Electromagnetic Spectrum

Use in Astronomy

What is the Electromagnetic Spectrum?-- Made of all of the electromagnetic waves.

-- What is an electromagnetic wave?-- Just what it says: vibrations

of electric and magnetic fields.

This is hard to visualize: Lets compare this to something more tangible: Sound waves can beheard. On a piano thelow notes have a longwavelength and low frequency.

With a sound wave: Air vibrates, or water.That is the reason sound requires a

medium to travel through.

What vibrates with an Electromagnetic Wave?

The electric and magnetic fields vibrate.

But E fields and B fields require nothing to travel through. So light travelsthrough empty space.

What do you need to know about the Spectrum?

The names of the types of wave.The order that they're arranged in.The uses of each type of wave.How each type of wave is made.The dangers of each type of wave.All electromagnetic waves can cross a vacuum.All electromagnetic waves travel at

the speed of light.

http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html

Radio Waves: Radio waves are made by various types of transmitter, depending on the wavelength. They are also given off by stars, sparks and lightning, which is why you hear interference on your radio in a thunderstorm.

Uses: Your radio captures radio waves emitted by radio stations, bringing your favorite tunes. Radio waves are also emitted by stars and gases in space.

Microwaves: Microwaves are basically extremely high frequency radio waves, and are made by various types of transmitters.In a mobile phone, they're made by a transmitter chip and an antenna, in a microwave oven they're made by a "magnetron". Stars also give off microwaves.

Uses: Microwave radiation will cook your popcorn in just a few minutes, but is also used by astronomers to learn about the

structure of nearby galaxies.

Infrared Waves: Infra red waves are just below

visible red light in the electromagnetic spectrum ("Infra" means "below"). You probably think of Infra-red waves as heat, because they're given off by hot objects, and you can feel them as warmth on your skin.Infra Red waves are also given off by stars, lamps, flamesand anything else that's warm - including you.

Uses: Night vision goggles pick up the infrared light emitted

by our skin and objects with heat. In space,infrared light helps us map the

dust between stars.

Visible Light: Our eyes can detect only a tiny part of the

electromagnetic spectrum, called visible light.This means that there's a great deal happening around us that we're simply not aware of, unless we have instruments to detect it.Light waves are given off by anything that's hot enough to glow. This is how light bulbs work - an electric current heats the lamp filament to around 3,000 degrees, and it glows white-hot. The surface of the Sun is around 5,600 degrees, and it gives off a great deal of light.

White light is actually made up of a whole range of colors,

mixed together.

We can see this if we pass white light through a glass prism -

the violet light is bent ("refracted") more than the red, because

it has a shorter wavelength - and we see a rainbow of colors.

This is called 'dispersion', and allows us to work out what stars

are made of by looking at the mixture of wavelengths in the

light.

Uses: We use light to see

things! As the Sun

sends so much light

towards our planet,

we've evolved to make

use of those particular

wavelengths in order to

sense our environment.

Light waves can also be made using a laser. This works

differently to a light bulb, and produces "coherent" light.

Lasers are used in Compact Disc & DVD players,

where the light is reflected from the tiny pits in the disc,

and the pattern is detected and translated into sound or

data.

Lasers are also used in laser printers, and in

aircraft weapon aiming systems.

To find out more about laser printers, see

http://computer.howstuffworks.com/laser-

printer1.htm

The photo shows a UV lamp in a chip shop.

The lamp gives off UV (which you can't see) as well as violet light (which you can see).

The UV attracts insects, which are

electrocuted by high-voltage wires near the

lamp - so they won't land on the food and contaminate it.

Ultraviolet light: Made by special

lamps, for example, on sun beds. It is

given off by the Sun in large quantities.

We call it "UV" for short.

Uses: Uses for UV light include getting a sun tan, detecting forged bank notes in shops, and hardening some types of dental filling. You also see UV lamps in clubs, where they make your clothes glow. This happens because substances in washing powder "fluoresce" when UV light strikes them - they absorb the UV and then re-radiate the energy at a longer wavelength. The lamps are sometimes called "blacklights" because we can't see the UV coming from them.

