ELECTROMAGNETIC SPECTRUM

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.

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 phenomena

By using these different wavelengths, astronomers are able to gain a lot of information on various objects

Jupiter seen at different wavelengths of light tells you different things.

Light and EM Radiation Electromagnetic Radiation can travel

through empty space (without a medium). They travel as vibrations in electrical and

magnetic fields All forms of EM radiation travel at the

SAME SPEED. Speed of Light = 300,000 Km/sec

Speed of Sound = 340 m/sec (.340 km/sec)Click here Animation: Interaction of vibrating charges

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 material

A wave can carry both energy and information

Wave Terminology

Wavelength - distance between two like points on the wave

Amplitude - the height of the wave compared to undisturbed

state

Period - the amount of time required for one wavelength to

pass

Frequency - the number of waves passing in a given amount

of time

Electromagnetic SpectrumElectromagnetic Spectrum—name for the range of electromagnetic waves when placed in order of increasing frequency• Click here (Animation—Size of EMwaves)

The Electromagnetic Spectrum

Human eyes see the visible part of the spectrum

Longer wavelengths includes infrared light, microwaves, and radio

Shorter wavelengths includes ultraviolet light, X-rays, and gamma rays

All of these are forms of electromagnetic radiation

RADIO WAVES

A. 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.

MRI of the Brain MRI (MAGNETIC RESONACE IMAGING)

Uses Short wave radio waves with a magnet to create an image

Radio Waves

FM=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.

MICROWAVES

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 (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.

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 skin

Heat lamps give off infrared waves. Warm objects give off more heat energy than

cool objects.

INFRARED RAYSThermogram—a picture that shows regions of different temperatures in the body.

Wavelengths of Light - Visible

What we see as white light is actually made up of a continuum of components

We break white light into red, orange, yellow, green, blue, indigo, and violet (ROY G BIV) Red is the LONGEST Violet is the

SHORTEST

Visible light is the Smallest section of the EM Spectrum

ULTRAVIOLET RADIATION• Referred to as UV rays• 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)• Used to treat jaundice ( in some new born babies.• Too much can cause skin cancer. • Use sun block to protect against (UV rays)

XRAY RADIATION• 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)

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.

EM Spectrum in Astronomy

If we could only observe in visible light, our knowledge of the universe would be greatly limited

By looking at objects at different wavelengths, we get a different view and lots more information

Some objects are only visible at certain wavelengths

The Sun at Different Wavelengths

Visible Ultraviolet

X-ray X-ray

TELESCOPES

Invented by Dutch lens maker in 1608 Galileo: designed small 30X scope Observed the moon and “began” the modern

age of Astronomy where measurement was more important than philosophy

General types of Telescopes

Refracting (objective is a glass lens) Reflecting (objective is a mirror)

Newtonian Cassegrain

Problems with Earth-based telescopes

Earth’s atmosphere reflects certain wavelengths x-rays, gamma rays and most UV light is

not transmitted by our atmosphere Earth’s atmosphere blurs images

the 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.

Advantages of Space Telescopes

Can collect EM wavelengths that do not penetrate the Earth’s atmosphere Gamma rays X-rays Most Ultraviolet waves

Can collect all EM radiation without disruption from Earth’s atmosphere Images MUCH sharper

Disadvantages of space-based telescopes

Expensive to launch and maintain

Difficult to repair Short lifetime

HUBBLE SPACE TELESCOPE

Launched in 1990 Mirror error fixed

‘93 15 yr life

expectancy Going on year 20!!

96 minutes for 1 orbit around Earth

HUBBLE IMAGES