2 Electromagnetic Radiation Definition: Radiant energy emitted by all matter whose temperature is greater than absolute zero (0° K).Best known as VISIBLE LIGHT but includes radio waves and ultraviolet waves too.
3 Light and the EM Spectrum The terms light, radiation, and electromagnetic wave can all be used to explain the same concept.Light comes in many forms.x-rays, visible light, radio waves, etc. are all the same phenomenaBy using these different wavelengths, astronomers are able to gain a lot of information on various objectsJupiter seen at different wavelengths of light tells you different things.
4 Light and EM RadiationElectromagnetic Radiation can travel through empty space (without a medium).They travel as vibrations in electrical and magnetic fieldsAll forms of EM radiation travel at the SAME SPEED.Speed of Light = 300,000 Km/secSpeed of Sound = 340 m/sec (.340 km/sec)Click here Animation: Interaction of vibrating charges
5 Light as Waves One way to think about light is as a traveling wave A wave is just a disturbance in some medium (water, air, space)A wave travels through a medium but does not transport materialA wave can carry both energy and information
6 Wave TerminologyWavelength - distance between two like points on the waveAmplitude - the height of the wave compared to undisturbed statePeriod - the amount of time required for one wavelength to passFrequency - the number of waves passing in a given amount of time
7 Electromagnetic Spectrum Electromagnetic Spectrum—name for the range of electromagnetic waves when placed in order of increasing frequencyClick here (Animation—Size of EMwaves)
8 The Electromagnetic Spectrum Human eyes see the visible part of the spectrumLonger wavelengths includes infrared light, microwaves, and radioShorter wavelengths includes ultraviolet light, X-rays, and gamma raysAll of these are forms of electromagnetic radiation
9 RADIO WAVESA. Have the longest wavelengths and lowest frequencies of all the electromagnetic waves.B. A radio picks up radio waves through an antenna and converts it to sound waves.C. Each radio station in an area broadcasts at a different frequency. # on radio dial tells frequency.
10 MRI of the Brain MRI (MAGNETIC RESONACE IMAGING) Uses Short wave radio waves with a magnet to create an image
11 Radio WavesFM=Frequency modulation—waves travel in a straight line & through the ionosphere--lose reception when you travel out of range.AM=Amplitude modulation—waves bounce off ionosphere can pick up stations from different cities.
12 MICROWAVESMicrowaves—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 (Radio Detection and Ranging)Used to find the speed of an object by sending out radio waves and measuring the time it takes them to return.
13 INFRARED RAYS Infrared= LONGER than the color red Shorter wavelength and higher frequency than microwaves.You can feel the longest ones as warmth on your skinHeat lamps give off infrared waves.Warm objects give off more heat energy than cool objects.
14 INFRARED RAYSThermogram—a picture that shows regions of different temperatures in the body.
15 Wavelengths of Light - Visible What we see as white light is actually made up of a continuum of componentsWe break white light into red, orange, yellow, green, blue, indigo, and violet (ROY G BIV)Red is the LONGESTViolet is the SHORTESTVisible light is the Smallest section of the EM Spectrum
16 ULTRAVIOLET RADIATION Referred to as UV raysShorter wavelength and higher frequency than visible lightCarry more energy than visible lightUsed to kill bacteria. (Sterilization of equipment)Causes your skin to produce vitamin D (good for teeth and bones)Used to treat jaundice ( in some new born babies.Too much can cause skin cancer.Use sun block to protect against (UV rays)
17 XRAY RADIATION Shorter wavelength and higher frequency than UV-rays Carry a great amount of energyCan 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)
18 GAMMA RADIATION 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.
19 EM Spectrum in Astronomy If we could only observe in visible light, our knowledge of the universe would be greatly limitedBy looking at objects at different wavelengths, we get a different view and lots more informationSome objects are only visible at certain wavelengths
21 The Sun at Different Wavelengths VisibleUltravioletX-rayX-ray
22 TELESCOPES Invented by Dutch lens maker in 1608 Galileo: designed small 30X scopeObserved the moon and “began” the modern age of Astronomy where measurement was more important than philosophy
23 General types of Telescopes Refracting (objective is a glass lens)Reflecting (objective is a mirror)NewtonianCassegrain
24 Problems with Earth-based telescopes Earth’s atmosphere reflects certain wavelengthsx-rays, gamma rays and most UV light is not transmitted by our atmosphereEarth’s atmosphere blurs imagesthe bending of light by the atmosphere depends on the temperature of the “air”“twinkling of stars” (Caused by movement of air)“Light pollution”Solution? Put the telescope in space.
25 Advantages of Space Telescopes Can collect EM wavelengths that do not penetrate the Earth’s atmosphereGamma raysX-raysMost Ultraviolet wavesCan collect all EM radiation without disruption from Earth’s atmosphereImages MUCH sharper
26 Disadvantages of space-based telescopes Expensive to launch and maintainDifficult to repairShort lifetime
27 HUBBLE SPACE TELESCOPE Launched in 1990Mirror error fixed ‘9315 yr life expectancyGoing on year 20!!96 minutes for 1 orbit around Earth