavelengths and the highest frequency of the radio waves.
Used in microwave ovens.
Waves transfer energy to the water in the food causing them to vibrate which in turn transfers energy in the form of heat to the food.
Used by cell phones and pagers.
RADAR ( Ra dio D etection a nd R anging)
Used to find the speed of an object by sending out radio waves and measuring the time it takes them to return.
Infrared = below red
Shorter wavelength and higher frequency than microwaves.
You can feel the longest ones as warmth on your skin
Heat lamps give off infrared waves.
Warm objects give off more heat energy than cool objects.
Thermogram —a picture that shows regions of different temperatures in the body. Temperatures are calculated by the amount of infrared radiation given off. Therefore people give off infrared rays.
Shorter wavelength and higher frequency than infrared rays.
Electromagnetic waves we can see.
Longest wavelength= red light
Shortest wavelength= violet (purple) light
When light enters a new medium it bends (refracts). Each wavelength bends a different amount allowing white light to separate into it’s various colors ROYGBIV.
Shorter wavelength and higher frequency than visible light
Carry more energy than visible light
Used to kill bacteria. (Sterilization of equipment)
Causes your skin to produce vitamin D (good for teeth and bones)
Too much can cause skin cancer.
Use sun block to protect against (UV rays)
Shorter wavelength and higher frequency than UV-rays
Carry a great amount of energy
Can penetrate most matter.
Bones and teeth absorb x-rays. (The light part of an x-ray image indicates a place where the x-ray was absorbed)
Too much exposure can cause cancer
(lead vest at dentist protects organs from unnecessary exposure)
Used by engineers to check for tiny cracks in structures.
The rays pass through the cracks and the cracks appear dark on film.
Shorter wavelength and higher frequency than X-rays
Carry the greatest amount of energy and penetrate the most.
Used in radiation treatment to kill cancer cells.
Can be very harmful if not used correctly.
All electromagnetic waves travel at the same speed. (300,000,000 meters/second in a vacuum.
They all have different wavelength and different frequencies.
Long wavelength- lowest frequency
Short wavelength highest frequency
The higher the frequency the higher the energy.
Light as Particle
Light also behaves like a particle
This particle is called a photon
The energy of a photon is dependent on its frequency
A photon is like a little packet (quantum) of electromagnetic energy.
Where do photons come from?
Photons come from atoms
Atoms absorb and emit photons at certain specific frequencies.
This is because the electrons can only be in certain orbitals.
Atomic Emission e -
Atoms of an specific element absorb or emit only specific frequencies of electromagnetic energy.
This is called the absorption or emission spectrum.
Using this in astronomy
Astronomers can use these spectra to determine the composition of stars and planets and other stellar objects.
The Sun’s Emission Spectrum
Wave particle duality
Light can also behave light particles called photons.
These photons come from the electrons in atoms.
Because electrons can only be in specific orbitals, only specific frequencies are emitted or absorbed.
These specific frequencies (spectrum) can be used to determine what elements are present.
Using wavelength/frequency to determine composition
Can use light emitted
Or light absorbed
Light and temperature
Electromagnetic spectrum also tells temperature
More heat = more energy
More energy = higher frequency
Higher frequency = More heat
electromagnetic radiation emitted an object because of the object's temperature
Temperature of Stars
Gamma and x-ray emitters are hottest
Blue stars are hotter
Red stars are colder
Radio emitters are coldest
Kelvin is the astronomer’s temperature scale
Abbreviation : K
K= ºC + 273
So… 0K = -273ºC
What’s colder than cold?
Absolutely NO atomic motion
No not even a little.
Deep space is just a few degrees above absolute zero
Spectroscopy is using electromagnetic radiation to determine composition
Thermal radiation is electromagnetic radiation emitted due to temperature
This can be used to determine the temperature and composition of stellar objects
Absolute zero (0K) is no atomic motion
Manipulating, or working with, light is what astronomers do
We have two main ways to manipulate light:
Changing the direction of light as it passes through some medium
Straw in drink
Focus light through a series of lenses
Like what Galileo used
Redirection of electromagnetic radiation
Can be done with more than just visible light!
Focus light through a series of mirrors
Invented by Isaac Newton
Allow for larger telescopes
English astronomer William Herschel built this huge reflecting telescope in the late 1700s.
Work like visible light reflector scopes
Use the radio frequencies
Cassiopeia in visible light
Cassiopeia A in radio
Light hitting an object causes electrons to be released