What is Light?What is Light?
Properties of WavesProperties of Waves
All electromagnetic waves travel at the same speedThe speed of light: 300,000,000 m/s
trough
crest
Wavelength
(length/cycle)
Wavelength (): the length of one complete cycle
trough
crest
Properties of WavesProperties of Waves
All electromagnetic waves travel at the same speedThe speed of light: 300,000,000 m/s
Wavelength
(length/cycle)
Amplitude: 1/2 height between trough and crest
Amplitude
trough
crest
Properties of WavesProperties of Waves
All electromagnetic waves travel at the same speedThe 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 WaveLight as a Wave
Light waves are characterized by a wavelength
and a frequency f
c = 300,000 km/s = 3108 m/s
ll
Electromagnetic WavesElectromagnetic Waves
Light as a WaveLight as a WaveWavelengths of light are measured in units of
nanometers (nm) or Ångström (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 SpectrumThe Electromagnetic Spectrum
Need satellites to observe
Wavelength
Frequency
High flying air planes
or satellites
Wavelengths and ColorsWavelengths and Colors
Different 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 SpectrumSolar 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)
RADIO WAVESRADIO WAVES Have the Have the longestlongest wavelengths and wavelengths and
lowest lowest frequencies of all the electromagnetic waves.frequencies of all the electromagnetic waves. A radio picks up radio waves through A radio picks up radio waves through
an antenna and converts it to an antenna and converts it to sound waves.sound waves.
Each radio station in an area broadcasts Each radio station in an area broadcasts at a different frequency. # on radio at a different frequency. # on radio dial tells frequency.dial tells frequency.
MRI MRI (MAGNETIC RESONACE IMAGING)(MAGNETIC RESONACE IMAGING)
Uses radio waves with a Uses radio waves with a magnet to create an imagemagnet to create an image
MICROWAVESMICROWAVES MicrowavesMicrowaves—have the shortest wavelengths —have the shortest wavelengths
and the highest frequency of the and the highest frequency of the radio waves.radio waves. Used in microwave ovens.Used in microwave ovens.
• Waves transfer energy to the water in the food causing Waves transfer energy to the water in the food causing them to vibrate which in turn transfers energy in the them to vibrate which in turn transfers energy in the form of heat to the food.form of heat to the food.
Used by Used by cell phones and pagers.cell phones and pagers. RADARRADAR ( (RaRadio dio DDetection etection aand nd RRanging)anging)
• Used to find the speed of an object by sending out radio Used to find the speed of an object by sending out radio waves and measuring the time it takes them to return.waves and measuring the time it takes them to return.
INFRARED RAYSINFRARED RAYS InfraredInfrared= below red= below red Shorter wavelength and higher Shorter wavelength and higher
frequency than microwaves.frequency than microwaves. You can feel the longest ones You can feel the longest ones
as warmth on your skinas warmth on your skin Heat lamps give off infrared Heat lamps give off infrared
waves.waves. Warm objects give off more Warm objects give off more
heat energy than cool objects.heat energy than cool objects. ThermogramThermogram—a picture that —a picture that
shows regions of different shows regions of different temperatures in the body. temperatures in the body. Temperatures are calculated by Temperatures are calculated by the amount of infrared radiation the amount of infrared radiation given off. Therefore people given off. Therefore people give off infrared rays.give off infrared rays.
VISIBLE LIGHTVISIBLE LIGHT Shorter wavelength and higher frequency than infrared rays.Shorter wavelength and higher frequency than infrared rays. Electromagnetic waves we Electromagnetic waves we can see.can see. Longest wavelength= red lightLongest wavelength= red light Shortest wavelength= violet (purple) lightShortest wavelength= violet (purple) light When light enters a new medium it bends (refracts). Each When light enters a new medium it bends (refracts). Each
wavelength bends a different amount allowing white light to wavelength bends a different amount allowing white light to separate into it’s various colors separate into it’s various colors ROYGBIV.ROYGBIV.
ULTRAVIOLET RAYSULTRAVIOLET RAYS Shorter wavelength and higher frequency than Shorter wavelength and higher frequency than
visible lightvisible light Carry Carry more energymore energy than visible light than visible light Used to Used to kill bacteria.kill bacteria. (Sterilization of equipment) (Sterilization of equipment) Causes your skin to produce Causes your skin to produce vitamin Dvitamin D (good for (good for
teeth and bones)teeth and bones) Too much can cause skin cancer. Too much can cause skin cancer. Use sun block to protect against (UV rays)Use sun block to protect against (UV rays)
X- RAYSX- RAYS Shorter wavelength and higher frequency Shorter wavelength and higher frequency
than UV-raysthan UV-rays Carry a great amount of energyCarry a great amount of energy Can penetrate most matter.Can penetrate most matter. Bones and teethBones and teeth absorbabsorb x-rays. (The light x-rays. (The light
part of an x-ray image indicates a place part of an x-ray image indicates a place where the x-ray was absorbed)where the x-ray was absorbed)
Too much exposure Too much exposure can cause cancercan cause cancer (lead vest at dentist protects organs (lead vest at dentist protects organs
from unnecessary exposure)from unnecessary exposure)
Used by Used by engineersengineers to check for to check for tiny cracks in structures.tiny cracks in structures.