Uses Ultraviolet Light: When you mark your possessions with a security marker pen, the ink is invisible unless you shine a UV lamp at it.Ultraviolet rays can be used to kill microbes. Hospitals use UV lamps to sterilize surgical equipment and the air in operating theatres. Food and drug companies also use UV lamps to sterilize their products.Suitable doses of Ultraviolet rays cause the body to produce vitamin D, and this is used by doctors to treat vitamin D deficiency and some skin disorders.

"Hot" objects in space emit UV radiation as well.

X-Rays: X-rays are very high frequency waves, and carry a lot of energy. They will pass through most substances, and this makes them useful in medicine and industry to see inside things.X-rays are given off by stars, and strongly by some types of nebula. An X-ray machine works by firing a beam of electrons at a "target". If we fire the electrons with enough energy, X-rays will be produced.

Uses of X-Rays:

X-rays are used by doctors to see inside people.

The machines are managed by a trained x-ray

technician. They pass easily through soft tissues,

but not so easily through bones. We send a beam

of X-Rays through the patient and onto a piece of

film, which goes dark where X-Rays hit it. This

leaves white patches on the film where the bones were in the way.

Sometimes a doctor will give a patient a "Barium

Meal", which is a drink of Barium Sulphate. This

will absorb X-rays, and so the patient's intestines will show up clearly on a X-Ray image.

X-Rays are also used in airport security checks, to see inside your luggage.

They are also used by astronomers - many objects in the universe emit X-rays, which we can detect using suitable radio telescopes.

Lower energy X-Rays don't pass through tissues as easily, and can be used to scan soft areas such as the brain

Gamma Rays: Gamma rays are given off by

stars, and by some radioactive substances. They are extremely high frequency waves, and carry a large amount of energy.

They pass through most materials, and are quite

difficult to stop - you need lead or concrete in order to block them out.

Uses of Gamma Rays: Because Gamma rays can kill living cells, they are used to kill cancer cellswithout having to resort to difficult surgery. This is called "Radiotherapy", and works because cancer cells can't repair themselves like healthy cells can when damaged by gamma rays. Getting the dose right is very important! There's also targeted radiotherapy, where a radioactive substance is used to kill cancer cells - but it's a substance that'll be taken up by a specific part of the body, so the rest of the body only gets a low dose. An example would be using radioactive iodine to treat cancer in the thyroid gland.

Uses of Gamma Rays:

Example:the picture on the right is a "Scintigram", and

shows an asthmatic person's lungs.

The patient was given a slightly radioactive gas to

breathe, and the picture was taken using a gamma

camera to detect the radiation. The colors show the air

flow in the lungs.

In industry, radioactive "tracer" substances can be put

into pipes and machinery, then we can detect where the

substances go. This is basically the same use as in

medicine

Gamma rays kill microbes, and are

used to sterilize food so that it will

keep fresh for longer.

This is known as "irradiated" food.

Tracers:

Doctors can put slightly radioactive substances into a patient's

body, then scan the patient to detect the gamma rays and build

up a picture of what's going on inside the patient. This is very

useful because they can see the body processes actually working,

rather than just looking at still pictures.

Is a Radio Wave a the same as a gammaray?

They are produced in different processes and are detected in different ways, but they are not fundamentally different. Radio waves, gamma-rays, visible light, and all the other parts of the electromagnetic spectrum are electromagnetic radiation. Electromagnetic radiation can be described in terms of a stream of mass-less particles, called photons, each traveling in a wave-like pattern at the speed of light. Each photon contains a certain amount of energy. The different types of radiation are defined by the amount of energy found in the photons.

Radio waves have photons with low energies, microwave photons have a little more energy than radio waves, infrared photons have still more, then visible, ultraviolet, X-rays, and, the most energetic of all, gamma-rays.

Crab Nebula in visible light

Uses in Astronomy:

Fermi Bubbles:

Fermi Gamma Ray Telescope.

ch 3--info for spectraluseppt.docx

Visible Infrared Overlay

http://sci.esa.int/education/34990-wavelength