The rays pass through the cracks The rays pass through the cracks and the cracks appear dark on film.and the cracks appear dark on film.
GAMMA RAYSGAMMA RAYS Shorter wavelength and higher Shorter wavelength and higher
frequency than X-raysfrequency than X-rays Carry the Carry the greatest amount of energygreatest amount of energy
and penetrate the most.and penetrate the most. Used in Used in radiation treatmentradiation treatment to kill to kill
cancer cells.cancer cells. Can be very harmful if not used Can be very harmful if not used
correctly.correctly.
SUMMARYSUMMARY All electromagnetic wavesAll electromagnetic waves travel at the travel at the
same speed. (300,000,000 meters/second same speed. (300,000,000 meters/second in a vacuum.in a vacuum.
They all have different They all have different wavelengthwavelength and and different different frequencies.frequencies. Long wavelength-Long wavelength-lowest frequencylowest frequency Short wavelengthShort wavelength highest frequency highest frequency The higher the frequency the The higher the frequency the higher the higher the
energy.energy.
Light as ParticleLight as Particle
Light also behaves like a particleLight also behaves like a particle This particle is called This particle is called a photona photon The energy of a photon is dependent on The energy of a photon is dependent on
its frequencyits frequency A photon is like a little packet (quantum) of A photon is like a little packet (quantum) of
electromagnetic energy.electromagnetic energy.
Where do photons come from?Where do photons come from?
Photons come from atomsPhotons come from atoms Atoms absorb and emit photons at certain Atoms absorb and emit photons at certain
specific frequencies.specific frequencies. This is because the electrons can only be This is because the electrons can only be
in certain orbitals.in certain orbitals.
Atomic EmissionAtomic Emission
e-
This means…This means…
Atoms of an specific element absorb or Atoms of an specific element absorb or emit only specific frequencies of emit only specific frequencies of electromagnetic energy.electromagnetic energy.
This is called the absorption or emission This is called the absorption or emission spectrum. spectrum.
Using this in astronomyUsing this in astronomy
Astronomers can use these spectra to Astronomers can use these spectra to determine the composition of stars and determine the composition of stars and planets and other stellar objects.planets and other stellar objects.
The Sun’s Emission SpectrumThe Sun’s Emission Spectrum
Wave particle dualityWave particle duality
SUMMARYSUMMARY Light can also behave light particles Light can also behave light particles
called photons.called photons. These photons come from the electrons These photons come from the electrons
in atoms.in atoms. Because electrons can only be in Because electrons can only be in
specific orbitals, only specific specific orbitals, only specific frequencies are emitted or absorbed.frequencies are emitted or absorbed.
These specific frequencies (spectrum) These specific frequencies (spectrum) can be used to determine what elements can be used to determine what elements are present.are present.
Spectroscopy
Using wavelength/frequency to determine composition
Can use light emitted emission
Or light absorbed absorption
Light and temperature
Electromagnetic spectrum also tells temperature
More heat = more energy More energy = higher frequency Higher frequency = More heat
Thermal radiation
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
Kelvin is the astronomer’s temperature scale
Abbreviation : K K= ºC + 273 So… 0K = -273ºC
What’s colder than cold? Absolute zero! 0K Absolutely NO atomic motion
None Nada Zip Zilch No not even a little.
Deep space is just a few degrees above absolute zero
Summary
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 Light
Manipulating, or working with, light is what astronomers do
We have two main ways to manipulate light: Refraction Reflection
RefractionRefraction
Changing the direction of light as it passes Changing the direction of light as it passes through some mediumthrough some medium
For example:For example: Straw in drinkStraw in drink lenseslenses
RefractionRefraction
Refracting TelescopeRefracting Telescope
Focus light through a series of lensesFocus light through a series of lenses Like what Galileo usedLike what Galileo used
ReflectionReflection
Redirection of electromagnetic radiationRedirection of electromagnetic radiation Can be done with more than just visible Can be done with more than just visible
light!light!
Reflecting TelescopesReflecting Telescopes
Focus light through a series of mirrorsFocus light through a series of mirrors Invented by Isaac NewtonInvented by Isaac Newton
Reflecting TelescopesReflecting Telescopes
Allow for larger telescopesAllow for larger telescopes
English astronomer William Herschel built this huge reflecting telescope in the late 1700s.
Radio TelescopesRadio Telescopes Work like visible light reflector scopesWork like visible light reflector scopes Use the radio frequenciesUse the radio frequencies
Radio TelescopesRadio Telescopes
Radio AstronomyRadio Astronomy
Cassiopeia in visible lightCassiopeia in visible light Cassiopeia A in radioCassiopeia A in radio
Photoelectric EffectPhotoelectric Effect
Light hitting an object causes electrons to Light hitting an object causes electrons to be releasedbe released
Must be correct wavelength/frequencyMust be correct wavelength/frequency (amplitude not important)(amplitude not important)
Photoelectric effect in astronomyPhotoelectric effect in astronomy
Solar panels for spacecraftSolar panels for spacecraft Digital photographyDigital photography
Photography in AstronomyPhotography in Astronomy
As important a development as the As important a development as the telescopetelescope
Allows for sharing of informationAllows for sharing of information Allows for precise measurementsAllows for precise measurements